/usr/src/gnu/usr.bin/clang/libclangSema/../../../llvm/clang/lib/Sema/SemaTemplateDeduction.cpp

Bug Summary

File:	src/gnu/usr.bin/clang/libclangSema/../../../llvm/clang/lib/Sema/SemaTemplateDeduction.cpp
Warning:	line 3307, column 7 Called C++ object pointer is null
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1//===- SemaTemplateDeduction.cpp - Template Argument Deduction ------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements C++ template argument deduction.
10//
11//===----------------------------------------------------------------------===//

13#include "clang/Sema/TemplateDeduction.h"
14#include "TreeTransform.h"
15#include "TypeLocBuilder.h"
16#include "clang/AST/ASTContext.h"
17#include "clang/AST/ASTLambda.h"
18#include "clang/AST/Decl.h"
19#include "clang/AST/DeclAccessPair.h"
20#include "clang/AST/DeclBase.h"
21#include "clang/AST/DeclCXX.h"
22#include "clang/AST/DeclTemplate.h"
23#include "clang/AST/DeclarationName.h"
24#include "clang/AST/Expr.h"
25#include "clang/AST/ExprCXX.h"
26#include "clang/AST/NestedNameSpecifier.h"
27#include "clang/AST/RecursiveASTVisitor.h"
28#include "clang/AST/TemplateBase.h"
29#include "clang/AST/TemplateName.h"
30#include "clang/AST/Type.h"
31#include "clang/AST/TypeLoc.h"
32#include "clang/AST/UnresolvedSet.h"
33#include "clang/Basic/AddressSpaces.h"
34#include "clang/Basic/ExceptionSpecificationType.h"
35#include "clang/Basic/LLVM.h"
36#include "clang/Basic/LangOptions.h"
37#include "clang/Basic/PartialDiagnostic.h"
38#include "clang/Basic/SourceLocation.h"
39#include "clang/Basic/Specifiers.h"
40#include "clang/Sema/Ownership.h"
41#include "clang/Sema/Sema.h"
42#include "clang/Sema/Template.h"
43#include "llvm/ADT/APInt.h"
44#include "llvm/ADT/APSInt.h"
45#include "llvm/ADT/ArrayRef.h"
46#include "llvm/ADT/DenseMap.h"
47#include "llvm/ADT/FoldingSet.h"
48#include "llvm/ADT/Optional.h"
49#include "llvm/ADT/SmallBitVector.h"
50#include "llvm/ADT/SmallPtrSet.h"
51#include "llvm/ADT/SmallVector.h"
52#include "llvm/Support/Casting.h"
53#include "llvm/Support/Compiler.h"
54#include "llvm/Support/ErrorHandling.h"
55#include <algorithm>
56#include <cassert>
57#include <tuple>
58#include <utility>

60namespace clang {

/// Various flags that control template argument deduction.
///
/// These flags can be bitwise-OR'd together.
enum TemplateDeductionFlags {
  /// No template argument deduction flags, which indicates the
  /// strictest results for template argument deduction (as used for, e.g.,
  /// matching class template partial specializations).
  TDF_None = 0,

  /// Within template argument deduction from a function call, we are
  /// matching with a parameter type for which the original parameter was
  /// a reference.
  TDF_ParamWithReferenceType = 0x1,

  /// Within template argument deduction from a function call, we
  /// are matching in a case where we ignore cv-qualifiers.
  TDF_IgnoreQualifiers = 0x02,

  /// Within template argument deduction from a function call,
  /// we are matching in a case where we can perform template argument
  /// deduction from a template-id of a derived class of the argument type.
  TDF_DerivedClass = 0x04,

  /// Allow non-dependent types to differ, e.g., when performing
  /// template argument deduction from a function call where conversions
  /// may apply.
  TDF_SkipNonDependent = 0x08,

  /// Whether we are performing template argument deduction for
  /// parameters and arguments in a top-level template argument
  TDF_TopLevelParameterTypeList = 0x10,

  /// Within template argument deduction from overload resolution per
  /// C++ [over.over] allow matching function types that are compatible in
  /// terms of noreturn and default calling convention adjustments, or
  /// similarly matching a declared template specialization against a
  /// possible template, per C++ [temp.deduct.decl]. In either case, permit
  /// deduction where the parameter is a function type that can be converted
  /// to the argument type.
  TDF_AllowCompatibleFunctionType = 0x20,

  /// Within template argument deduction for a conversion function, we are
  /// matching with an argument type for which the original argument was
  /// a reference.
  TDF_ArgWithReferenceType = 0x40,
};
108}

110using namespace clang;
111using namespace sema;

113/// Compare two APSInts, extending and switching the sign as
114/// necessary to compare their values regardless of underlying type.
115static bool hasSameExtendedValue(llvm::APSInt X, llvm::APSInt Y) {
if (Y.getBitWidth() > X.getBitWidth())
  X = X.extend(Y.getBitWidth());
else if (Y.getBitWidth() < X.getBitWidth())
  Y = Y.extend(X.getBitWidth());

// If there is a signedness mismatch, correct it.
if (X.isSigned() != Y.isSigned()) {
  // If the signed value is negative, then the values cannot be the same.
  if ((Y.isSigned() && Y.isNegative()) || (X.isSigned() && X.isNegative()))
    return false;

  Y.setIsSigned(true);
  X.setIsSigned(true);
}

return X == Y;
132}

134static Sema::TemplateDeductionResult
135DeduceTemplateArguments(Sema &S,
                      TemplateParameterList *TemplateParams,
                      const TemplateArgument &Param,
                      TemplateArgument Arg,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced);

142static Sema::TemplateDeductionResult
143DeduceTemplateArgumentsByTypeMatch(Sema &S,
                                 TemplateParameterList *TemplateParams,
                                 QualType Param,
                                 QualType Arg,
                                 TemplateDeductionInfo &Info,
                                 SmallVectorImpl<DeducedTemplateArgument> &
                                                    Deduced,
                                 unsigned TDF,
                                 bool PartialOrdering = false,
                                 bool DeducedFromArrayBound = false);

154static Sema::TemplateDeductionResult
155DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
                      ArrayRef<TemplateArgument> Params,
                      ArrayRef<TemplateArgument> Args,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                      bool NumberOfArgumentsMustMatch);

162static void MarkUsedTemplateParameters(ASTContext &Ctx,
                                     const TemplateArgument &TemplateArg,
                                     bool OnlyDeduced, unsigned Depth,
                                     llvm::SmallBitVector &Used);

167static void MarkUsedTemplateParameters(ASTContext &Ctx, QualType T,
                                     bool OnlyDeduced, unsigned Level,
                                     llvm::SmallBitVector &Deduced);

171/// If the given expression is of a form that permits the deduction
172/// of a non-type template parameter, return the declaration of that
173/// non-type template parameter.
174static const NonTypeTemplateParmDecl *
175getDeducedParameterFromExpr(const Expr *E, unsigned Depth) {
// If we are within an alias template, the expression may have undergone
// any number of parameter substitutions already.
while (true) {
  if (const auto *IC = dyn_cast<ImplicitCastExpr>(E))
    E = IC->getSubExpr();
  else if (const auto *CE = dyn_cast<ConstantExpr>(E))
    E = CE->getSubExpr();
  else if (const auto *Subst = dyn_cast<SubstNonTypeTemplateParmExpr>(E))
    E = Subst->getReplacement();
  else if (const auto *CCE = dyn_cast<CXXConstructExpr>(E)) {
    // Look through implicit copy construction from an lvalue of the same type.
    if (CCE->getParenOrBraceRange().isValid())
      break;
    // Note, there could be default arguments.
    assert(CCE->getNumArgs() >= 1 && "implicit construct expr should have 1 arg")((void)0);
    E = CCE->getArg(0);
  } else
    break;
}

if (const auto *DRE = dyn_cast<DeclRefExpr>(E))
  if (const auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(DRE->getDecl()))
    if (NTTP->getDepth() == Depth)
      return NTTP;

return nullptr;
202}

204static const NonTypeTemplateParmDecl *
205getDeducedParameterFromExpr(TemplateDeductionInfo &Info, Expr *E) {
return getDeducedParameterFromExpr(E, Info.getDeducedDepth());
207}

209/// Determine whether two declaration pointers refer to the same
210/// declaration.
211static bool isSameDeclaration(Decl *X, Decl *Y) {
if (NamedDecl *NX = dyn_cast<NamedDecl>(X))
  X = NX->getUnderlyingDecl();
if (NamedDecl *NY = dyn_cast<NamedDecl>(Y))
  Y = NY->getUnderlyingDecl();

return X->getCanonicalDecl() == Y->getCanonicalDecl();
218}

220/// Verify that the given, deduced template arguments are compatible.
221///
222/// \returns The deduced template argument, or a NULL template argument if
223/// the deduced template arguments were incompatible.
224static DeducedTemplateArgument
225checkDeducedTemplateArguments(ASTContext &Context,
                            const DeducedTemplateArgument &X,
                            const DeducedTemplateArgument &Y) {
// We have no deduction for one or both of the arguments; they're compatible.
if (X.isNull())
  return Y;
if (Y.isNull())
  return X;

// If we have two non-type template argument values deduced for the same
// parameter, they must both match the type of the parameter, and thus must
// match each other's type. As we're only keeping one of them, we must check
// for that now. The exception is that if either was deduced from an array
// bound, the type is permitted to differ.
if (!X.wasDeducedFromArrayBound() && !Y.wasDeducedFromArrayBound()) {
  QualType XType = X.getNonTypeTemplateArgumentType();
  if (!XType.isNull()) {
    QualType YType = Y.getNonTypeTemplateArgumentType();
    if (YType.isNull() || !Context.hasSameType(XType, YType))
      return DeducedTemplateArgument();
  }
}

switch (X.getKind()) {
case TemplateArgument::Null:
  llvm_unreachable("Non-deduced template arguments handled above")__builtin_unreachable();

case TemplateArgument::Type:
  // If two template type arguments have the same type, they're compatible.
  if (Y.getKind() == TemplateArgument::Type &&
      Context.hasSameType(X.getAsType(), Y.getAsType()))
    return X;

  // If one of the two arguments was deduced from an array bound, the other
  // supersedes it.
  if (X.wasDeducedFromArrayBound() != Y.wasDeducedFromArrayBound())
    return X.wasDeducedFromArrayBound() ? Y : X;

  // The arguments are not compatible.
  return DeducedTemplateArgument();

case TemplateArgument::Integral:
  // If we deduced a constant in one case and either a dependent expression or
  // declaration in another case, keep the integral constant.
  // If both are integral constants with the same value, keep that value.
  if (Y.getKind() == TemplateArgument::Expression ||
      Y.getKind() == TemplateArgument::Declaration ||
      (Y.getKind() == TemplateArgument::Integral &&
       hasSameExtendedValue(X.getAsIntegral(), Y.getAsIntegral())))
    return X.wasDeducedFromArrayBound() ? Y : X;

  // All other combinations are incompatible.
  return DeducedTemplateArgument();

case TemplateArgument::Template:
  if (Y.getKind() == TemplateArgument::Template &&
      Context.hasSameTemplateName(X.getAsTemplate(), Y.getAsTemplate()))
    return X;

  // All other combinations are incompatible.
  return DeducedTemplateArgument();

case TemplateArgument::TemplateExpansion:
  if (Y.getKind() == TemplateArgument::TemplateExpansion &&
      Context.hasSameTemplateName(X.getAsTemplateOrTemplatePattern(),
                                  Y.getAsTemplateOrTemplatePattern()))
    return X;

  // All other combinations are incompatible.
  return DeducedTemplateArgument();

case TemplateArgument::Expression: {
  if (Y.getKind() != TemplateArgument::Expression)
    return checkDeducedTemplateArguments(Context, Y, X);

  // Compare the expressions for equality
  llvm::FoldingSetNodeID ID1, ID2;
  X.getAsExpr()->Profile(ID1, Context, true);
  Y.getAsExpr()->Profile(ID2, Context, true);
  if (ID1 == ID2)
    return X.wasDeducedFromArrayBound() ? Y : X;

  // Differing dependent expressions are incompatible.
  return DeducedTemplateArgument();
}

case TemplateArgument::Declaration:
  assert(!X.wasDeducedFromArrayBound())((void)0);

  // If we deduced a declaration and a dependent expression, keep the
  // declaration.
  if (Y.getKind() == TemplateArgument::Expression)
    return X;

  // If we deduced a declaration and an integral constant, keep the
  // integral constant and whichever type did not come from an array
  // bound.
  if (Y.getKind() == TemplateArgument::Integral) {
    if (Y.wasDeducedFromArrayBound())
      return TemplateArgument(Context, Y.getAsIntegral(),
                              X.getParamTypeForDecl());
    return Y;
  }

  // If we deduced two declarations, make sure that they refer to the
  // same declaration.
  if (Y.getKind() == TemplateArgument::Declaration &&
      isSameDeclaration(X.getAsDecl(), Y.getAsDecl()))
    return X;

  // All other combinations are incompatible.
  return DeducedTemplateArgument();

case TemplateArgument::NullPtr:
  // If we deduced a null pointer and a dependent expression, keep the
  // null pointer.
  if (Y.getKind() == TemplateArgument::Expression)
    return X;

  // If we deduced a null pointer and an integral constant, keep the
  // integral constant.
  if (Y.getKind() == TemplateArgument::Integral)
    return Y;

  // If we deduced two null pointers, they are the same.
  if (Y.getKind() == TemplateArgument::NullPtr)
    return X;

  // All other combinations are incompatible.
  return DeducedTemplateArgument();

case TemplateArgument::Pack: {
  if (Y.getKind() != TemplateArgument::Pack ||
      X.pack_size() != Y.pack_size())
    return DeducedTemplateArgument();

  llvm::SmallVector<TemplateArgument, 8> NewPack;
  for (TemplateArgument::pack_iterator XA = X.pack_begin(),
                                    XAEnd = X.pack_end(),
                                       YA = Y.pack_begin();
       XA != XAEnd; ++XA, ++YA) {
    TemplateArgument Merged = checkDeducedTemplateArguments(
        Context, DeducedTemplateArgument(*XA, X.wasDeducedFromArrayBound()),
        DeducedTemplateArgument(*YA, Y.wasDeducedFromArrayBound()));
    if (Merged.isNull() && !(XA->isNull() && YA->isNull()))
      return DeducedTemplateArgument();
    NewPack.push_back(Merged);
  }

  return DeducedTemplateArgument(
      TemplateArgument::CreatePackCopy(Context, NewPack),
      X.wasDeducedFromArrayBound() && Y.wasDeducedFromArrayBound());
}
}

llvm_unreachable("Invalid TemplateArgument Kind!")__builtin_unreachable();
381}

383/// Deduce the value of the given non-type template parameter
384/// as the given deduced template argument. All non-type template parameter
385/// deduction is funneled through here.
386static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
  Sema &S, TemplateParameterList *TemplateParams,
  const NonTypeTemplateParmDecl *NTTP, const DeducedTemplateArgument &NewDeduced,
  QualType ValueType, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
assert(NTTP->getDepth() == Info.getDeducedDepth() &&((void)0)
       "deducing non-type template argument with wrong depth")((void)0);

DeducedTemplateArgument Result = checkDeducedTemplateArguments(
    S.Context, Deduced[NTTP->getIndex()], NewDeduced);
if (Result.isNull()) {
  Info.Param = const_cast<NonTypeTemplateParmDecl*>(NTTP);
  Info.FirstArg = Deduced[NTTP->getIndex()];
  Info.SecondArg = NewDeduced;
  return Sema::TDK_Inconsistent;
}

Deduced[NTTP->getIndex()] = Result;
if (!S.getLangOpts().CPlusPlus17)
  return Sema::TDK_Success;

if (NTTP->isExpandedParameterPack())
  // FIXME: We may still need to deduce parts of the type here! But we
  // don't have any way to find which slice of the type to use, and the
  // type stored on the NTTP itself is nonsense. Perhaps the type of an
  // expanded NTTP should be a pack expansion type?
  return Sema::TDK_Success;

// Get the type of the parameter for deduction. If it's a (dependent) array
// or function type, we will not have decayed it yet, so do that now.
QualType ParamType = S.Context.getAdjustedParameterType(NTTP->getType());
if (auto *Expansion = dyn_cast<PackExpansionType>(ParamType))
  ParamType = Expansion->getPattern();

// FIXME: It's not clear how deduction of a parameter of reference
// type from an argument (of non-reference type) should be performed.
// For now, we just remove reference types from both sides and let
// the final check for matching types sort out the mess.
ValueType = ValueType.getNonReferenceType();
if (ParamType->isReferenceType())
  ParamType = ParamType.getNonReferenceType();
else
  // Top-level cv-qualifiers are irrelevant for a non-reference type.
  ValueType = ValueType.getUnqualifiedType();

return DeduceTemplateArgumentsByTypeMatch(
    S, TemplateParams, ParamType, ValueType, Info, Deduced,
    TDF_SkipNonDependent, /*PartialOrdering=*/false,
    /*ArrayBound=*/NewDeduced.wasDeducedFromArrayBound());
435}

437/// Deduce the value of the given non-type template parameter
438/// from the given integral constant.
439static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
  Sema &S, TemplateParameterList *TemplateParams,
  const NonTypeTemplateParmDecl *NTTP, const llvm::APSInt &Value,
  QualType ValueType, bool DeducedFromArrayBound, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
return DeduceNonTypeTemplateArgument(
    S, TemplateParams, NTTP,
    DeducedTemplateArgument(S.Context, Value, ValueType,
                            DeducedFromArrayBound),
    ValueType, Info, Deduced);
449}

451/// Deduce the value of the given non-type template parameter
452/// from the given null pointer template argument type.
453static Sema::TemplateDeductionResult DeduceNullPtrTemplateArgument(
  Sema &S, TemplateParameterList *TemplateParams,
  const NonTypeTemplateParmDecl *NTTP, QualType NullPtrType,
  TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
Expr *Value = S.ImpCastExprToType(
                   new (S.Context) CXXNullPtrLiteralExpr(S.Context.NullPtrTy,
                                                         NTTP->getLocation()),
                   NullPtrType,
                   NullPtrType->isMemberPointerType() ? CK_NullToMemberPointer
                                                      : CK_NullToPointer)
                  .get();
return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                     DeducedTemplateArgument(Value),
                                     Value->getType(), Info, Deduced);
468}

470/// Deduce the value of the given non-type template parameter
471/// from the given type- or value-dependent expression.
472///
473/// \returns true if deduction succeeded, false otherwise.
474static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
  Sema &S, TemplateParameterList *TemplateParams,
  const NonTypeTemplateParmDecl *NTTP, Expr *Value, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                     DeducedTemplateArgument(Value),
                                     Value->getType(), Info, Deduced);
481}

483/// Deduce the value of the given non-type template parameter
484/// from the given declaration.
485///
486/// \returns true if deduction succeeded, false otherwise.
487static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
  Sema &S, TemplateParameterList *TemplateParams,
  const NonTypeTemplateParmDecl *NTTP, ValueDecl *D, QualType T,
  TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
D = D ? cast<ValueDecl>(D->getCanonicalDecl()) : nullptr;
TemplateArgument New(D, T);
return DeduceNonTypeTemplateArgument(
    S, TemplateParams, NTTP, DeducedTemplateArgument(New), T, Info, Deduced);
496}

498static Sema::TemplateDeductionResult
499DeduceTemplateArguments(Sema &S,
                      TemplateParameterList *TemplateParams,
                      TemplateName Param,
                      TemplateName Arg,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
TemplateDecl *ParamDecl = Param.getAsTemplateDecl();
if (!ParamDecl) {
  // The parameter type is dependent and is not a template template parameter,
  // so there is nothing that we can deduce.
  return Sema::TDK_Success;
}

if (TemplateTemplateParmDecl *TempParam
      = dyn_cast<TemplateTemplateParmDecl>(ParamDecl)) {
  // If we're not deducing at this depth, there's nothing to deduce.
  if (TempParam->getDepth() != Info.getDeducedDepth())
    return Sema::TDK_Success;

  DeducedTemplateArgument NewDeduced(S.Context.getCanonicalTemplateName(Arg));
  DeducedTemplateArgument Result = checkDeducedTemplateArguments(S.Context,
                                               Deduced[TempParam->getIndex()],
                                                                 NewDeduced);
  if (Result.isNull()) {
    Info.Param = TempParam;
    Info.FirstArg = Deduced[TempParam->getIndex()];
    Info.SecondArg = NewDeduced;
    return Sema::TDK_Inconsistent;
  }

  Deduced[TempParam->getIndex()] = Result;
  return Sema::TDK_Success;
}

// Verify that the two template names are equivalent.
if (S.Context.hasSameTemplateName(Param, Arg))
  return Sema::TDK_Success;

// Mismatch of non-dependent template parameter to argument.
Info.FirstArg = TemplateArgument(Param);
Info.SecondArg = TemplateArgument(Arg);
return Sema::TDK_NonDeducedMismatch;
541}

543/// Deduce the template arguments by comparing the template parameter
544/// type (which is a template-id) with the template argument type.
545///
546/// \param S the Sema
547///
548/// \param TemplateParams the template parameters that we are deducing
549///
550/// \param Param the parameter type
551///
552/// \param Arg the argument type
553///
554/// \param Info information about the template argument deduction itself
555///
556/// \param Deduced the deduced template arguments
557///
558/// \returns the result of template argument deduction so far. Note that a
559/// "success" result means that template argument deduction has not yet failed,
560/// but it may still fail, later, for other reasons.
561static Sema::TemplateDeductionResult
562DeduceTemplateArguments(Sema &S,
                      TemplateParameterList *TemplateParams,
                      const TemplateSpecializationType *Param,
                      QualType Arg,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
assert(Arg.isCanonical() && "Argument type must be canonical")((void)0);

// Treat an injected-class-name as its underlying template-id.
if (auto *Injected = dyn_cast<InjectedClassNameType>(Arg))
  Arg = Injected->getInjectedSpecializationType();

// Check whether the template argument is a dependent template-id.
if (const TemplateSpecializationType *SpecArg
      = dyn_cast<TemplateSpecializationType>(Arg)) {
  // Perform template argument deduction for the template name.
  if (Sema::TemplateDeductionResult Result
        = DeduceTemplateArguments(S, TemplateParams,
                                  Param->getTemplateName(),
                                  SpecArg->getTemplateName(),
                                  Info, Deduced))
    return Result;


  // Perform template argument deduction on each template
  // argument. Ignore any missing/extra arguments, since they could be
  // filled in by default arguments.
  return DeduceTemplateArguments(S, TemplateParams,
                                 Param->template_arguments(),
                                 SpecArg->template_arguments(), Info, Deduced,
                                 /*NumberOfArgumentsMustMatch=*/false);
}

// If the argument type is a class template specialization, we
// perform template argument deduction using its template
// arguments.
const RecordType *RecordArg = dyn_cast<RecordType>(Arg);
if (!RecordArg) {
  Info.FirstArg = TemplateArgument(QualType(Param, 0));
  Info.SecondArg = TemplateArgument(Arg);
  return Sema::TDK_NonDeducedMismatch;
}

ClassTemplateSpecializationDecl *SpecArg
  = dyn_cast<ClassTemplateSpecializationDecl>(RecordArg->getDecl());
if (!SpecArg) {
  Info.FirstArg = TemplateArgument(QualType(Param, 0));
  Info.SecondArg = TemplateArgument(Arg);
  return Sema::TDK_NonDeducedMismatch;
}

// Perform template argument deduction for the template name.
if (Sema::TemplateDeductionResult Result
      = DeduceTemplateArguments(S,
                                TemplateParams,
                                Param->getTemplateName(),
                             TemplateName(SpecArg->getSpecializedTemplate()),
                                Info, Deduced))
  return Result;

// Perform template argument deduction for the template arguments.
return DeduceTemplateArguments(S, TemplateParams, Param->template_arguments(),
                               SpecArg->getTemplateArgs().asArray(), Info,
                               Deduced, /*NumberOfArgumentsMustMatch=*/true);
626}

628/// Determines whether the given type is an opaque type that
629/// might be more qualified when instantiated.
630static bool IsPossiblyOpaquelyQualifiedType(QualType T) {
switch (T->getTypeClass()) {
case Type::TypeOfExpr:
case Type::TypeOf:
case Type::DependentName:
case Type::Decltype:
case Type::UnresolvedUsing:
case Type::TemplateTypeParm:
  return true;

case Type::ConstantArray:
case Type::IncompleteArray:
case Type::VariableArray:
case Type::DependentSizedArray:
  return IsPossiblyOpaquelyQualifiedType(
                                    cast<ArrayType>(T)->getElementType());

default:
  return false;
}
650}

652/// Helper function to build a TemplateParameter when we don't
653/// know its type statically.
654static TemplateParameter makeTemplateParameter(Decl *D) {
if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(D))
  return TemplateParameter(TTP);
if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(D))
  return TemplateParameter(NTTP);

return TemplateParameter(cast<TemplateTemplateParmDecl>(D));
661}

663/// A pack that we're currently deducing.
664struct clang::DeducedPack {
// The index of the pack.
unsigned Index;

// The old value of the pack before we started deducing it.
DeducedTemplateArgument Saved;

// A deferred value of this pack from an inner deduction, that couldn't be
// deduced because this deduction hadn't happened yet.
DeducedTemplateArgument DeferredDeduction;

// The new value of the pack.
SmallVector<DeducedTemplateArgument, 4> New;

// The outer deduction for this pack, if any.
DeducedPack *Outer = nullptr;

DeducedPack(unsigned Index) : Index(Index) {}
682};

684namespace {

686/// A scope in which we're performing pack deduction.
687class PackDeductionScope {
688public:
/// Prepare to deduce the packs named within Pattern.
PackDeductionScope(Sema &S, TemplateParameterList *TemplateParams,
                   SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                   TemplateDeductionInfo &Info, TemplateArgument Pattern)
    : S(S), TemplateParams(TemplateParams), Deduced(Deduced), Info(Info) {
  unsigned NumNamedPacks = addPacks(Pattern);
  finishConstruction(NumNamedPacks);
}

/// Prepare to directly deduce arguments of the parameter with index \p Index.
PackDeductionScope(Sema &S, TemplateParameterList *TemplateParams,
                   SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                   TemplateDeductionInfo &Info, unsigned Index)
    : S(S), TemplateParams(TemplateParams), Deduced(Deduced), Info(Info) {
  addPack(Index);
  finishConstruction(1);
}

707private:
void addPack(unsigned Index) {
  // Save the deduced template argument for the parameter pack expanded
  // by this pack expansion, then clear out the deduction.
  DeducedPack Pack(Index);
  Pack.Saved = Deduced[Index];
  Deduced[Index] = TemplateArgument();

  // FIXME: What if we encounter multiple packs with different numbers of
  // pre-expanded expansions? (This should already have been diagnosed
  // during substitution.)
  if (Optional<unsigned> ExpandedPackExpansions =
          getExpandedPackSize(TemplateParams->getParam(Index)))
    FixedNumExpansions = ExpandedPackExpansions;

  Packs.push_back(Pack);
}

unsigned addPacks(TemplateArgument Pattern) {
  // Compute the set of template parameter indices that correspond to
  // parameter packs expanded by the pack expansion.
  llvm::SmallBitVector SawIndices(TemplateParams->size());
  llvm::SmallVector<TemplateArgument, 4> ExtraDeductions;

  auto AddPack = [&](unsigned Index) {
    if (SawIndices[Index])
      return;
    SawIndices[Index] = true;
    addPack(Index);

    // Deducing a parameter pack that is a pack expansion also constrains the
    // packs appearing in that parameter to have the same deduced arity. Also,
    // in C++17 onwards, deducing a non-type template parameter deduces its
    // type, so we need to collect the pending deduced values for those packs.
    if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(
            TemplateParams->getParam(Index))) {
      if (!NTTP->isExpandedParameterPack())
        if (auto *Expansion = dyn_cast<PackExpansionType>(NTTP->getType()))
          ExtraDeductions.push_back(Expansion->getPattern());
    }
    // FIXME: Also collect the unexpanded packs in any type and template
    // parameter packs that are pack expansions.
  };

  auto Collect = [&](TemplateArgument Pattern) {
    SmallVector<UnexpandedParameterPack, 2> Unexpanded;
    S.collectUnexpandedParameterPacks(Pattern, Unexpanded);
    for (unsigned I = 0, N = Unexpanded.size(); I != N; ++I) {
      unsigned Depth, Index;
      std::tie(Depth, Index) = getDepthAndIndex(Unexpanded[I]);
      if (Depth == Info.getDeducedDepth())
        AddPack(Index);
    }
  };

  // Look for unexpanded packs in the pattern.
  Collect(Pattern);
  assert(!Packs.empty() && "Pack expansion without unexpanded packs?")((void)0);

  unsigned NumNamedPacks = Packs.size();

  // Also look for unexpanded packs that are indirectly deduced by deducing
  // the sizes of the packs in this pattern.
  while (!ExtraDeductions.empty())
    Collect(ExtraDeductions.pop_back_val());

  return NumNamedPacks;
}

void finishConstruction(unsigned NumNamedPacks) {
  // Dig out the partially-substituted pack, if there is one.
  const TemplateArgument *PartialPackArgs = nullptr;
  unsigned NumPartialPackArgs = 0;
  std::pair<unsigned, unsigned> PartialPackDepthIndex(-1u, -1u);
  if (auto *Scope = S.CurrentInstantiationScope)
    if (auto *Partial = Scope->getPartiallySubstitutedPack(
            &PartialPackArgs, &NumPartialPackArgs))
      PartialPackDepthIndex = getDepthAndIndex(Partial);

  // This pack expansion will have been partially or fully expanded if
  // it only names explicitly-specified parameter packs (including the
  // partially-substituted one, if any).
  bool IsExpanded = true;
  for (unsigned I = 0; I != NumNamedPacks; ++I) {
    if (Packs[I].Index >= Info.getNumExplicitArgs()) {
      IsExpanded = false;
      IsPartiallyExpanded = false;
      break;
    }
    if (PartialPackDepthIndex ==
          std::make_pair(Info.getDeducedDepth(), Packs[I].Index)) {
      IsPartiallyExpanded = true;
    }
  }

  // Skip over the pack elements that were expanded into separate arguments.
  // If we partially expanded, this is the number of partial arguments.
  if (IsPartiallyExpanded)
    PackElements += NumPartialPackArgs;
  else if (IsExpanded)
    PackElements += *FixedNumExpansions;

  for (auto &Pack : Packs) {
    if (Info.PendingDeducedPacks.size() > Pack.Index)
      Pack.Outer = Info.PendingDeducedPacks[Pack.Index];
    else
      Info.PendingDeducedPacks.resize(Pack.Index + 1);
    Info.PendingDeducedPacks[Pack.Index] = &Pack;

    if (PartialPackDepthIndex ==
          std::make_pair(Info.getDeducedDepth(), Pack.Index)) {
      Pack.New.append(PartialPackArgs, PartialPackArgs + NumPartialPackArgs);
      // We pre-populate the deduced value of the partially-substituted
      // pack with the specified value. This is not entirely correct: the
      // value is supposed to have been substituted, not deduced, but the
      // cases where this is observable require an exact type match anyway.
      //
      // FIXME: If we could represent a "depth i, index j, pack elem k"
      // parameter, we could substitute the partially-substituted pack
      // everywhere and avoid this.
      if (!IsPartiallyExpanded)
        Deduced[Pack.Index] = Pack.New[PackElements];
    }
  }
}

833public:
~PackDeductionScope() {
  for (auto &Pack : Packs)
    Info.PendingDeducedPacks[Pack.Index] = Pack.Outer;
}

/// Determine whether this pack has already been partially expanded into a
/// sequence of (prior) function parameters / template arguments.
bool isPartiallyExpanded() { return IsPartiallyExpanded; }

/// Determine whether this pack expansion scope has a known, fixed arity.
/// This happens if it involves a pack from an outer template that has
/// (notionally) already been expanded.
bool hasFixedArity() { return FixedNumExpansions.hasValue(); }

/// Determine whether the next element of the argument is still part of this
/// pack. This is the case unless the pack is already expanded to a fixed
/// length.
bool hasNextElement() {
  return !FixedNumExpansions || *FixedNumExpansions > PackElements;
}

/// Move to deducing the next element in each pack that is being deduced.
void nextPackElement() {
  // Capture the deduced template arguments for each parameter pack expanded
  // by this pack expansion, add them to the list of arguments we've deduced
  // for that pack, then clear out the deduced argument.
  for (auto &Pack : Packs) {
    DeducedTemplateArgument &DeducedArg = Deduced[Pack.Index];
    if (!Pack.New.empty() || !DeducedArg.isNull()) {
      while (Pack.New.size() < PackElements)
        Pack.New.push_back(DeducedTemplateArgument());
      if (Pack.New.size() == PackElements)
        Pack.New.push_back(DeducedArg);
      else
        Pack.New[PackElements] = DeducedArg;
      DeducedArg = Pack.New.size() > PackElements + 1
                       ? Pack.New[PackElements + 1]
                       : DeducedTemplateArgument();
    }
  }
  ++PackElements;
}

/// Finish template argument deduction for a set of argument packs,
/// producing the argument packs and checking for consistency with prior
/// deductions.
Sema::TemplateDeductionResult finish() {
  // Build argument packs for each of the parameter packs expanded by this
  // pack expansion.
  for (auto &Pack : Packs) {
    // Put back the old value for this pack.
    Deduced[Pack.Index] = Pack.Saved;

    // Always make sure the size of this pack is correct, even if we didn't
    // deduce any values for it.
    //
    // FIXME: This isn't required by the normative wording, but substitution
    // and post-substitution checking will always fail if the arity of any
    // pack is not equal to the number of elements we processed. (Either that
    // or something else has gone *very* wrong.) We're permitted to skip any
    // hard errors from those follow-on steps by the intent (but not the
    // wording) of C++ [temp.inst]p8:
    //
    //   If the function selected by overload resolution can be determined
    //   without instantiating a class template definition, it is unspecified
    //   whether that instantiation actually takes place
    Pack.New.resize(PackElements);

    // Build or find a new value for this pack.
    DeducedTemplateArgument NewPack;
    if (Pack.New.empty()) {
      // If we deduced an empty argument pack, create it now.
      NewPack = DeducedTemplateArgument(TemplateArgument::getEmptyPack());
    } else {
      TemplateArgument *ArgumentPack =
          new (S.Context) TemplateArgument[Pack.New.size()];
      std::copy(Pack.New.begin(), Pack.New.end(), ArgumentPack);
      NewPack = DeducedTemplateArgument(
          TemplateArgument(llvm::makeArrayRef(ArgumentPack, Pack.New.size())),
          // FIXME: This is wrong, it's possible that some pack elements are
          // deduced from an array bound and others are not:
          //   template<typename ...T, T ...V> void g(const T (&...p)[V]);
          //   g({1, 2, 3}, {{}, {}});
          // ... should deduce T = {int, size_t (from array bound)}.
          Pack.New[0].wasDeducedFromArrayBound());
    }

    // Pick where we're going to put the merged pack.
    DeducedTemplateArgument *Loc;
    if (Pack.Outer) {
      if (Pack.Outer->DeferredDeduction.isNull()) {
        // Defer checking this pack until we have a complete pack to compare
        // it against.
        Pack.Outer->DeferredDeduction = NewPack;
        continue;
      }
      Loc = &Pack.Outer->DeferredDeduction;
    } else {
      Loc = &Deduced[Pack.Index];
    }

    // Check the new pack matches any previous value.
    DeducedTemplateArgument OldPack = *Loc;
    DeducedTemplateArgument Result =
        checkDeducedTemplateArguments(S.Context, OldPack, NewPack);

    // If we deferred a deduction of this pack, check that one now too.
    if (!Result.isNull() && !Pack.DeferredDeduction.isNull()) {
      OldPack = Result;
      NewPack = Pack.DeferredDeduction;
      Result = checkDeducedTemplateArguments(S.Context, OldPack, NewPack);
    }

    NamedDecl *Param = TemplateParams->getParam(Pack.Index);
    if (Result.isNull()) {
      Info.Param = makeTemplateParameter(Param);
      Info.FirstArg = OldPack;
      Info.SecondArg = NewPack;
      return Sema::TDK_Inconsistent;
    }

    // If we have a pre-expanded pack and we didn't deduce enough elements
    // for it, fail deduction.
    if (Optional<unsigned> Expansions = getExpandedPackSize(Param)) {
      if (*Expansions != PackElements) {
        Info.Param = makeTemplateParameter(Param);
        Info.FirstArg = Result;
        return Sema::TDK_IncompletePack;
      }
    }

    *Loc = Result;
  }

  return Sema::TDK_Success;
}

971private:
Sema &S;
TemplateParameterList *TemplateParams;
SmallVectorImpl<DeducedTemplateArgument> &Deduced;
TemplateDeductionInfo &Info;
unsigned PackElements = 0;
bool IsPartiallyExpanded = false;
/// The number of expansions, if we have a fully-expanded pack in this scope.
Optional<unsigned> FixedNumExpansions;

SmallVector<DeducedPack, 2> Packs;
982};

984} // namespace

986/// Deduce the template arguments by comparing the list of parameter
987/// types to the list of argument types, as in the parameter-type-lists of
988/// function types (C++ [temp.deduct.type]p10).
989///
990/// \param S The semantic analysis object within which we are deducing
991///
992/// \param TemplateParams The template parameters that we are deducing
993///
994/// \param Params The list of parameter types
995///
996/// \param NumParams The number of types in \c Params
997///
998/// \param Args The list of argument types
999///
1000/// \param NumArgs The number of types in \c Args
1001///
1002/// \param Info information about the template argument deduction itself
1003///
1004/// \param Deduced the deduced template arguments
1005///
1006/// \param TDF bitwise OR of the TemplateDeductionFlags bits that describe
1007/// how template argument deduction is performed.
1008///
1009/// \param PartialOrdering If true, we are performing template argument
1010/// deduction for during partial ordering for a call
1011/// (C++0x [temp.deduct.partial]).
1012///
1013/// \returns the result of template argument deduction so far. Note that a
1014/// "success" result means that template argument deduction has not yet failed,
1015/// but it may still fail, later, for other reasons.
1016static Sema::TemplateDeductionResult
1017DeduceTemplateArguments(Sema &S,
                      TemplateParameterList *TemplateParams,
                      const QualType *Params, unsigned NumParams,
                      const QualType *Args, unsigned NumArgs,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                      unsigned TDF,
                      bool PartialOrdering = false) {
// C++0x [temp.deduct.type]p10:
//   Similarly, if P has a form that contains (T), then each parameter type
//   Pi of the respective parameter-type- list of P is compared with the
//   corresponding parameter type Ai of the corresponding parameter-type-list
//   of A. [...]
unsigned ArgIdx = 0, ParamIdx = 0;
for (; ParamIdx != NumParams; ++ParamIdx) {
  // Check argument types.
  const PackExpansionType *Expansion
                              = dyn_cast<PackExpansionType>(Params[ParamIdx]);
  if (!Expansion) {
    // Simple case: compare the parameter and argument types at this point.

    // Make sure we have an argument.
    if (ArgIdx >= NumArgs)
      return Sema::TDK_MiscellaneousDeductionFailure;

    if (isa<PackExpansionType>(Args[ArgIdx])) {
      // C++0x [temp.deduct.type]p22:
      //   If the original function parameter associated with A is a function
      //   parameter pack and the function parameter associated with P is not
      //   a function parameter pack, then template argument deduction fails.
      return Sema::TDK_MiscellaneousDeductionFailure;
    }

    if (Sema::TemplateDeductionResult Result
          = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                               Params[ParamIdx], Args[ArgIdx],
                                               Info, Deduced, TDF,
                                               PartialOrdering))
      return Result;

    ++ArgIdx;
    continue;
  }

  // C++0x [temp.deduct.type]p10:
  //   If the parameter-declaration corresponding to Pi is a function
  //   parameter pack, then the type of its declarator- id is compared with
  //   each remaining parameter type in the parameter-type-list of A. Each
  //   comparison deduces template arguments for subsequent positions in the
  //   template parameter packs expanded by the function parameter pack.

  QualType Pattern = Expansion->getPattern();
  PackDeductionScope PackScope(S, TemplateParams, Deduced, Info, Pattern);

  // A pack scope with fixed arity is not really a pack any more, so is not
  // a non-deduced context.
  if (ParamIdx + 1 == NumParams || PackScope.hasFixedArity()) {
    for (; ArgIdx < NumArgs && PackScope.hasNextElement(); ++ArgIdx) {
      // Deduce template arguments from the pattern.
      if (Sema::TemplateDeductionResult Result
            = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams, Pattern,
                                                 Args[ArgIdx], Info, Deduced,
                                                 TDF, PartialOrdering))
        return Result;

      PackScope.nextPackElement();
    }
  } else {
    // C++0x [temp.deduct.type]p5:
    //   The non-deduced contexts are:
    //     - A function parameter pack that does not occur at the end of the
    //       parameter-declaration-clause.
    //
    // FIXME: There is no wording to say what we should do in this case. We
    // choose to resolve this by applying the same rule that is applied for a
    // function call: that is, deduce all contained packs to their
    // explicitly-specified values (or to <> if there is no such value).
    //
    // This is seemingly-arbitrarily different from the case of a template-id
    // with a non-trailing pack-expansion in its arguments, which renders the
    // entire template-argument-list a non-deduced context.

    // If the parameter type contains an explicitly-specified pack that we
    // could not expand, skip the number of parameters notionally created
    // by the expansion.
    Optional<unsigned> NumExpansions = Expansion->getNumExpansions();
    if (NumExpansions && !PackScope.isPartiallyExpanded()) {
      for (unsigned I = 0; I != *NumExpansions && ArgIdx < NumArgs;
           ++I, ++ArgIdx)
        PackScope.nextPackElement();
    }
  }

  // Build argument packs for each of the parameter packs expanded by this
  // pack expansion.
  if (auto Result = PackScope.finish())
    return Result;
}

// Make sure we don't have any extra arguments.
if (ArgIdx < NumArgs)
  return Sema::TDK_MiscellaneousDeductionFailure;

return Sema::TDK_Success;
1121}

1123/// Determine whether the parameter has qualifiers that the argument
1124/// lacks. Put another way, determine whether there is no way to add
1125/// a deduced set of qualifiers to the ParamType that would result in
1126/// its qualifiers matching those of the ArgType.
1127static bool hasInconsistentOrSupersetQualifiersOf(QualType ParamType,
                                                QualType ArgType) {
Qualifiers ParamQs = ParamType.getQualifiers();
Qualifiers ArgQs = ArgType.getQualifiers();

if (ParamQs == ArgQs)
  return false;

// Mismatched (but not missing) Objective-C GC attributes.
if (ParamQs.getObjCGCAttr() != ArgQs.getObjCGCAttr() &&
    ParamQs.hasObjCGCAttr())
  return true;

// Mismatched (but not missing) address spaces.
if (ParamQs.getAddressSpace() != ArgQs.getAddressSpace() &&
    ParamQs.hasAddressSpace())
  return true;

// Mismatched (but not missing) Objective-C lifetime qualifiers.
if (ParamQs.getObjCLifetime() != ArgQs.getObjCLifetime() &&
    ParamQs.hasObjCLifetime())
  return true;

// CVR qualifiers inconsistent or a superset.
return (ParamQs.getCVRQualifiers() & ~ArgQs.getCVRQualifiers()) != 0;
1152}

1154/// Compare types for equality with respect to possibly compatible
1155/// function types (noreturn adjustment, implicit calling conventions). If any
1156/// of parameter and argument is not a function, just perform type comparison.
1157///
1158/// \param Param the template parameter type.
1159///
1160/// \param Arg the argument type.
1161bool Sema::isSameOrCompatibleFunctionType(CanQualType Param,
                                        CanQualType Arg) {
const FunctionType *ParamFunction = Param->getAs<FunctionType>(),
                   *ArgFunction   = Arg->getAs<FunctionType>();

// Just compare if not functions.
if (!ParamFunction || !ArgFunction)
  return Param == Arg;

// Noreturn and noexcept adjustment.
QualType AdjustedParam;
if (IsFunctionConversion(Param, Arg, AdjustedParam))
  return Arg == Context.getCanonicalType(AdjustedParam);

// FIXME: Compatible calling conventions.

return Param == Arg;
1178}

1180/// Get the index of the first template parameter that was originally from the
1181/// innermost template-parameter-list. This is 0 except when we concatenate
1182/// the template parameter lists of a class template and a constructor template
1183/// when forming an implicit deduction guide.
1184static unsigned getFirstInnerIndex(FunctionTemplateDecl *FTD) {
auto *Guide = dyn_cast<CXXDeductionGuideDecl>(FTD->getTemplatedDecl());
if (!Guide || !Guide->isImplicit())
  return 0;
return Guide->getDeducedTemplate()->getTemplateParameters()->size();
1189}

1191/// Determine whether a type denotes a forwarding reference.
1192static bool isForwardingReference(QualType Param, unsigned FirstInnerIndex) {
// C++1z [temp.deduct.call]p3:
//   A forwarding reference is an rvalue reference to a cv-unqualified
//   template parameter that does not represent a template parameter of a
//   class template.
if (auto *ParamRef = Param->getAs<RValueReferenceType>()) {
  if (ParamRef->getPointeeType().getQualifiers())
    return false;
  auto *TypeParm = ParamRef->getPointeeType()->getAs<TemplateTypeParmType>();
  return TypeParm && TypeParm->getIndex() >= FirstInnerIndex;
}
return false;
1204}

1206///  Attempt to deduce the template arguments by checking the base types
1207///  according to (C++20 [temp.deduct.call] p4b3.
1208///
1209/// \param S the semantic analysis object within which we are deducing.
1210///
1211/// \param RecordT the top level record object we are deducing against.
1212///
1213/// \param TemplateParams the template parameters that we are deducing.
1214///
1215/// \param SpecParam the template specialization parameter type.
1216///
1217/// \param Info information about the template argument deduction itself.
1218///
1219/// \param Deduced the deduced template arguments.
1220///
1221/// \returns the result of template argument deduction with the bases. "invalid"
1222/// means no matches, "success" found a single item, and the
1223/// "MiscellaneousDeductionFailure" result happens when the match is ambiguous.
1224static Sema::TemplateDeductionResult DeduceTemplateBases(
  Sema &S, const RecordType *RecordT, TemplateParameterList *TemplateParams,
  const TemplateSpecializationType *SpecParam, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
// C++14 [temp.deduct.call] p4b3:
//   If P is a class and P has the form simple-template-id, then the
//   transformed A can be a derived class of the deduced A. Likewise if
//   P is a pointer to a class of the form simple-template-id, the
//   transformed A can be a pointer to a derived class pointed to by the
//   deduced A. However, if there is a class C that is a (direct or
//   indirect) base class of D and derived (directly or indirectly) from a
//   class B and that would be a valid deduced A, the deduced A cannot be
//   B or pointer to B, respectively.
//
//   These alternatives are considered only if type deduction would
//   otherwise fail. If they yield more than one possible deduced A, the
//   type deduction fails.

// Use a breadth-first search through the bases to collect the set of
// successful matches. Visited contains the set of nodes we have already
// visited, while ToVisit is our stack of records that we still need to
// visit.  Matches contains a list of matches that have yet to be
// disqualified.
llvm::SmallPtrSet<const RecordType *, 8> Visited;
SmallVector<const RecordType *, 8> ToVisit;
// We iterate over this later, so we have to use MapVector to ensure
// determinism.
llvm::MapVector<const RecordType *, SmallVector<DeducedTemplateArgument, 8>>
    Matches;

auto AddBases = [&Visited, &ToVisit](const RecordType *RT) {
  CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
  for (const auto &Base : RD->bases()) {
    assert(Base.getType()->isRecordType() &&((void)0)
           "Base class that isn't a record?")((void)0);
    const RecordType *RT = Base.getType()->getAs<RecordType>();
    if (Visited.insert(RT).second)
      ToVisit.push_back(Base.getType()->getAs<RecordType>());
  }
};

// Set up the loop by adding all the bases.
AddBases(RecordT);

// Search each path of bases until we either run into a successful match
// (where all bases of it are invalid), or we run out of bases.
while (!ToVisit.empty()) {
  const RecordType *NextT = ToVisit.pop_back_val();

  SmallVector<DeducedTemplateArgument, 8> DeducedCopy(Deduced.begin(),
                                                      Deduced.end());
  TemplateDeductionInfo BaseInfo(TemplateDeductionInfo::ForBase, Info);
  Sema::TemplateDeductionResult BaseResult =
      DeduceTemplateArguments(S, TemplateParams, SpecParam,
                              QualType(NextT, 0), BaseInfo, DeducedCopy);

  // If this was a successful deduction, add it to the list of matches,
  // otherwise we need to continue searching its bases.
  if (BaseResult == Sema::TDK_Success)
    Matches.insert({NextT, DeducedCopy});
  else
    AddBases(NextT);
}

// At this point, 'Matches' contains a list of seemingly valid bases, however
// in the event that we have more than 1 match, it is possible that the base
// of one of the matches might be disqualified for being a base of another
// valid match. We can count on cyclical instantiations being invalid to
// simplify the disqualifications.  That is, if A & B are both matches, and B
// inherits from A (disqualifying A), we know that A cannot inherit from B.
if (Matches.size() > 1) {
  Visited.clear();
  for (const auto &Match : Matches)
    AddBases(Match.first);

  // We can give up once we have a single item (or have run out of things to
  // search) since cyclical inheritence isn't valid.
  while (Matches.size() > 1 && !ToVisit.empty()) {
    const RecordType *NextT = ToVisit.pop_back_val();
    Matches.erase(NextT);

    // Always add all bases, since the inheritence tree can contain
    // disqualifications for multiple matches.
    AddBases(NextT);
  }
}

if (Matches.empty())
  return Sema::TDK_Invalid;
if (Matches.size() > 1)
  return Sema::TDK_MiscellaneousDeductionFailure;

std::swap(Matches.front().second, Deduced);
return Sema::TDK_Success;
1318}

1320/// Deduce the template arguments by comparing the parameter type and
1321/// the argument type (C++ [temp.deduct.type]).
1322///
1323/// \param S the semantic analysis object within which we are deducing
1324///
1325/// \param TemplateParams the template parameters that we are deducing
1326///
1327/// \param ParamIn the parameter type
1328///
1329/// \param ArgIn the argument type
1330///
1331/// \param Info information about the template argument deduction itself
1332///
1333/// \param Deduced the deduced template arguments
1334///
1335/// \param TDF bitwise OR of the TemplateDeductionFlags bits that describe
1336/// how template argument deduction is performed.
1337///
1338/// \param PartialOrdering Whether we're performing template argument deduction
1339/// in the context of partial ordering (C++0x [temp.deduct.partial]).
1340///
1341/// \returns the result of template argument deduction so far. Note that a
1342/// "success" result means that template argument deduction has not yet failed,
1343/// but it may still fail, later, for other reasons.
1344static Sema::TemplateDeductionResult
1345DeduceTemplateArgumentsByTypeMatch(Sema &S,
                                 TemplateParameterList *TemplateParams,
                                 QualType ParamIn, QualType ArgIn,
                                 TemplateDeductionInfo &Info,
                          SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                                 unsigned TDF,
                                 bool PartialOrdering,
                                 bool DeducedFromArrayBound) {
// We only want to look at the canonical types, since typedefs and
// sugar are not part of template argument deduction.
QualType Param = S.Context.getCanonicalType(ParamIn);
QualType Arg = S.Context.getCanonicalType(ArgIn);

// If the argument type is a pack expansion, look at its pattern.
// This isn't explicitly called out
if (const PackExpansionType *ArgExpansion
                                          = dyn_cast<PackExpansionType>(Arg))
  Arg = ArgExpansion->getPattern();

if (PartialOrdering) {
  // C++11 [temp.deduct.partial]p5:
  //   Before the partial ordering is done, certain transformations are
  //   performed on the types used for partial ordering:
  //     - If P is a reference type, P is replaced by the type referred to.
  const ReferenceType *ParamRef = Param->getAs<ReferenceType>();
  if (ParamRef)
    Param = ParamRef->getPointeeType();

  //     - If A is a reference type, A is replaced by the type referred to.
  const ReferenceType *ArgRef = Arg->getAs<ReferenceType>();
  if (ArgRef)
    Arg = ArgRef->getPointeeType();

  if (ParamRef && ArgRef && S.Context.hasSameUnqualifiedType(Param, Arg)) {
    // C++11 [temp.deduct.partial]p9:
    //   If, for a given type, deduction succeeds in both directions (i.e.,
    //   the types are identical after the transformations above) and both
    //   P and A were reference types [...]:
    //     - if [one type] was an lvalue reference and [the other type] was
    //       not, [the other type] is not considered to be at least as
    //       specialized as [the first type]
    //     - if [one type] is more cv-qualified than [the other type],
    //       [the other type] is not considered to be at least as specialized
    //       as [the first type]
    // Objective-C ARC adds:
    //     - [one type] has non-trivial lifetime, [the other type] has
    //       __unsafe_unretained lifetime, and the types are otherwise
    //       identical
    //
    // A is "considered to be at least as specialized" as P iff deduction
    // succeeds, so we model this as a deduction failure. Note that
    // [the first type] is P and [the other type] is A here; the standard
    // gets this backwards.
    Qualifiers ParamQuals = Param.getQualifiers();
    Qualifiers ArgQuals = Arg.getQualifiers();
    if ((ParamRef->isLValueReferenceType() &&
         !ArgRef->isLValueReferenceType()) ||
        ParamQuals.isStrictSupersetOf(ArgQuals) ||
        (ParamQuals.hasNonTrivialObjCLifetime() &&
         ArgQuals.getObjCLifetime() == Qualifiers::OCL_ExplicitNone &&
         ParamQuals.withoutObjCLifetime() ==
             ArgQuals.withoutObjCLifetime())) {
      Info.FirstArg = TemplateArgument(ParamIn);
      Info.SecondArg = TemplateArgument(ArgIn);
      return Sema::TDK_NonDeducedMismatch;
    }
  }

  // C++11 [temp.deduct.partial]p7:
  //   Remove any top-level cv-qualifiers:
  //     - If P is a cv-qualified type, P is replaced by the cv-unqualified
  //       version of P.
  Param = Param.getUnqualifiedType();
  //     - If A is a cv-qualified type, A is replaced by the cv-unqualified
  //       version of A.
  Arg = Arg.getUnqualifiedType();
} else {
  // C++0x [temp.deduct.call]p4 bullet 1:
  //   - If the original P is a reference type, the deduced A (i.e., the type
  //     referred to by the reference) can be more cv-qualified than the
  //     transformed A.
  if (TDF & TDF_ParamWithReferenceType) {
    Qualifiers Quals;
    QualType UnqualParam = S.Context.getUnqualifiedArrayType(Param, Quals);
    Quals.setCVRQualifiers(Quals.getCVRQualifiers() &
                           Arg.getCVRQualifiers());
    Param = S.Context.getQualifiedType(UnqualParam, Quals);
  }

  if ((TDF & TDF_TopLevelParameterTypeList) && !Param->isFunctionType()) {
    // C++0x [temp.deduct.type]p10:
    //   If P and A are function types that originated from deduction when
    //   taking the address of a function template (14.8.2.2) or when deducing
    //   template arguments from a function declaration (14.8.2.6) and Pi and
    //   Ai are parameters of the top-level parameter-type-list of P and A,
    //   respectively, Pi is adjusted if it is a forwarding reference and Ai
    //   is an lvalue reference, in
    //   which case the type of Pi is changed to be the template parameter
    //   type (i.e., T&& is changed to simply T). [ Note: As a result, when
    //   Pi is T&& and Ai is X&, the adjusted Pi will be T, causing T to be
    //   deduced as X&. - end note ]
    TDF &= ~TDF_TopLevelParameterTypeList;
    if (isForwardingReference(Param, 0) && Arg->isLValueReferenceType())
      Param = Param->getPointeeType();
  }
}

// C++ [temp.deduct.type]p9:
//   A template type argument T, a template template argument TT or a
//   template non-type argument i can be deduced if P and A have one of
//   the following forms:
//
//     T
//     cv-list T
if (const TemplateTypeParmType *TemplateTypeParm
      = Param->getAs<TemplateTypeParmType>()) {
  // Just skip any attempts to deduce from a placeholder type or a parameter
  // at a different depth.
  if (Arg->isPlaceholderType() ||
      Info.getDeducedDepth() != TemplateTypeParm->getDepth())
    return Sema::TDK_Success;

  unsigned Index = TemplateTypeParm->getIndex();
  bool RecanonicalizeArg = false;

  // If the argument type is an array type, move the qualifiers up to the
  // top level, so they can be matched with the qualifiers on the parameter.
  if (isa<ArrayType>(Arg)) {
    Qualifiers Quals;
    Arg = S.Context.getUnqualifiedArrayType(Arg, Quals);
    if (Quals) {
      Arg = S.Context.getQualifiedType(Arg, Quals);
      RecanonicalizeArg = true;
    }
  }

  // The argument type can not be less qualified than the parameter
  // type.
  if (!(TDF & TDF_IgnoreQualifiers) &&
      hasInconsistentOrSupersetQualifiersOf(Param, Arg)) {
    Info.Param = cast<TemplateTypeParmDecl>(TemplateParams->getParam(Index));
    Info.FirstArg = TemplateArgument(Param);
    Info.SecondArg = TemplateArgument(Arg);
    return Sema::TDK_Underqualified;
  }

  // Do not match a function type with a cv-qualified type.
  // http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1584
  if (Arg->isFunctionType() && Param.hasQualifiers()) {
    return Sema::TDK_NonDeducedMismatch;
  }

  assert(TemplateTypeParm->getDepth() == Info.getDeducedDepth() &&((void)0)
         "saw template type parameter with wrong depth")((void)0);
  assert(Arg != S.Context.OverloadTy && "Unresolved overloaded function")((void)0);
  QualType DeducedType = Arg;

  // Remove any qualifiers on the parameter from the deduced type.
  // We checked the qualifiers for consistency above.
  Qualifiers DeducedQs = DeducedType.getQualifiers();
  Qualifiers ParamQs = Param.getQualifiers();
  DeducedQs.removeCVRQualifiers(ParamQs.getCVRQualifiers());
  if (ParamQs.hasObjCGCAttr())
    DeducedQs.removeObjCGCAttr();
  if (ParamQs.hasAddressSpace())
    DeducedQs.removeAddressSpace();
  if (ParamQs.hasObjCLifetime())
    DeducedQs.removeObjCLifetime();

  // Objective-C ARC:
  //   If template deduction would produce a lifetime qualifier on a type
  //   that is not a lifetime type, template argument deduction fails.
  if (ParamQs.hasObjCLifetime() && !DeducedType->isObjCLifetimeType() &&
      !DeducedType->isDependentType()) {
    Info.Param = cast<TemplateTypeParmDecl>(TemplateParams->getParam(Index));
    Info.FirstArg = TemplateArgument(Param);
    Info.SecondArg = TemplateArgument(Arg);
    return Sema::TDK_Underqualified;
  }

  // Objective-C ARC:
  //   If template deduction would produce an argument type with lifetime type
  //   but no lifetime qualifier, the __strong lifetime qualifier is inferred.
  if (S.getLangOpts().ObjCAutoRefCount &&
      DeducedType->isObjCLifetimeType() &&
      !DeducedQs.hasObjCLifetime())
    DeducedQs.setObjCLifetime(Qualifiers::OCL_Strong);

  DeducedType = S.Context.getQualifiedType(DeducedType.getUnqualifiedType(),
                                           DeducedQs);

  if (RecanonicalizeArg)
    DeducedType = S.Context.getCanonicalType(DeducedType);

  DeducedTemplateArgument NewDeduced(DeducedType, DeducedFromArrayBound);
  DeducedTemplateArgument Result = checkDeducedTemplateArguments(S.Context,
                                                               Deduced[Index],
                                                                 NewDeduced);
  if (Result.isNull()) {
    Info.Param = cast<TemplateTypeParmDecl>(TemplateParams->getParam(Index));
    Info.FirstArg = Deduced[Index];
    Info.SecondArg = NewDeduced;
    return Sema::TDK_Inconsistent;
  }

  Deduced[Index] = Result;
  return Sema::TDK_Success;
}

// Set up the template argument deduction information for a failure.
Info.FirstArg = TemplateArgument(ParamIn);
Info.SecondArg = TemplateArgument(ArgIn);

// If the parameter is an already-substituted template parameter
// pack, do nothing: we don't know which of its arguments to look
// at, so we have to wait until all of the parameter packs in this
// expansion have arguments.
if (isa<SubstTemplateTypeParmPackType>(Param))
  return Sema::TDK_Success;

// Check the cv-qualifiers on the parameter and argument types.
CanQualType CanParam = S.Context.getCanonicalType(Param);
CanQualType CanArg = S.Context.getCanonicalType(Arg);
if (!(TDF & TDF_IgnoreQualifiers)) {
  if (TDF & TDF_ParamWithReferenceType) {
    if (hasInconsistentOrSupersetQualifiersOf(Param, Arg))
      return Sema::TDK_NonDeducedMismatch;
  } else if (TDF & TDF_ArgWithReferenceType) {
    // C++ [temp.deduct.conv]p4:
    //   If the original A is a reference type, A can be more cv-qualified
    //   than the deduced A
    if (!Arg.getQualifiers().compatiblyIncludes(Param.getQualifiers()))
      return Sema::TDK_NonDeducedMismatch;

    // Strip out all extra qualifiers from the argument to figure out the
    // type we're converting to, prior to the qualification conversion.
    Qualifiers Quals;
    Arg = S.Context.getUnqualifiedArrayType(Arg, Quals);
    Arg = S.Context.getQualifiedType(Arg, Param.getQualifiers());
  } else if (!IsPossiblyOpaquelyQualifiedType(Param)) {
    if (Param.getCVRQualifiers() != Arg.getCVRQualifiers())
      return Sema::TDK_NonDeducedMismatch;
  }

  // If the parameter type is not dependent, there is nothing to deduce.
  if (!Param->isDependentType()) {
    if (!(TDF & TDF_SkipNonDependent)) {
      bool NonDeduced =
          (TDF & TDF_AllowCompatibleFunctionType)
              ? !S.isSameOrCompatibleFunctionType(CanParam, CanArg)
              : Param != Arg;
      if (NonDeduced) {
        return Sema::TDK_NonDeducedMismatch;
      }
    }
    return Sema::TDK_Success;
  }
} else if (!Param->isDependentType()) {
  if (!(TDF & TDF_SkipNonDependent)) {
    CanQualType ParamUnqualType = CanParam.getUnqualifiedType(),
                ArgUnqualType = CanArg.getUnqualifiedType();
    bool Success =
        (TDF & TDF_AllowCompatibleFunctionType)
            ? S.isSameOrCompatibleFunctionType(ParamUnqualType, ArgUnqualType)
            : ParamUnqualType == ArgUnqualType;
    if (Success)
      return Sema::TDK_Success;
  } else {
    return Sema::TDK_Success;
  }
}

switch (Param->getTypeClass()) {
  // Non-canonical types cannot appear here.
1619#define NON_CANONICAL_TYPE(Class, Base) \
case Type::Class: llvm_unreachable("deducing non-canonical type: " #Class)__builtin_unreachable();
1621#define TYPE(Class, Base)
1622#include "clang/AST/TypeNodes.inc"

  case Type::TemplateTypeParm:
  case Type::SubstTemplateTypeParmPack:
    llvm_unreachable("Type nodes handled above")__builtin_unreachable();

  // These types cannot be dependent, so simply check whether the types are
  // the same.
  case Type::Builtin:
  case Type::VariableArray:
  case Type::Vector:
  case Type::FunctionNoProto:
  case Type::Record:
  case Type::Enum:
  case Type::ObjCObject:
  case Type::ObjCInterface:
  case Type::ObjCObjectPointer:
  case Type::ExtInt:
    if (TDF & TDF_SkipNonDependent)
      return Sema::TDK_Success;

    if (TDF & TDF_IgnoreQualifiers) {
      Param = Param.getUnqualifiedType();
      Arg = Arg.getUnqualifiedType();
    }

    return Param == Arg? Sema::TDK_Success : Sema::TDK_NonDeducedMismatch;

  //     _Complex T   [placeholder extension]
  case Type::Complex:
    if (const ComplexType *ComplexArg = Arg->getAs<ComplexType>())
      return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                  cast<ComplexType>(Param)->getElementType(),
                                  ComplexArg->getElementType(),
                                  Info, Deduced, TDF);

    return Sema::TDK_NonDeducedMismatch;

  //     _Atomic T   [extension]
  case Type::Atomic:
    if (const AtomicType *AtomicArg = Arg->getAs<AtomicType>())
      return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                     cast<AtomicType>(Param)->getValueType(),
                                     AtomicArg->getValueType(),
                                     Info, Deduced, TDF);

    return Sema::TDK_NonDeducedMismatch;

  //     T *
  case Type::Pointer: {
    QualType PointeeType;
    if (const PointerType *PointerArg = Arg->getAs<PointerType>()) {
      PointeeType = PointerArg->getPointeeType();
    } else if (const ObjCObjectPointerType *PointerArg
                 = Arg->getAs<ObjCObjectPointerType>()) {
      PointeeType = PointerArg->getPointeeType();
    } else {
      return Sema::TDK_NonDeducedMismatch;
    }

    unsigned SubTDF = TDF & (TDF_IgnoreQualifiers | TDF_DerivedClass);
    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                   cast<PointerType>(Param)->getPointeeType(),
                                   PointeeType,
                                   Info, Deduced, SubTDF);
  }

  //     T &
  case Type::LValueReference: {
    const LValueReferenceType *ReferenceArg =
        Arg->getAs<LValueReferenceType>();
    if (!ReferenceArg)
      return Sema::TDK_NonDeducedMismatch;

    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                         cast<LValueReferenceType>(Param)->getPointeeType(),
                         ReferenceArg->getPointeeType(), Info, Deduced, 0);
  }

  //     T && [C++0x]
  case Type::RValueReference: {
    const RValueReferenceType *ReferenceArg =
        Arg->getAs<RValueReferenceType>();
    if (!ReferenceArg)
      return Sema::TDK_NonDeducedMismatch;

    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                           cast<RValueReferenceType>(Param)->getPointeeType(),
                           ReferenceArg->getPointeeType(),
                           Info, Deduced, 0);
  }

  //     T [] (implied, but not stated explicitly)
  case Type::IncompleteArray: {
    const IncompleteArrayType *IncompleteArrayArg =
      S.Context.getAsIncompleteArrayType(Arg);
    if (!IncompleteArrayArg)
      return Sema::TDK_NonDeducedMismatch;

    unsigned SubTDF = TDF & TDF_IgnoreQualifiers;
    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                  S.Context.getAsIncompleteArrayType(Param)->getElementType(),
                  IncompleteArrayArg->getElementType(),
                  Info, Deduced, SubTDF);
  }

  //     T [integer-constant]
  case Type::ConstantArray: {
    const ConstantArrayType *ConstantArrayArg =
      S.Context.getAsConstantArrayType(Arg);
    if (!ConstantArrayArg)
      return Sema::TDK_NonDeducedMismatch;

    const ConstantArrayType *ConstantArrayParm =
      S.Context.getAsConstantArrayType(Param);
    if (ConstantArrayArg->getSize() != ConstantArrayParm->getSize())
      return Sema::TDK_NonDeducedMismatch;

    unsigned SubTDF = TDF & TDF_IgnoreQualifiers;
    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                         ConstantArrayParm->getElementType(),
                                         ConstantArrayArg->getElementType(),
                                         Info, Deduced, SubTDF);
  }

  //     type [i]
  case Type::DependentSizedArray: {
    const ArrayType *ArrayArg = S.Context.getAsArrayType(Arg);
    if (!ArrayArg)
      return Sema::TDK_NonDeducedMismatch;

    unsigned SubTDF = TDF & TDF_IgnoreQualifiers;

    // Check the element type of the arrays
    const DependentSizedArrayType *DependentArrayParm
      = S.Context.getAsDependentSizedArrayType(Param);
    if (Sema::TemplateDeductionResult Result
          = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                        DependentArrayParm->getElementType(),
                                        ArrayArg->getElementType(),
                                        Info, Deduced, SubTDF))
      return Result;

    // Determine the array bound is something we can deduce.
    const NonTypeTemplateParmDecl *NTTP
      = getDeducedParameterFromExpr(Info, DependentArrayParm->getSizeExpr());
    if (!NTTP)
      return Sema::TDK_Success;

    // We can perform template argument deduction for the given non-type
    // template parameter.
    assert(NTTP->getDepth() == Info.getDeducedDepth() &&((void)0)
           "saw non-type template parameter with wrong depth")((void)0);
    if (const ConstantArrayType *ConstantArrayArg
          = dyn_cast<ConstantArrayType>(ArrayArg)) {
      llvm::APSInt Size(ConstantArrayArg->getSize());
      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP, Size,
                                           S.Context.getSizeType(),
                                           /*ArrayBound=*/true,
                                           Info, Deduced);
    }
    if (const DependentSizedArrayType *DependentArrayArg
          = dyn_cast<DependentSizedArrayType>(ArrayArg))
      if (DependentArrayArg->getSizeExpr())
        return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                             DependentArrayArg->getSizeExpr(),
                                             Info, Deduced);

    // Incomplete type does not match a dependently-sized array type
    return Sema::TDK_NonDeducedMismatch;
  }

  //     type(*)(T)
  //     T(*)()
  //     T(*)(T)
  case Type::FunctionProto: {
    unsigned SubTDF = TDF & TDF_TopLevelParameterTypeList;
    const FunctionProtoType *FunctionProtoArg =
      dyn_cast<FunctionProtoType>(Arg);
    if (!FunctionProtoArg)
      return Sema::TDK_NonDeducedMismatch;

    const FunctionProtoType *FunctionProtoParam =
      cast<FunctionProtoType>(Param);

    if (FunctionProtoParam->getMethodQuals()
          != FunctionProtoArg->getMethodQuals() ||
        FunctionProtoParam->getRefQualifier()
          != FunctionProtoArg->getRefQualifier() ||
        FunctionProtoParam->isVariadic() != FunctionProtoArg->isVariadic())
      return Sema::TDK_NonDeducedMismatch;

    // Check return types.
    if (auto Result = DeduceTemplateArgumentsByTypeMatch(
            S, TemplateParams, FunctionProtoParam->getReturnType(),
            FunctionProtoArg->getReturnType(), Info, Deduced, 0))
      return Result;

    // Check parameter types.
    if (auto Result = DeduceTemplateArguments(
            S, TemplateParams, FunctionProtoParam->param_type_begin(),
            FunctionProtoParam->getNumParams(),
            FunctionProtoArg->param_type_begin(),
            FunctionProtoArg->getNumParams(), Info, Deduced, SubTDF))
      return Result;

    if (TDF & TDF_AllowCompatibleFunctionType)
      return Sema::TDK_Success;

    // FIXME: Per core-2016/10/1019 (no corresponding core issue yet), permit
    // deducing through the noexcept-specifier if it's part of the canonical
    // type. libstdc++ relies on this.
    Expr *NoexceptExpr = FunctionProtoParam->getNoexceptExpr();
    if (const NonTypeTemplateParmDecl *NTTP =
        NoexceptExpr ? getDeducedParameterFromExpr(Info, NoexceptExpr)
                     : nullptr) {
      assert(NTTP->getDepth() == Info.getDeducedDepth() &&((void)0)
             "saw non-type template parameter with wrong depth")((void)0);

      llvm::APSInt Noexcept(1);
      switch (FunctionProtoArg->canThrow()) {
      case CT_Cannot:
        Noexcept = 1;
        LLVM_FALLTHROUGH[[gnu::fallthrough]];

      case CT_Can:
        // We give E in noexcept(E) the "deduced from array bound" treatment.
        // FIXME: Should we?
        return DeduceNonTypeTemplateArgument(
            S, TemplateParams, NTTP, Noexcept, S.Context.BoolTy,
            /*ArrayBound*/true, Info, Deduced);

      case CT_Dependent:
        if (Expr *ArgNoexceptExpr = FunctionProtoArg->getNoexceptExpr())
          return DeduceNonTypeTemplateArgument(
              S, TemplateParams, NTTP, ArgNoexceptExpr, Info, Deduced);
        // Can't deduce anything from throw(T...).
        break;
      }
    }
    // FIXME: Detect non-deduced exception specification mismatches?
    //
    // Careful about [temp.deduct.call] and [temp.deduct.conv], which allow
    // top-level differences in noexcept-specifications.

    return Sema::TDK_Success;
  }

  case Type::InjectedClassName:
    // Treat a template's injected-class-name as if the template
    // specialization type had been used.
    Param = cast<InjectedClassNameType>(Param)
      ->getInjectedSpecializationType();
    assert(isa<TemplateSpecializationType>(Param) &&((void)0)
           "injected class name is not a template specialization type")((void)0);
    LLVM_FALLTHROUGH[[gnu::fallthrough]];

  //     template-name<T> (where template-name refers to a class template)
  //     template-name<i>
  //     TT<T>
  //     TT<i>
  //     TT<>
  case Type::TemplateSpecialization: {
    const TemplateSpecializationType *SpecParam =
        cast<TemplateSpecializationType>(Param);

    // When Arg cannot be a derived class, we can just try to deduce template
    // arguments from the template-id.
    const RecordType *RecordT = Arg->getAs<RecordType>();
    if (!(TDF & TDF_DerivedClass) || !RecordT)
      return DeduceTemplateArguments(S, TemplateParams, SpecParam, Arg, Info,
                                     Deduced);

    SmallVector<DeducedTemplateArgument, 8> DeducedOrig(Deduced.begin(),
                                                        Deduced.end());

    Sema::TemplateDeductionResult Result = DeduceTemplateArguments(
        S, TemplateParams, SpecParam, Arg, Info, Deduced);

    if (Result == Sema::TDK_Success)
      return Result;

    // We cannot inspect base classes as part of deduction when the type
    // is incomplete, so either instantiate any templates necessary to
    // complete the type, or skip over it if it cannot be completed.
    if (!S.isCompleteType(Info.getLocation(), Arg))
      return Result;

    // Reset the incorrectly deduced argument from above.
    Deduced = DeducedOrig;

    // Check bases according to C++14 [temp.deduct.call] p4b3:
    Sema::TemplateDeductionResult BaseResult = DeduceTemplateBases(
        S, RecordT, TemplateParams, SpecParam, Info, Deduced);

    if (BaseResult != Sema::TDK_Invalid)
      return BaseResult;
    return Result;
  }

  //     T type::*
  //     T T::*
  //     T (type::*)()
  //     type (T::*)()
  //     type (type::*)(T)
  //     type (T::*)(T)
  //     T (type::*)(T)
  //     T (T::*)()
  //     T (T::*)(T)
  case Type::MemberPointer: {
    const MemberPointerType *MemPtrParam = cast<MemberPointerType>(Param);
    const MemberPointerType *MemPtrArg = dyn_cast<MemberPointerType>(Arg);
    if (!MemPtrArg)
      return Sema::TDK_NonDeducedMismatch;

    QualType ParamPointeeType = MemPtrParam->getPointeeType();
    if (ParamPointeeType->isFunctionType())
      S.adjustMemberFunctionCC(ParamPointeeType, /*IsStatic=*/true,
                               /*IsCtorOrDtor=*/false, Info.getLocation());
    QualType ArgPointeeType = MemPtrArg->getPointeeType();
    if (ArgPointeeType->isFunctionType())
      S.adjustMemberFunctionCC(ArgPointeeType, /*IsStatic=*/true,
                               /*IsCtorOrDtor=*/false, Info.getLocation());

    if (Sema::TemplateDeductionResult Result
          = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                               ParamPointeeType,
                                               ArgPointeeType,
                                               Info, Deduced,
                                               TDF & TDF_IgnoreQualifiers))
      return Result;

    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                         QualType(MemPtrParam->getClass(), 0),
                                         QualType(MemPtrArg->getClass(), 0),
                                         Info, Deduced,
                                         TDF & TDF_IgnoreQualifiers);
  }

  //     (clang extension)
  //
  //     type(^)(T)
  //     T(^)()
  //     T(^)(T)
  case Type::BlockPointer: {
    const BlockPointerType *BlockPtrParam = cast<BlockPointerType>(Param);
    const BlockPointerType *BlockPtrArg = dyn_cast<BlockPointerType>(Arg);

    if (!BlockPtrArg)
      return Sema::TDK_NonDeducedMismatch;

    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                              BlockPtrParam->getPointeeType(),
                                              BlockPtrArg->getPointeeType(),
                                              Info, Deduced, 0);
  }

  //     (clang extension)
  //
  //     T __attribute__(((ext_vector_type(<integral constant>))))
  case Type::ExtVector: {
    const ExtVectorType *VectorParam = cast<ExtVectorType>(Param);
    if (const ExtVectorType *VectorArg = dyn_cast<ExtVectorType>(Arg)) {
      // Make sure that the vectors have the same number of elements.
      if (VectorParam->getNumElements() != VectorArg->getNumElements())
        return Sema::TDK_NonDeducedMismatch;

      // Perform deduction on the element types.
      return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                                VectorParam->getElementType(),
                                                VectorArg->getElementType(),
                                                Info, Deduced, TDF);
    }

    if (const DependentSizedExtVectorType *VectorArg
                              = dyn_cast<DependentSizedExtVectorType>(Arg)) {
      // We can't check the number of elements, since the argument has a
      // dependent number of elements. This can only occur during partial
      // ordering.

      // Perform deduction on the element types.
      return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                                VectorParam->getElementType(),
                                                VectorArg->getElementType(),
                                                Info, Deduced, TDF);
    }

    return Sema::TDK_NonDeducedMismatch;
  }

  case Type::DependentVector: {
    const auto *VectorParam = cast<DependentVectorType>(Param);

    if (const auto *VectorArg = dyn_cast<VectorType>(Arg)) {
      // Perform deduction on the element types.
      if (Sema::TemplateDeductionResult Result =
              DeduceTemplateArgumentsByTypeMatch(
                  S, TemplateParams, VectorParam->getElementType(),
                  VectorArg->getElementType(), Info, Deduced, TDF))
        return Result;

      // Perform deduction on the vector size, if we can.
      const NonTypeTemplateParmDecl *NTTP =
          getDeducedParameterFromExpr(Info, VectorParam->getSizeExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      llvm::APSInt ArgSize(S.Context.getTypeSize(S.Context.IntTy), false);
      ArgSize = VectorArg->getNumElements();
      // Note that we use the "array bound" rules here; just like in that
      // case, we don't have any particular type for the vector size, but
      // we can provide one if necessary.
      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP, ArgSize,
                                           S.Context.UnsignedIntTy, true,
                                           Info, Deduced);
    }

    if (const auto *VectorArg = dyn_cast<DependentVectorType>(Arg)) {
      // Perform deduction on the element types.
      if (Sema::TemplateDeductionResult Result =
              DeduceTemplateArgumentsByTypeMatch(
                  S, TemplateParams, VectorParam->getElementType(),
                  VectorArg->getElementType(), Info, Deduced, TDF))
        return Result;

      // Perform deduction on the vector size, if we can.
      const NonTypeTemplateParmDecl *NTTP = getDeducedParameterFromExpr(
          Info, VectorParam->getSizeExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      return DeduceNonTypeTemplateArgument(
          S, TemplateParams, NTTP, VectorArg->getSizeExpr(), Info, Deduced);
    }

    return Sema::TDK_NonDeducedMismatch;
  }

  //     (clang extension)
  //
  //     T __attribute__(((ext_vector_type(N))))
  case Type::DependentSizedExtVector: {
    const DependentSizedExtVectorType *VectorParam
      = cast<DependentSizedExtVectorType>(Param);

    if (const ExtVectorType *VectorArg = dyn_cast<ExtVectorType>(Arg)) {
      // Perform deduction on the element types.
      if (Sema::TemplateDeductionResult Result
            = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                                VectorParam->getElementType(),
                                                 VectorArg->getElementType(),
                                                 Info, Deduced, TDF))
        return Result;

      // Perform deduction on the vector size, if we can.
      const NonTypeTemplateParmDecl *NTTP =
          getDeducedParameterFromExpr(Info, VectorParam->getSizeExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      llvm::APSInt ArgSize(S.Context.getTypeSize(S.Context.IntTy), false);
      ArgSize = VectorArg->getNumElements();
      // Note that we use the "array bound" rules here; just like in that
      // case, we don't have any particular type for the vector size, but
      // we can provide one if necessary.
      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP, ArgSize,
                                           S.Context.IntTy, true, Info,
                                           Deduced);
    }

    if (const DependentSizedExtVectorType *VectorArg
                              = dyn_cast<DependentSizedExtVectorType>(Arg)) {
      // Perform deduction on the element types.
      if (Sema::TemplateDeductionResult Result
          = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                               VectorParam->getElementType(),
                                               VectorArg->getElementType(),
                                               Info, Deduced, TDF))
        return Result;

      // Perform deduction on the vector size, if we can.
      const NonTypeTemplateParmDecl *NTTP =
          getDeducedParameterFromExpr(Info, VectorParam->getSizeExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                           VectorArg->getSizeExpr(),
                                           Info, Deduced);
    }

    return Sema::TDK_NonDeducedMismatch;
  }

  //     (clang extension)
  //
  //     T __attribute__((matrix_type(<integral constant>,
  //                                  <integral constant>)))
  case Type::ConstantMatrix: {
    const ConstantMatrixType *MatrixArg = dyn_cast<ConstantMatrixType>(Arg);
    if (!MatrixArg)
      return Sema::TDK_NonDeducedMismatch;

    const ConstantMatrixType *MatrixParam = cast<ConstantMatrixType>(Param);
    // Check that the dimensions are the same
    if (MatrixParam->getNumRows() != MatrixArg->getNumRows() ||
        MatrixParam->getNumColumns() != MatrixArg->getNumColumns()) {
      return Sema::TDK_NonDeducedMismatch;
    }
    // Perform deduction on element types.
    return DeduceTemplateArgumentsByTypeMatch(
        S, TemplateParams, MatrixParam->getElementType(),
        MatrixArg->getElementType(), Info, Deduced, TDF);
  }

  case Type::DependentSizedMatrix: {
    const MatrixType *MatrixArg = dyn_cast<MatrixType>(Arg);
    if (!MatrixArg)
      return Sema::TDK_NonDeducedMismatch;

    // Check the element type of the matrixes.
    const DependentSizedMatrixType *MatrixParam =
        cast<DependentSizedMatrixType>(Param);
    if (Sema::TemplateDeductionResult Result =
            DeduceTemplateArgumentsByTypeMatch(
                S, TemplateParams, MatrixParam->getElementType(),
                MatrixArg->getElementType(), Info, Deduced, TDF))
      return Result;

    // Try to deduce a matrix dimension.
    auto DeduceMatrixArg =
        [&S, &Info, &Deduced, &TemplateParams](
            Expr *ParamExpr, const MatrixType *Arg,
            unsigned (ConstantMatrixType::*GetArgDimension)() const,
            Expr *(DependentSizedMatrixType::*GetArgDimensionExpr)() const) {
          const auto *ArgConstMatrix = dyn_cast<ConstantMatrixType>(Arg);
          const auto *ArgDepMatrix = dyn_cast<DependentSizedMatrixType>(Arg);
          if (!ParamExpr->isValueDependent()) {
            Optional<llvm::APSInt> ParamConst =
                ParamExpr->getIntegerConstantExpr(S.Context);
            if (!ParamConst)
              return Sema::TDK_NonDeducedMismatch;

            if (ArgConstMatrix) {
              if ((ArgConstMatrix->*GetArgDimension)() == *ParamConst)
                return Sema::TDK_Success;
              return Sema::TDK_NonDeducedMismatch;
            }

            Expr *ArgExpr = (ArgDepMatrix->*GetArgDimensionExpr)();
            if (!ArgExpr->isValueDependent())
              if (Optional<llvm::APSInt> ArgConst =
                      ArgExpr->getIntegerConstantExpr(S.Context))
                if (*ArgConst == *ParamConst)
                  return Sema::TDK_Success;
            return Sema::TDK_NonDeducedMismatch;
          }

          const NonTypeTemplateParmDecl *NTTP =
              getDeducedParameterFromExpr(Info, ParamExpr);
          if (!NTTP)
            return Sema::TDK_Success;

          if (ArgConstMatrix) {
            llvm::APSInt ArgConst(
                S.Context.getTypeSize(S.Context.getSizeType()));
            ArgConst = (ArgConstMatrix->*GetArgDimension)();
            return DeduceNonTypeTemplateArgument(
                S, TemplateParams, NTTP, ArgConst, S.Context.getSizeType(),
                /*ArrayBound=*/true, Info, Deduced);
          }

          return DeduceNonTypeTemplateArgument(
              S, TemplateParams, NTTP, (ArgDepMatrix->*GetArgDimensionExpr)(),
              Info, Deduced);
        };

    auto Result = DeduceMatrixArg(MatrixParam->getRowExpr(), MatrixArg,
                                  &ConstantMatrixType::getNumRows,
                                  &DependentSizedMatrixType::getRowExpr);
    if (Result)
      return Result;

    return DeduceMatrixArg(MatrixParam->getColumnExpr(), MatrixArg,
                           &ConstantMatrixType::getNumColumns,
                           &DependentSizedMatrixType::getColumnExpr);
  }

  //     (clang extension)
  //
  //     T __attribute__(((address_space(N))))
  case Type::DependentAddressSpace: {
    const DependentAddressSpaceType *AddressSpaceParam =
        cast<DependentAddressSpaceType>(Param);

    if (const DependentAddressSpaceType *AddressSpaceArg =
            dyn_cast<DependentAddressSpaceType>(Arg)) {
      // Perform deduction on the pointer type.
      if (Sema::TemplateDeductionResult Result =
              DeduceTemplateArgumentsByTypeMatch(
                  S, TemplateParams, AddressSpaceParam->getPointeeType(),
                  AddressSpaceArg->getPointeeType(), Info, Deduced, TDF))
        return Result;

      // Perform deduction on the address space, if we can.
      const NonTypeTemplateParmDecl *NTTP = getDeducedParameterFromExpr(
          Info, AddressSpaceParam->getAddrSpaceExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      return DeduceNonTypeTemplateArgument(
          S, TemplateParams, NTTP, AddressSpaceArg->getAddrSpaceExpr(), Info,
          Deduced);
    }

    if (isTargetAddressSpace(Arg.getAddressSpace())) {
      llvm::APSInt ArgAddressSpace(S.Context.getTypeSize(S.Context.IntTy),
                                   false);
      ArgAddressSpace = toTargetAddressSpace(Arg.getAddressSpace());

      // Perform deduction on the pointer types.
      if (Sema::TemplateDeductionResult Result =
              DeduceTemplateArgumentsByTypeMatch(
                  S, TemplateParams, AddressSpaceParam->getPointeeType(),
                  S.Context.removeAddrSpaceQualType(Arg), Info, Deduced, TDF))
        return Result;

      // Perform deduction on the address space, if we can.
      const NonTypeTemplateParmDecl *NTTP = getDeducedParameterFromExpr(
          Info, AddressSpaceParam->getAddrSpaceExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                           ArgAddressSpace, S.Context.IntTy,
                                           true, Info, Deduced);
    }

    return Sema::TDK_NonDeducedMismatch;
  }
  case Type::DependentExtInt: {
    const auto *IntParam = cast<DependentExtIntType>(Param);

    if (const auto *IntArg = dyn_cast<ExtIntType>(Arg)){
      if (IntParam->isUnsigned() != IntArg->isUnsigned())
        return Sema::TDK_NonDeducedMismatch;

      const NonTypeTemplateParmDecl *NTTP =
          getDeducedParameterFromExpr(Info, IntParam->getNumBitsExpr());
      if (!NTTP)
        return Sema::TDK_Success;

      llvm::APSInt ArgSize(S.Context.getTypeSize(S.Context.IntTy), false);
      ArgSize = IntArg->getNumBits();

      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP, ArgSize,
                                           S.Context.IntTy, true, Info,
                                           Deduced);
    }

    if (const auto *IntArg = dyn_cast<DependentExtIntType>(Arg)) {
      if (IntParam->isUnsigned() != IntArg->isUnsigned())
        return Sema::TDK_NonDeducedMismatch;
      return Sema::TDK_Success;
    }
    return Sema::TDK_NonDeducedMismatch;
  }

  case Type::TypeOfExpr:
  case Type::TypeOf:
  case Type::DependentName:
  case Type::UnresolvedUsing:
  case Type::Decltype:
  case Type::UnaryTransform:
  case Type::Auto:
  case Type::DeducedTemplateSpecialization:
  case Type::DependentTemplateSpecialization:
  case Type::PackExpansion:
  case Type::Pipe:
    // No template argument deduction for these types
    return Sema::TDK_Success;
}

llvm_unreachable("Invalid Type Class!")__builtin_unreachable();
2306}

2308static Sema::TemplateDeductionResult
2309DeduceTemplateArguments(Sema &S,
                      TemplateParameterList *TemplateParams,
                      const TemplateArgument &Param,
                      TemplateArgument Arg,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
// If the template argument is a pack expansion, perform template argument
// deduction against the pattern of that expansion. This only occurs during
// partial ordering.
if (Arg.isPackExpansion())
  Arg = Arg.getPackExpansionPattern();

switch (Param.getKind()) {
case TemplateArgument::Null:
  llvm_unreachable("Null template argument in parameter list")__builtin_unreachable();

case TemplateArgument::Type:
  if (Arg.getKind() == TemplateArgument::Type)
    return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                              Param.getAsType(),
                                              Arg.getAsType(),
                                              Info, Deduced, 0);
  Info.FirstArg = Param;
  Info.SecondArg = Arg;
  return Sema::TDK_NonDeducedMismatch;

case TemplateArgument::Template:
  if (Arg.getKind() == TemplateArgument::Template)
    return DeduceTemplateArguments(S, TemplateParams,
                                   Param.getAsTemplate(),
                                   Arg.getAsTemplate(), Info, Deduced);
  Info.FirstArg = Param;
  Info.SecondArg = Arg;
  return Sema::TDK_NonDeducedMismatch;

case TemplateArgument::TemplateExpansion:
  llvm_unreachable("caller should handle pack expansions")__builtin_unreachable();

case TemplateArgument::Declaration:
  if (Arg.getKind() == TemplateArgument::Declaration &&
      isSameDeclaration(Param.getAsDecl(), Arg.getAsDecl()))
    return Sema::TDK_Success;

  Info.FirstArg = Param;
  Info.SecondArg = Arg;
  return Sema::TDK_NonDeducedMismatch;

case TemplateArgument::NullPtr:
  if (Arg.getKind() == TemplateArgument::NullPtr &&
      S.Context.hasSameType(Param.getNullPtrType(), Arg.getNullPtrType()))
    return Sema::TDK_Success;

  Info.FirstArg = Param;
  Info.SecondArg = Arg;
  return Sema::TDK_NonDeducedMismatch;

case TemplateArgument::Integral:
  if (Arg.getKind() == TemplateArgument::Integral) {
    if (hasSameExtendedValue(Param.getAsIntegral(), Arg.getAsIntegral()))
      return Sema::TDK_Success;

    Info.FirstArg = Param;
    Info.SecondArg = Arg;
    return Sema::TDK_NonDeducedMismatch;
  }

  if (Arg.getKind() == TemplateArgument::Expression) {
    Info.FirstArg = Param;
    Info.SecondArg = Arg;
    return Sema::TDK_NonDeducedMismatch;
  }

  Info.FirstArg = Param;
  Info.SecondArg = Arg;
  return Sema::TDK_NonDeducedMismatch;

case TemplateArgument::Expression:
  if (const NonTypeTemplateParmDecl *NTTP =
          getDeducedParameterFromExpr(Info, Param.getAsExpr())) {
    if (Arg.getKind() == TemplateArgument::Integral)
      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                           Arg.getAsIntegral(),
                                           Arg.getIntegralType(),
                                           /*ArrayBound=*/false,
                                           Info, Deduced);
    if (Arg.getKind() == TemplateArgument::NullPtr)
      return DeduceNullPtrTemplateArgument(S, TemplateParams, NTTP,
                                           Arg.getNullPtrType(),
                                           Info, Deduced);
    if (Arg.getKind() == TemplateArgument::Expression)
      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                           Arg.getAsExpr(), Info, Deduced);
    if (Arg.getKind() == TemplateArgument::Declaration)
      return DeduceNonTypeTemplateArgument(S, TemplateParams, NTTP,
                                           Arg.getAsDecl(),
                                           Arg.getParamTypeForDecl(),
                                           Info, Deduced);

    Info.FirstArg = Param;
    Info.SecondArg = Arg;
    return Sema::TDK_NonDeducedMismatch;
  }

  // Can't deduce anything, but that's okay.
  return Sema::TDK_Success;

case TemplateArgument::Pack:
  llvm_unreachable("Argument packs should be expanded by the caller!")__builtin_unreachable();
}

llvm_unreachable("Invalid TemplateArgument Kind!")__builtin_unreachable();
2420}

2422/// Determine whether there is a template argument to be used for
2423/// deduction.
2424///
2425/// This routine "expands" argument packs in-place, overriding its input
2426/// parameters so that \c Args[ArgIdx] will be the available template argument.
2427///
2428/// \returns true if there is another template argument (which will be at
2429/// \c Args[ArgIdx]), false otherwise.
2430static bool hasTemplateArgumentForDeduction(ArrayRef<TemplateArgument> &Args,
                                          unsigned &ArgIdx) {
if (ArgIdx == Args.size())
  return false;

const TemplateArgument &Arg = Args[ArgIdx];
if (Arg.getKind() != TemplateArgument::Pack)
  return true;

assert(ArgIdx == Args.size() - 1 && "Pack not at the end of argument list?")((void)0);
Args = Arg.pack_elements();
ArgIdx = 0;
return ArgIdx < Args.size();
2443}

2445/// Determine whether the given set of template arguments has a pack
2446/// expansion that is not the last template argument.
2447static bool hasPackExpansionBeforeEnd(ArrayRef<TemplateArgument> Args) {
bool FoundPackExpansion = false;
for (const auto &A : Args) {
  if (FoundPackExpansion)
    return true;

  if (A.getKind() == TemplateArgument::Pack)
    return hasPackExpansionBeforeEnd(A.pack_elements());

  // FIXME: If this is a fixed-arity pack expansion from an outer level of
  // templates, it should not be treated as a pack expansion.
  if (A.isPackExpansion())
    FoundPackExpansion = true;
}

return false;
2463}

2465static Sema::TemplateDeductionResult
2466DeduceTemplateArguments(Sema &S, TemplateParameterList *TemplateParams,
                      ArrayRef<TemplateArgument> Params,
                      ArrayRef<TemplateArgument> Args,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                      bool NumberOfArgumentsMustMatch) {
// C++0x [temp.deduct.type]p9:
//   If the template argument list of P contains a pack expansion that is not
//   the last template argument, the entire template argument list is a
//   non-deduced context.
if (hasPackExpansionBeforeEnd(Params))
  return Sema::TDK_Success;

// C++0x [temp.deduct.type]p9:
//   If P has a form that contains <T> or <i>, then each argument Pi of the
//   respective template argument list P is compared with the corresponding
//   argument Ai of the corresponding template argument list of A.
unsigned ArgIdx = 0, ParamIdx = 0;
for (; hasTemplateArgumentForDeduction(Params, ParamIdx); ++ParamIdx) {
  if (!Params[ParamIdx].isPackExpansion()) {
    // The simple case: deduce template arguments by matching Pi and Ai.

    // Check whether we have enough arguments.
    if (!hasTemplateArgumentForDeduction(Args, ArgIdx))
      return NumberOfArgumentsMustMatch
                 ? Sema::TDK_MiscellaneousDeductionFailure
                 : Sema::TDK_Success;

    // C++1z [temp.deduct.type]p9:
    //   During partial ordering, if Ai was originally a pack expansion [and]
    //   Pi is not a pack expansion, template argument deduction fails.
    if (Args[ArgIdx].isPackExpansion())
      return Sema::TDK_MiscellaneousDeductionFailure;

    // Perform deduction for this Pi/Ai pair.
    if (Sema::TemplateDeductionResult Result
          = DeduceTemplateArguments(S, TemplateParams,
                                    Params[ParamIdx], Args[ArgIdx],
                                    Info, Deduced))
      return Result;

    // Move to the next argument.
    ++ArgIdx;
    continue;
  }

  // The parameter is a pack expansion.

  // C++0x [temp.deduct.type]p9:
  //   If Pi is a pack expansion, then the pattern of Pi is compared with
  //   each remaining argument in the template argument list of A. Each
  //   comparison deduces template arguments for subsequent positions in the
  //   template parameter packs expanded by Pi.
  TemplateArgument Pattern = Params[ParamIdx].getPackExpansionPattern();

  // Prepare to deduce the packs within the pattern.
  PackDeductionScope PackScope(S, TemplateParams, Deduced, Info, Pattern);

  // Keep track of the deduced template arguments for each parameter pack
  // expanded by this pack expansion (the outer index) and for each
  // template argument (the inner SmallVectors).
  for (; hasTemplateArgumentForDeduction(Args, ArgIdx) &&
         PackScope.hasNextElement();
       ++ArgIdx) {
    // Deduce template arguments from the pattern.
    if (Sema::TemplateDeductionResult Result
          = DeduceTemplateArguments(S, TemplateParams, Pattern, Args[ArgIdx],
                                    Info, Deduced))
      return Result;

    PackScope.nextPackElement();
  }

  // Build argument packs for each of the parameter packs expanded by this
  // pack expansion.
  if (auto Result = PackScope.finish())
    return Result;
}

return Sema::TDK_Success;
2546}

2548static Sema::TemplateDeductionResult
2549DeduceTemplateArguments(Sema &S,
                      TemplateParameterList *TemplateParams,
                      const TemplateArgumentList &ParamList,
                      const TemplateArgumentList &ArgList,
                      TemplateDeductionInfo &Info,
                      SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
return DeduceTemplateArguments(S, TemplateParams, ParamList.asArray(),
                               ArgList.asArray(), Info, Deduced,
                               /*NumberOfArgumentsMustMatch*/false);
2558}

2560/// Determine whether two template arguments are the same.
2561static bool isSameTemplateArg(ASTContext &Context,
                            TemplateArgument X,
                            const TemplateArgument &Y,
                            bool PackExpansionMatchesPack = false) {
// If we're checking deduced arguments (X) against original arguments (Y),
// we will have flattened packs to non-expansions in X.
if (PackExpansionMatchesPack && X.isPackExpansion() && !Y.isPackExpansion())
  X = X.getPackExpansionPattern();

if (X.getKind() != Y.getKind())
  return false;

switch (X.getKind()) {
  case TemplateArgument::Null:
    llvm_unreachable("Comparing NULL template argument")__builtin_unreachable();

  case TemplateArgument::Type:
    return Context.getCanonicalType(X.getAsType()) ==
           Context.getCanonicalType(Y.getAsType());

  case TemplateArgument::Declaration:
    return isSameDeclaration(X.getAsDecl(), Y.getAsDecl());

  case TemplateArgument::NullPtr:
    return Context.hasSameType(X.getNullPtrType(), Y.getNullPtrType());

  case TemplateArgument::Template:
  case TemplateArgument::TemplateExpansion:
    return Context.getCanonicalTemplateName(
                  X.getAsTemplateOrTemplatePattern()).getAsVoidPointer() ==
           Context.getCanonicalTemplateName(
                  Y.getAsTemplateOrTemplatePattern()).getAsVoidPointer();

  case TemplateArgument::Integral:
    return hasSameExtendedValue(X.getAsIntegral(), Y.getAsIntegral());

  case TemplateArgument::Expression: {
    llvm::FoldingSetNodeID XID, YID;
    X.getAsExpr()->Profile(XID, Context, true);
    Y.getAsExpr()->Profile(YID, Context, true);
    return XID == YID;
  }

  case TemplateArgument::Pack:
    if (X.pack_size() != Y.pack_size())
      return false;

    for (TemplateArgument::pack_iterator XP = X.pack_begin(),
                                      XPEnd = X.pack_end(),
                                         YP = Y.pack_begin();
         XP != XPEnd; ++XP, ++YP)
      if (!isSameTemplateArg(Context, *XP, *YP, PackExpansionMatchesPack))
        return false;

    return true;
}

llvm_unreachable("Invalid TemplateArgument Kind!")__builtin_unreachable();
2619}

2621/// Allocate a TemplateArgumentLoc where all locations have
2622/// been initialized to the given location.
2623///
2624/// \param Arg The template argument we are producing template argument
2625/// location information for.
2626///
2627/// \param NTTPType For a declaration template argument, the type of
2628/// the non-type template parameter that corresponds to this template
2629/// argument. Can be null if no type sugar is available to add to the
2630/// type from the template argument.
2631///
2632/// \param Loc The source location to use for the resulting template
2633/// argument.
2634TemplateArgumentLoc
2635Sema::getTrivialTemplateArgumentLoc(const TemplateArgument &Arg,
                                  QualType NTTPType, SourceLocation Loc) {
switch (Arg.getKind()) {
case TemplateArgument::Null:
  llvm_unreachable("Can't get a NULL template argument here")__builtin_unreachable();

case TemplateArgument::Type:
  return TemplateArgumentLoc(
      Arg, Context.getTrivialTypeSourceInfo(Arg.getAsType(), Loc));

case TemplateArgument::Declaration: {
  if (NTTPType.isNull())
    NTTPType = Arg.getParamTypeForDecl();
  Expr *E = BuildExpressionFromDeclTemplateArgument(Arg, NTTPType, Loc)
                .getAs<Expr>();
  return TemplateArgumentLoc(TemplateArgument(E), E);
}

case TemplateArgument::NullPtr: {
  if (NTTPType.isNull())
    NTTPType = Arg.getNullPtrType();
  Expr *E = BuildExpressionFromDeclTemplateArgument(Arg, NTTPType, Loc)
                .getAs<Expr>();
  return TemplateArgumentLoc(TemplateArgument(NTTPType, /*isNullPtr*/true),
                             E);
}

case TemplateArgument::Integral: {
  Expr *E =
      BuildExpressionFromIntegralTemplateArgument(Arg, Loc).getAs<Expr>();
  return TemplateArgumentLoc(TemplateArgument(E), E);
}

  case TemplateArgument::Template:
  case TemplateArgument::TemplateExpansion: {
    NestedNameSpecifierLocBuilder Builder;
    TemplateName Template = Arg.getAsTemplateOrTemplatePattern();
    if (DependentTemplateName *DTN = Template.getAsDependentTemplateName())
      Builder.MakeTrivial(Context, DTN->getQualifier(), Loc);
    else if (QualifiedTemplateName *QTN =
                 Template.getAsQualifiedTemplateName())
      Builder.MakeTrivial(Context, QTN->getQualifier(), Loc);

    if (Arg.getKind() == TemplateArgument::Template)
      return TemplateArgumentLoc(Context, Arg,
                                 Builder.getWithLocInContext(Context), Loc);

    return TemplateArgumentLoc(
        Context, Arg, Builder.getWithLocInContext(Context), Loc, Loc);
  }

case TemplateArgument::Expression:
  return TemplateArgumentLoc(Arg, Arg.getAsExpr());

case TemplateArgument::Pack:
  return TemplateArgumentLoc(Arg, TemplateArgumentLocInfo());
}

llvm_unreachable("Invalid TemplateArgument Kind!")__builtin_unreachable();
2694}

2696TemplateArgumentLoc
2697Sema::getIdentityTemplateArgumentLoc(NamedDecl *TemplateParm,
                                   SourceLocation Location) {
return getTrivialTemplateArgumentLoc(
    Context.getInjectedTemplateArg(TemplateParm), QualType(), Location);
2701}

2703/// Convert the given deduced template argument and add it to the set of
2704/// fully-converted template arguments.
2705static bool
2706ConvertDeducedTemplateArgument(Sema &S, NamedDecl *Param,
                             DeducedTemplateArgument Arg,
                             NamedDecl *Template,
                             TemplateDeductionInfo &Info,
                             bool IsDeduced,
                             SmallVectorImpl<TemplateArgument> &Output) {
auto ConvertArg = [&](DeducedTemplateArgument Arg,
                      unsigned ArgumentPackIndex) {
  // Convert the deduced template argument into a template
  // argument that we can check, almost as if the user had written
  // the template argument explicitly.
  TemplateArgumentLoc ArgLoc =
      S.getTrivialTemplateArgumentLoc(Arg, QualType(), Info.getLocation());

  // Check the template argument, converting it as necessary.
  return S.CheckTemplateArgument(
      Param, ArgLoc, Template, Template->getLocation(),
      Template->getSourceRange().getEnd(), ArgumentPackIndex, Output,
      IsDeduced
          ? (Arg.wasDeducedFromArrayBound() ? Sema::CTAK_DeducedFromArrayBound
                                            : Sema::CTAK_Deduced)
          : Sema::CTAK_Specified);
};

if (Arg.getKind() == TemplateArgument::Pack) {
  // This is a template argument pack, so check each of its arguments against
  // the template parameter.
  SmallVector<TemplateArgument, 2> PackedArgsBuilder;
  for (const auto &P : Arg.pack_elements()) {
    // When converting the deduced template argument, append it to the
    // general output list. We need to do this so that the template argument
    // checking logic has all of the prior template arguments available.
    DeducedTemplateArgument InnerArg(P);
    InnerArg.setDeducedFromArrayBound(Arg.wasDeducedFromArrayBound());
    assert(InnerArg.getKind() != TemplateArgument::Pack &&((void)0)
           "deduced nested pack")((void)0);
    if (P.isNull()) {
      // We deduced arguments for some elements of this pack, but not for
      // all of them. This happens if we get a conditionally-non-deduced
      // context in a pack expansion (such as an overload set in one of the
      // arguments).
      S.Diag(Param->getLocation(),
             diag::err_template_arg_deduced_incomplete_pack)
        << Arg << Param;
      return true;
    }
    if (ConvertArg(InnerArg, PackedArgsBuilder.size()))
      return true;

    // Move the converted template argument into our argument pack.
    PackedArgsBuilder.push_back(Output.pop_back_val());
  }

  // If the pack is empty, we still need to substitute into the parameter
  // itself, in case that substitution fails.
  if (PackedArgsBuilder.empty()) {
    LocalInstantiationScope Scope(S);
    TemplateArgumentList TemplateArgs(TemplateArgumentList::OnStack, Output);
    MultiLevelTemplateArgumentList Args(TemplateArgs);

    if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(Param)) {
      Sema::InstantiatingTemplate Inst(S, Template->getLocation(), Template,
                                       NTTP, Output,
                                       Template->getSourceRange());
      if (Inst.isInvalid() ||
          S.SubstType(NTTP->getType(), Args, NTTP->getLocation(),
                      NTTP->getDeclName()).isNull())
        return true;
    } else if (auto *TTP = dyn_cast<TemplateTemplateParmDecl>(Param)) {
      Sema::InstantiatingTemplate Inst(S, Template->getLocation(), Template,
                                       TTP, Output,
                                       Template->getSourceRange());
      if (Inst.isInvalid() || !S.SubstDecl(TTP, S.CurContext, Args))
        return true;
    }
    // For type parameters, no substitution is ever required.
  }

  // Create the resulting argument pack.
  Output.push_back(
      TemplateArgument::CreatePackCopy(S.Context, PackedArgsBuilder));
  return false;
}

return ConvertArg(Arg, 0);
2791}

2793// FIXME: This should not be a template, but
2794// ClassTemplatePartialSpecializationDecl sadly does not derive from
2795// TemplateDecl.
2796template<typename TemplateDeclT>
2797static Sema::TemplateDeductionResult ConvertDeducedTemplateArguments(
  Sema &S, TemplateDeclT *Template, bool IsDeduced,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  TemplateDeductionInfo &Info, SmallVectorImpl<TemplateArgument> &Builder,
  LocalInstantiationScope *CurrentInstantiationScope = nullptr,
  unsigned NumAlreadyConverted = 0, bool PartialOverloading = false) {
TemplateParameterList *TemplateParams = Template->getTemplateParameters();

for (unsigned I = 0, N = TemplateParams->size(); I != N; ++I) {
  NamedDecl *Param = TemplateParams->getParam(I);

  // C++0x [temp.arg.explicit]p3:
  //    A trailing template parameter pack (14.5.3) not otherwise deduced will
  //    be deduced to an empty sequence of template arguments.
  // FIXME: Where did the word "trailing" come from?
  if (Deduced[I].isNull() && Param->isTemplateParameterPack()) {
    if (auto Result =
            PackDeductionScope(S, TemplateParams, Deduced, Info, I).finish())
      return Result;
  }

  if (!Deduced[I].isNull()) {
    if (I < NumAlreadyConverted) {
      // We may have had explicitly-specified template arguments for a
      // template parameter pack (that may or may not have been extended
      // via additional deduced arguments).
      if (Param->isParameterPack() && CurrentInstantiationScope &&
          CurrentInstantiationScope->getPartiallySubstitutedPack() == Param) {
        // Forget the partially-substituted pack; its substitution is now
        // complete.
        CurrentInstantiationScope->ResetPartiallySubstitutedPack();
        // We still need to check the argument in case it was extended by
        // deduction.
      } else {
        // We have already fully type-checked and converted this
        // argument, because it was explicitly-specified. Just record the
        // presence of this argument.
        Builder.push_back(Deduced[I]);
        continue;
      }
    }

    // We may have deduced this argument, so it still needs to be
    // checked and converted.
    if (ConvertDeducedTemplateArgument(S, Param, Deduced[I], Template, Info,
                                       IsDeduced, Builder)) {
      Info.Param = makeTemplateParameter(Param);
      // FIXME: These template arguments are temporary. Free them!
      Info.reset(TemplateArgumentList::CreateCopy(S.Context, Builder));
      return Sema::TDK_SubstitutionFailure;
    }

    continue;
  }

  // Substitute into the default template argument, if available.
  bool HasDefaultArg = false;
  TemplateDecl *TD = dyn_cast<TemplateDecl>(Template);
  if (!TD) {
    assert(isa<ClassTemplatePartialSpecializationDecl>(Template) ||((void)0)
           isa<VarTemplatePartialSpecializationDecl>(Template))((void)0);
    return Sema::TDK_Incomplete;
  }

  TemplateArgumentLoc DefArg = S.SubstDefaultTemplateArgumentIfAvailable(
      TD, TD->getLocation(), TD->getSourceRange().getEnd(), Param, Builder,
      HasDefaultArg);

  // If there was no default argument, deduction is incomplete.
  if (DefArg.getArgument().isNull()) {
    Info.Param = makeTemplateParameter(
        const_cast<NamedDecl *>(TemplateParams->getParam(I)));
    Info.reset(TemplateArgumentList::CreateCopy(S.Context, Builder));
    if (PartialOverloading) break;

    return HasDefaultArg ? Sema::TDK_SubstitutionFailure
                         : Sema::TDK_Incomplete;
  }

  // Check whether we can actually use the default argument.
  if (S.CheckTemplateArgument(Param, DefArg, TD, TD->getLocation(),
                              TD->getSourceRange().getEnd(), 0, Builder,
                              Sema::CTAK_Specified)) {
    Info.Param = makeTemplateParameter(
                       const_cast<NamedDecl *>(TemplateParams->getParam(I)));
    // FIXME: These template arguments are temporary. Free them!
    Info.reset(TemplateArgumentList::CreateCopy(S.Context, Builder));
    return Sema::TDK_SubstitutionFailure;
  }

  // If we get here, we successfully used the default template argument.
}

return Sema::TDK_Success;
2891}

2893static DeclContext *getAsDeclContextOrEnclosing(Decl *D) {
if (auto *DC = dyn_cast<DeclContext>(D))
  return DC;
return D->getDeclContext();
2897}

2899template<typename T> struct IsPartialSpecialization {
static constexpr bool value = false;
2901};
2902template<>
2903struct IsPartialSpecialization<ClassTemplatePartialSpecializationDecl> {
static constexpr bool value = true;
2905};
2906template<>
2907struct IsPartialSpecialization<VarTemplatePartialSpecializationDecl> {
static constexpr bool value = true;
2909};

2911template<typename TemplateDeclT>
2912static Sema::TemplateDeductionResult
2913CheckDeducedArgumentConstraints(Sema& S, TemplateDeclT *Template,
                              ArrayRef<TemplateArgument> DeducedArgs,
                              TemplateDeductionInfo& Info) {
llvm::SmallVector<const Expr *, 3> AssociatedConstraints;
Template->getAssociatedConstraints(AssociatedConstraints);
if (S.CheckConstraintSatisfaction(Template, AssociatedConstraints,
                                  DeducedArgs, Info.getLocation(),
                                  Info.AssociatedConstraintsSatisfaction) ||
    !Info.AssociatedConstraintsSatisfaction.IsSatisfied) {
  Info.reset(TemplateArgumentList::CreateCopy(S.Context, DeducedArgs));
  return Sema::TDK_ConstraintsNotSatisfied;
}
return Sema::TDK_Success;
2926}

2928/// Complete template argument deduction for a partial specialization.
2929template <typename T>
2930static std::enable_if_t<IsPartialSpecialization<T>::value,
                      Sema::TemplateDeductionResult>
2932FinishTemplateArgumentDeduction(
  Sema &S, T *Partial, bool IsPartialOrdering,
  const TemplateArgumentList &TemplateArgs,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  TemplateDeductionInfo &Info) {
// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    S, Sema::ExpressionEvaluationContext::Unevaluated);
Sema::SFINAETrap Trap(S);

Sema::ContextRAII SavedContext(S, getAsDeclContextOrEnclosing(Partial));

// C++ [temp.deduct.type]p2:
//   [...] or if any template argument remains neither deduced nor
//   explicitly specified, template argument deduction fails.
SmallVector<TemplateArgument, 4> Builder;
if (auto Result = ConvertDeducedTemplateArguments(
        S, Partial, IsPartialOrdering, Deduced, Info, Builder))
  return Result;

// Form the template argument list from the deduced template arguments.
TemplateArgumentList *DeducedArgumentList
  = TemplateArgumentList::CreateCopy(S.Context, Builder);

Info.reset(DeducedArgumentList);

// Substitute the deduced template arguments into the template
// arguments of the class template partial specialization, and
// verify that the instantiated template arguments are both valid
// and are equivalent to the template arguments originally provided
// to the class template.
LocalInstantiationScope InstScope(S);
auto *Template = Partial->getSpecializedTemplate();
const ASTTemplateArgumentListInfo *PartialTemplArgInfo =
    Partial->getTemplateArgsAsWritten();
const TemplateArgumentLoc *PartialTemplateArgs =
    PartialTemplArgInfo->getTemplateArgs();

TemplateArgumentListInfo InstArgs(PartialTemplArgInfo->LAngleLoc,
                                  PartialTemplArgInfo->RAngleLoc);

if (S.Subst(PartialTemplateArgs, PartialTemplArgInfo->NumTemplateArgs,
            InstArgs, MultiLevelTemplateArgumentList(*DeducedArgumentList))) {
  unsigned ArgIdx = InstArgs.size(), ParamIdx = ArgIdx;
  if (ParamIdx >= Partial->getTemplateParameters()->size())
    ParamIdx = Partial->getTemplateParameters()->size() - 1;

  Decl *Param = const_cast<NamedDecl *>(
      Partial->getTemplateParameters()->getParam(ParamIdx));
  Info.Param = makeTemplateParameter(Param);
  Info.FirstArg = PartialTemplateArgs[ArgIdx].getArgument();
  return Sema::TDK_SubstitutionFailure;
}

bool ConstraintsNotSatisfied;
SmallVector<TemplateArgument, 4> ConvertedInstArgs;
if (S.CheckTemplateArgumentList(Template, Partial->getLocation(), InstArgs,
                                false, ConvertedInstArgs,
                                /*UpdateArgsWithConversions=*/true,
                                &ConstraintsNotSatisfied))
  return ConstraintsNotSatisfied ? Sema::TDK_ConstraintsNotSatisfied :
                                   Sema::TDK_SubstitutionFailure;

TemplateParameterList *TemplateParams = Template->getTemplateParameters();
for (unsigned I = 0, E = TemplateParams->size(); I != E; ++I) {
  TemplateArgument InstArg = ConvertedInstArgs.data()[I];
  if (!isSameTemplateArg(S.Context, TemplateArgs[I], InstArg)) {
    Info.Param = makeTemplateParameter(TemplateParams->getParam(I));
    Info.FirstArg = TemplateArgs[I];
    Info.SecondArg = InstArg;
    return Sema::TDK_NonDeducedMismatch;
  }
}

if (Trap.hasErrorOccurred())
  return Sema::TDK_SubstitutionFailure;

if (auto Result = CheckDeducedArgumentConstraints(S, Partial, Builder, Info))
  return Result;

return Sema::TDK_Success;
3013}

3015/// Complete template argument deduction for a class or variable template,
3016/// when partial ordering against a partial specialization.
3017// FIXME: Factor out duplication with partial specialization version above.
3018static Sema::TemplateDeductionResult FinishTemplateArgumentDeduction(
  Sema &S, TemplateDecl *Template, bool PartialOrdering,
  const TemplateArgumentList &TemplateArgs,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  TemplateDeductionInfo &Info) {
// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    S, Sema::ExpressionEvaluationContext::Unevaluated);
Sema::SFINAETrap Trap(S);

Sema::ContextRAII SavedContext(S, getAsDeclContextOrEnclosing(Template));

// C++ [temp.deduct.type]p2:
//   [...] or if any template argument remains neither deduced nor
//   explicitly specified, template argument deduction fails.
SmallVector<TemplateArgument, 4> Builder;
if (auto Result = ConvertDeducedTemplateArguments(
        S, Template, /*IsDeduced*/PartialOrdering, Deduced, Info, Builder))
  return Result;

// Check that we produced the correct argument list.
TemplateParameterList *TemplateParams = Template->getTemplateParameters();
for (unsigned I = 0, E = TemplateParams->size(); I != E; ++I) {
  TemplateArgument InstArg = Builder[I];
  if (!isSameTemplateArg(S.Context, TemplateArgs[I], InstArg,
                         /*PackExpansionMatchesPack*/true)) {
    Info.Param = makeTemplateParameter(TemplateParams->getParam(I));
    Info.FirstArg = TemplateArgs[I];
    Info.SecondArg = InstArg;
    return Sema::TDK_NonDeducedMismatch;
  }
}

if (Trap.hasErrorOccurred())
  return Sema::TDK_SubstitutionFailure;

if (auto Result = CheckDeducedArgumentConstraints(S, Template, Builder,
                                                  Info))
  return Result;

return Sema::TDK_Success;
3059}

3061/// Perform template argument deduction to determine whether
3062/// the given template arguments match the given class template
3063/// partial specialization per C++ [temp.class.spec.match].
3064Sema::TemplateDeductionResult
3065Sema::DeduceTemplateArguments(ClassTemplatePartialSpecializationDecl *Partial,
                            const TemplateArgumentList &TemplateArgs,
                            TemplateDeductionInfo &Info) {
if (Partial->isInvalidDecl())
  return TDK_Invalid;

// C++ [temp.class.spec.match]p2:
//   A partial specialization matches a given actual template
//   argument list if the template arguments of the partial
//   specialization can be deduced from the actual template argument
//   list (14.8.2).

// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    *this, Sema::ExpressionEvaluationContext::Unevaluated);
SFINAETrap Trap(*this);

// This deduction has no relation to any outer instantiation we might be
// performing.
LocalInstantiationScope InstantiationScope(*this);

SmallVector<DeducedTemplateArgument, 4> Deduced;
Deduced.resize(Partial->getTemplateParameters()->size());
if (TemplateDeductionResult Result
      = ::DeduceTemplateArguments(*this,
                                  Partial->getTemplateParameters(),
                                  Partial->getTemplateArgs(),
                                  TemplateArgs, Info, Deduced))
  return Result;

SmallVector<TemplateArgument, 4> DeducedArgs(Deduced.begin(), Deduced.end());
InstantiatingTemplate Inst(*this, Info.getLocation(), Partial, DeducedArgs,
                           Info);
if (Inst.isInvalid())
  return TDK_InstantiationDepth;

if (Trap.hasErrorOccurred())
  return Sema::TDK_SubstitutionFailure;

TemplateDeductionResult Result;
runWithSufficientStackSpace(Info.getLocation(), [&] {
  Result = ::FinishTemplateArgumentDeduction(*this, Partial,
                                             /*IsPartialOrdering=*/false,
                                             TemplateArgs, Deduced, Info);
});
return Result;
3111}

3113/// Perform template argument deduction to determine whether
3114/// the given template arguments match the given variable template
3115/// partial specialization per C++ [temp.class.spec.match].
3116Sema::TemplateDeductionResult
3117Sema::DeduceTemplateArguments(VarTemplatePartialSpecializationDecl *Partial,
                            const TemplateArgumentList &TemplateArgs,
                            TemplateDeductionInfo &Info) {
if (Partial->isInvalidDecl())
  return TDK_Invalid;

// C++ [temp.class.spec.match]p2:
//   A partial specialization matches a given actual template
//   argument list if the template arguments of the partial
//   specialization can be deduced from the actual template argument
//   list (14.8.2).

// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    *this, Sema::ExpressionEvaluationContext::Unevaluated);
SFINAETrap Trap(*this);

// This deduction has no relation to any outer instantiation we might be
// performing.
LocalInstantiationScope InstantiationScope(*this);

SmallVector<DeducedTemplateArgument, 4> Deduced;
Deduced.resize(Partial->getTemplateParameters()->size());
if (TemplateDeductionResult Result = ::DeduceTemplateArguments(
        *this, Partial->getTemplateParameters(), Partial->getTemplateArgs(),
        TemplateArgs, Info, Deduced))
  return Result;

SmallVector<TemplateArgument, 4> DeducedArgs(Deduced.begin(), Deduced.end());
InstantiatingTemplate Inst(*this, Info.getLocation(), Partial, DeducedArgs,
                           Info);
if (Inst.isInvalid())
  return TDK_InstantiationDepth;

if (Trap.hasErrorOccurred())
  return Sema::TDK_SubstitutionFailure;

TemplateDeductionResult Result;
runWithSufficientStackSpace(Info.getLocation(), [&] {
  Result = ::FinishTemplateArgumentDeduction(*this, Partial,
                                             /*IsPartialOrdering=*/false,
                                             TemplateArgs, Deduced, Info);
});
return Result;
3161}

3163/// Determine whether the given type T is a simple-template-id type.
3164static bool isSimpleTemplateIdType(QualType T) {
if (const TemplateSpecializationType *Spec
      = T->getAs<TemplateSpecializationType>())
  return Spec->getTemplateName().getAsTemplateDecl() != nullptr;

// C++17 [temp.local]p2:
//   the injected-class-name [...] is equivalent to the template-name followed
//   by the template-arguments of the class template specialization or partial
//   specialization enclosed in <>
// ... which means it's equivalent to a simple-template-id.
//
// This only arises during class template argument deduction for a copy
// deduction candidate, where it permits slicing.
if (T->getAs<InjectedClassNameType>())
  return true;

return false;
3181}

3183/// Substitute the explicitly-provided template arguments into the
3184/// given function template according to C++ [temp.arg.explicit].
3185///
3186/// \param FunctionTemplate the function template into which the explicit
3187/// template arguments will be substituted.
3188///
3189/// \param ExplicitTemplateArgs the explicitly-specified template
3190/// arguments.
3191///
3192/// \param Deduced the deduced template arguments, which will be populated
3193/// with the converted and checked explicit template arguments.
3194///
3195/// \param ParamTypes will be populated with the instantiated function
3196/// parameters.
3197///
3198/// \param FunctionType if non-NULL, the result type of the function template
3199/// will also be instantiated and the pointed-to value will be updated with
3200/// the instantiated function type.
3201///
3202/// \param Info if substitution fails for any reason, this object will be
3203/// populated with more information about the failure.
3204///
3205/// \returns TDK_Success if substitution was successful, or some failure
3206/// condition.
3207Sema::TemplateDeductionResult
3208Sema::SubstituteExplicitTemplateArguments(
                                    FunctionTemplateDecl *FunctionTemplate,
                             TemplateArgumentListInfo &ExplicitTemplateArgs,
                     SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                               SmallVectorImpl<QualType> &ParamTypes,
                                        QualType *FunctionType,
                                        TemplateDeductionInfo &Info) {
FunctionDecl *Function = FunctionTemplate->getTemplatedDecl();
TemplateParameterList *TemplateParams
  = FunctionTemplate->getTemplateParameters();

if (ExplicitTemplateArgs.size() == 0) {
2
←
Assuming the condition is false→
3
←
Taking false branch→
  // No arguments to substitute; just copy over the parameter types and
  // fill in the function type.
  for (auto P : Function->parameters())
    ParamTypes.push_back(P->getType());

  if (FunctionType)
    *FunctionType = Function->getType();
  return TDK_Success;
}

// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    *this, Sema::ExpressionEvaluationContext::Unevaluated);
SFINAETrap Trap(*this);

// C++ [temp.arg.explicit]p3:
//   Template arguments that are present shall be specified in the
//   declaration order of their corresponding template-parameters. The
//   template argument list shall not specify more template-arguments than
//   there are corresponding template-parameters.
SmallVector<TemplateArgument, 4> Builder;

// Enter a new template instantiation context where we check the
// explicitly-specified template arguments against this function template,
// and then substitute them into the function parameter types.
SmallVector<TemplateArgument, 4> DeducedArgs;
InstantiatingTemplate Inst(
    *this, Info.getLocation(), FunctionTemplate, DeducedArgs,
    CodeSynthesisContext::ExplicitTemplateArgumentSubstitution, Info);
if (Inst.isInvalid())
4
←
Assuming the condition is false→
5
←
Taking false branch→
  return TDK_InstantiationDepth;

if (CheckTemplateArgumentList(FunctionTemplate, SourceLocation(),
6
←
Assuming the condition is false→
7
←
Taking false branch→
                              ExplicitTemplateArgs, true, Builder, false) ||
    Trap.hasErrorOccurred()) {
  unsigned Index = Builder.size();
  if (Index >= TemplateParams->size())
    return TDK_SubstitutionFailure;
  Info.Param = makeTemplateParameter(TemplateParams->getParam(Index));
  return TDK_InvalidExplicitArguments;
}

// Form the template argument list from the explicitly-specified
// template arguments.
TemplateArgumentList *ExplicitArgumentList
  = TemplateArgumentList::CreateCopy(Context, Builder);
Info.setExplicitArgs(ExplicitArgumentList);

// Template argument deduction and the final substitution should be
// done in the context of the templated declaration.  Explicit
// argument substitution, on the other hand, needs to happen in the
// calling context.
ContextRAII SavedContext(*this, FunctionTemplate->getTemplatedDecl());

// If we deduced template arguments for a template parameter pack,
// note that the template argument pack is partially substituted and record
// the explicit template arguments. They'll be used as part of deduction
// for this template parameter pack.
unsigned PartiallySubstitutedPackIndex = -1u;
if (!Builder.empty()) {
8
←
Taking false branch→
  const TemplateArgument &Arg = Builder.back();
  if (Arg.getKind() == TemplateArgument::Pack) {
    auto *Param = TemplateParams->getParam(Builder.size() - 1);
    // If this is a fully-saturated fixed-size pack, it should be
    // fully-substituted, not partially-substituted.
    Optional<unsigned> Expansions = getExpandedPackSize(Param);
    if (!Expansions || Arg.pack_size() < *Expansions) {
      PartiallySubstitutedPackIndex = Builder.size() - 1;
      CurrentInstantiationScope->SetPartiallySubstitutedPack(
          Param, Arg.pack_begin(), Arg.pack_size());
    }
  }
}

const FunctionProtoType *Proto
10
←
'Proto' initialized to a null pointer value→
  = Function->getType()->getAs<FunctionProtoType>();
9
←
Assuming the object is not a 'FunctionProtoType'→
assert(Proto && "Function template does not have a prototype?")((void)0);

// Isolate our substituted parameters from our caller.
LocalInstantiationScope InstScope(*this, /*MergeWithOuterScope*/true);

ExtParameterInfoBuilder ExtParamInfos;

// Instantiate the types of each of the function parameters given the
// explicitly-specified template arguments. If the function has a trailing
// return type, substitute it after the arguments to ensure we substitute
// in lexical order.
if (Proto->hasTrailingReturn()) {
11
←
Called C++ object pointer is null
  if (SubstParmTypes(Function->getLocation(), Function->parameters(),
                     Proto->getExtParameterInfosOrNull(),
                     MultiLevelTemplateArgumentList(*ExplicitArgumentList),
                     ParamTypes, /*params*/ nullptr, ExtParamInfos))
    return TDK_SubstitutionFailure;
}

// Instantiate the return type.
QualType ResultType;
{
  // C++11 [expr.prim.general]p3:
  //   If a declaration declares a member function or member function
  //   template of a class X, the expression this is a prvalue of type
  //   "pointer to cv-qualifier-seq X" between the optional cv-qualifer-seq
  //   and the end of the function-definition, member-declarator, or
  //   declarator.
  Qualifiers ThisTypeQuals;
  CXXRecordDecl *ThisContext = nullptr;
  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Function)) {
    ThisContext = Method->getParent();
    ThisTypeQuals = Method->getMethodQualifiers();
  }

  CXXThisScopeRAII ThisScope(*this, ThisContext, ThisTypeQuals,
                             getLangOpts().CPlusPlus11);

  ResultType =
      SubstType(Proto->getReturnType(),
                MultiLevelTemplateArgumentList(*ExplicitArgumentList),
                Function->getTypeSpecStartLoc(), Function->getDeclName());
  if (ResultType.isNull() || Trap.hasErrorOccurred())
    return TDK_SubstitutionFailure;
  // CUDA: Kernel function must have 'void' return type.
  if (getLangOpts().CUDA)
    if (Function->hasAttr<CUDAGlobalAttr>() && !ResultType->isVoidType()) {
      Diag(Function->getLocation(), diag::err_kern_type_not_void_return)
          << Function->getType() << Function->getSourceRange();
      return TDK_SubstitutionFailure;
    }
}

// Instantiate the types of each of the function parameters given the
// explicitly-specified template arguments if we didn't do so earlier.
if (!Proto->hasTrailingReturn() &&
    SubstParmTypes(Function->getLocation(), Function->parameters(),
                   Proto->getExtParameterInfosOrNull(),
                   MultiLevelTemplateArgumentList(*ExplicitArgumentList),
                   ParamTypes, /*params*/ nullptr, ExtParamInfos))
  return TDK_SubstitutionFailure;

if (FunctionType) {
  auto EPI = Proto->getExtProtoInfo();
  EPI.ExtParameterInfos = ExtParamInfos.getPointerOrNull(ParamTypes.size());

  // In C++1z onwards, exception specifications are part of the function type,
  // so substitution into the type must also substitute into the exception
  // specification.
  SmallVector<QualType, 4> ExceptionStorage;
  if (getLangOpts().CPlusPlus17 &&
      SubstExceptionSpec(
          Function->getLocation(), EPI.ExceptionSpec, ExceptionStorage,
          MultiLevelTemplateArgumentList(*ExplicitArgumentList)))
    return TDK_SubstitutionFailure;

  *FunctionType = BuildFunctionType(ResultType, ParamTypes,
                                    Function->getLocation(),
                                    Function->getDeclName(),
                                    EPI);
  if (FunctionType->isNull() || Trap.hasErrorOccurred())
    return TDK_SubstitutionFailure;
}

// C++ [temp.arg.explicit]p2:
//   Trailing template arguments that can be deduced (14.8.2) may be
//   omitted from the list of explicit template-arguments. If all of the
//   template arguments can be deduced, they may all be omitted; in this
//   case, the empty template argument list <> itself may also be omitted.
//
// Take all of the explicitly-specified arguments and put them into
// the set of deduced template arguments. The partially-substituted
// parameter pack, however, will be set to NULL since the deduction
// mechanism handles the partially-substituted argument pack directly.
Deduced.reserve(TemplateParams->size());
for (unsigned I = 0, N = ExplicitArgumentList->size(); I != N; ++I) {
  const TemplateArgument &Arg = ExplicitArgumentList->get(I);
  if (I == PartiallySubstitutedPackIndex)
    Deduced.push_back(DeducedTemplateArgument());
  else
    Deduced.push_back(Arg);
}

return TDK_Success;
3400}

3402/// Check whether the deduced argument type for a call to a function
3403/// template matches the actual argument type per C++ [temp.deduct.call]p4.
3404static Sema::TemplateDeductionResult
3405CheckOriginalCallArgDeduction(Sema &S, TemplateDeductionInfo &Info,
                            Sema::OriginalCallArg OriginalArg,
                            QualType DeducedA) {
ASTContext &Context = S.Context;

auto Failed = [&]() -> Sema::TemplateDeductionResult {
  Info.FirstArg = TemplateArgument(DeducedA);
  Info.SecondArg = TemplateArgument(OriginalArg.OriginalArgType);
  Info.CallArgIndex = OriginalArg.ArgIdx;
  return OriginalArg.DecomposedParam ? Sema::TDK_DeducedMismatchNested
                                     : Sema::TDK_DeducedMismatch;
};

QualType A = OriginalArg.OriginalArgType;
QualType OriginalParamType = OriginalArg.OriginalParamType;

// Check for type equality (top-level cv-qualifiers are ignored).
if (Context.hasSameUnqualifiedType(A, DeducedA))
  return Sema::TDK_Success;

// Strip off references on the argument types; they aren't needed for
// the following checks.
if (const ReferenceType *DeducedARef = DeducedA->getAs<ReferenceType>())
  DeducedA = DeducedARef->getPointeeType();
if (const ReferenceType *ARef = A->getAs<ReferenceType>())
  A = ARef->getPointeeType();

// C++ [temp.deduct.call]p4:
//   [...] However, there are three cases that allow a difference:
//     - If the original P is a reference type, the deduced A (i.e., the
//       type referred to by the reference) can be more cv-qualified than
//       the transformed A.
if (const ReferenceType *OriginalParamRef
    = OriginalParamType->getAs<ReferenceType>()) {
  // We don't want to keep the reference around any more.
  OriginalParamType = OriginalParamRef->getPointeeType();

  // FIXME: Resolve core issue (no number yet): if the original P is a
  // reference type and the transformed A is function type "noexcept F",
  // the deduced A can be F.
  QualType Tmp;
  if (A->isFunctionType() && S.IsFunctionConversion(A, DeducedA, Tmp))
    return Sema::TDK_Success;

  Qualifiers AQuals = A.getQualifiers();
  Qualifiers DeducedAQuals = DeducedA.getQualifiers();

  // Under Objective-C++ ARC, the deduced type may have implicitly
  // been given strong or (when dealing with a const reference)
  // unsafe_unretained lifetime. If so, update the original
  // qualifiers to include this lifetime.
  if (S.getLangOpts().ObjCAutoRefCount &&
      ((DeducedAQuals.getObjCLifetime() == Qualifiers::OCL_Strong &&
        AQuals.getObjCLifetime() == Qualifiers::OCL_None) ||
       (DeducedAQuals.hasConst() &&
        DeducedAQuals.getObjCLifetime() == Qualifiers::OCL_ExplicitNone))) {
    AQuals.setObjCLifetime(DeducedAQuals.getObjCLifetime());
  }

  if (AQuals == DeducedAQuals) {
    // Qualifiers match; there's nothing to do.
  } else if (!DeducedAQuals.compatiblyIncludes(AQuals)) {
    return Failed();
  } else {
    // Qualifiers are compatible, so have the argument type adopt the
    // deduced argument type's qualifiers as if we had performed the
    // qualification conversion.
    A = Context.getQualifiedType(A.getUnqualifiedType(), DeducedAQuals);
  }
}

//    - The transformed A can be another pointer or pointer to member
//      type that can be converted to the deduced A via a function pointer
//      conversion and/or a qualification conversion.
//
// Also allow conversions which merely strip __attribute__((noreturn)) from
// function types (recursively).
bool ObjCLifetimeConversion = false;
QualType ResultTy;
if ((A->isAnyPointerType() || A->isMemberPointerType()) &&
    (S.IsQualificationConversion(A, DeducedA, false,
                                 ObjCLifetimeConversion) ||
     S.IsFunctionConversion(A, DeducedA, ResultTy)))
  return Sema::TDK_Success;

//    - If P is a class and P has the form simple-template-id, then the
//      transformed A can be a derived class of the deduced A. [...]
//     [...] Likewise, if P is a pointer to a class of the form
//      simple-template-id, the transformed A can be a pointer to a
//      derived class pointed to by the deduced A.
if (const PointerType *OriginalParamPtr
    = OriginalParamType->getAs<PointerType>()) {
  if (const PointerType *DeducedAPtr = DeducedA->getAs<PointerType>()) {
    if (const PointerType *APtr = A->getAs<PointerType>()) {
      if (A->getPointeeType()->isRecordType()) {
        OriginalParamType = OriginalParamPtr->getPointeeType();
        DeducedA = DeducedAPtr->getPointeeType();
        A = APtr->getPointeeType();
      }
    }
  }
}

if (Context.hasSameUnqualifiedType(A, DeducedA))
  return Sema::TDK_Success;

if (A->isRecordType() && isSimpleTemplateIdType(OriginalParamType) &&
    S.IsDerivedFrom(Info.getLocation(), A, DeducedA))
  return Sema::TDK_Success;

return Failed();
3516}

3518/// Find the pack index for a particular parameter index in an instantiation of
3519/// a function template with specific arguments.
3520///
3521/// \return The pack index for whichever pack produced this parameter, or -1
3522///         if this was not produced by a parameter. Intended to be used as the
3523///         ArgumentPackSubstitutionIndex for further substitutions.
3524// FIXME: We should track this in OriginalCallArgs so we don't need to
3525// reconstruct it here.
3526static unsigned getPackIndexForParam(Sema &S,
                                   FunctionTemplateDecl *FunctionTemplate,
                                   const MultiLevelTemplateArgumentList &Args,
                                   unsigned ParamIdx) {
unsigned Idx = 0;
for (auto *PD : FunctionTemplate->getTemplatedDecl()->parameters()) {
  if (PD->isParameterPack()) {
    unsigned NumExpansions =
        S.getNumArgumentsInExpansion(PD->getType(), Args).getValueOr(1);
    if (Idx + NumExpansions > ParamIdx)
      return ParamIdx - Idx;
    Idx += NumExpansions;
  } else {
    if (Idx == ParamIdx)
      return -1; // Not a pack expansion
    ++Idx;
  }
}

llvm_unreachable("parameter index would not be produced from template")__builtin_unreachable();
3546}

3548/// Finish template argument deduction for a function template,
3549/// checking the deduced template arguments for completeness and forming
3550/// the function template specialization.
3551///
3552/// \param OriginalCallArgs If non-NULL, the original call arguments against
3553/// which the deduced argument types should be compared.
3554Sema::TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
  FunctionTemplateDecl *FunctionTemplate,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  unsigned NumExplicitlySpecified, FunctionDecl *&Specialization,
  TemplateDeductionInfo &Info,
  SmallVectorImpl<OriginalCallArg> const *OriginalCallArgs,
  bool PartialOverloading, llvm::function_ref<bool()> CheckNonDependent) {
// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    *this, Sema::ExpressionEvaluationContext::Unevaluated);
SFINAETrap Trap(*this);

// Enter a new template instantiation context while we instantiate the
// actual function declaration.
SmallVector<TemplateArgument, 4> DeducedArgs(Deduced.begin(), Deduced.end());
InstantiatingTemplate Inst(
    *this, Info.getLocation(), FunctionTemplate, DeducedArgs,
    CodeSynthesisContext::DeducedTemplateArgumentSubstitution, Info);
if (Inst.isInvalid())
  return TDK_InstantiationDepth;

ContextRAII SavedContext(*this, FunctionTemplate->getTemplatedDecl());

// C++ [temp.deduct.type]p2:
//   [...] or if any template argument remains neither deduced nor
//   explicitly specified, template argument deduction fails.
SmallVector<TemplateArgument, 4> Builder;
if (auto Result = ConvertDeducedTemplateArguments(
        *this, FunctionTemplate, /*IsDeduced*/true, Deduced, Info, Builder,
        CurrentInstantiationScope, NumExplicitlySpecified,
        PartialOverloading))
  return Result;

// C++ [temp.deduct.call]p10: [DR1391]
//   If deduction succeeds for all parameters that contain
//   template-parameters that participate in template argument deduction,
//   and all template arguments are explicitly specified, deduced, or
//   obtained from default template arguments, remaining parameters are then
//   compared with the corresponding arguments. For each remaining parameter
//   P with a type that was non-dependent before substitution of any
//   explicitly-specified template arguments, if the corresponding argument
//   A cannot be implicitly converted to P, deduction fails.
if (CheckNonDependent())
  return TDK_NonDependentConversionFailure;

// Form the template argument list from the deduced template arguments.
TemplateArgumentList *DeducedArgumentList
  = TemplateArgumentList::CreateCopy(Context, Builder);
Info.reset(DeducedArgumentList);

// Substitute the deduced template arguments into the function template
// declaration to produce the function template specialization.
DeclContext *Owner = FunctionTemplate->getDeclContext();
if (FunctionTemplate->getFriendObjectKind())
  Owner = FunctionTemplate->getLexicalDeclContext();
MultiLevelTemplateArgumentList SubstArgs(*DeducedArgumentList);
Specialization = cast_or_null<FunctionDecl>(
    SubstDecl(FunctionTemplate->getTemplatedDecl(), Owner, SubstArgs));
if (!Specialization || Specialization->isInvalidDecl())
  return TDK_SubstitutionFailure;

assert(Specialization->getPrimaryTemplate()->getCanonicalDecl() ==((void)0)
       FunctionTemplate->getCanonicalDecl())((void)0);

// If the template argument list is owned by the function template
// specialization, release it.
if (Specialization->getTemplateSpecializationArgs() == DeducedArgumentList &&
    !Trap.hasErrorOccurred())
  Info.take();

// There may have been an error that did not prevent us from constructing a
// declaration. Mark the declaration invalid and return with a substitution
// failure.
if (Trap.hasErrorOccurred()) {
  Specialization->setInvalidDecl(true);
  return TDK_SubstitutionFailure;
}

// C++2a [temp.deduct]p5
//   [...] When all template arguments have been deduced [...] all uses of
//   template parameters [...] are replaced with the corresponding deduced
//   or default argument values.
//   [...] If the function template has associated constraints
//   ([temp.constr.decl]), those constraints are checked for satisfaction
//   ([temp.constr.constr]). If the constraints are not satisfied, type
//   deduction fails.
if (!PartialOverloading ||
    (Builder.size() == FunctionTemplate->getTemplateParameters()->size())) {
  if (CheckInstantiatedFunctionTemplateConstraints(Info.getLocation(),
          Specialization, Builder, Info.AssociatedConstraintsSatisfaction))
    return TDK_MiscellaneousDeductionFailure;

  if (!Info.AssociatedConstraintsSatisfaction.IsSatisfied) {
    Info.reset(TemplateArgumentList::CreateCopy(Context, Builder));
    return TDK_ConstraintsNotSatisfied;
  }
}

if (OriginalCallArgs) {
  // C++ [temp.deduct.call]p4:
  //   In general, the deduction process attempts to find template argument
  //   values that will make the deduced A identical to A (after the type A
  //   is transformed as described above). [...]
  llvm::SmallDenseMap<std::pair<unsigned, QualType>, QualType> DeducedATypes;
  for (unsigned I = 0, N = OriginalCallArgs->size(); I != N; ++I) {
    OriginalCallArg OriginalArg = (*OriginalCallArgs)[I];

    auto ParamIdx = OriginalArg.ArgIdx;
    if (ParamIdx >= Specialization->getNumParams())
      // FIXME: This presumably means a pack ended up smaller than we
      // expected while deducing. Should this not result in deduction
      // failure? Can it even happen?
      continue;

    QualType DeducedA;
    if (!OriginalArg.DecomposedParam) {
      // P is one of the function parameters, just look up its substituted
      // type.
      DeducedA = Specialization->getParamDecl(ParamIdx)->getType();
    } else {
      // P is a decomposed element of a parameter corresponding to a
      // braced-init-list argument. Substitute back into P to find the
      // deduced A.
      QualType &CacheEntry =
          DeducedATypes[{ParamIdx, OriginalArg.OriginalParamType}];
      if (CacheEntry.isNull()) {
        ArgumentPackSubstitutionIndexRAII PackIndex(
            *this, getPackIndexForParam(*this, FunctionTemplate, SubstArgs,
                                        ParamIdx));
        CacheEntry =
            SubstType(OriginalArg.OriginalParamType, SubstArgs,
                      Specialization->getTypeSpecStartLoc(),
                      Specialization->getDeclName());
      }
      DeducedA = CacheEntry;
    }

    if (auto TDK =
            CheckOriginalCallArgDeduction(*this, Info, OriginalArg, DeducedA))
      return TDK;
  }
}

// If we suppressed any diagnostics while performing template argument
// deduction, and if we haven't already instantiated this declaration,
// keep track of these diagnostics. They'll be emitted if this specialization
// is actually used.
if (Info.diag_begin() != Info.diag_end()) {
  SuppressedDiagnosticsMap::iterator
    Pos = SuppressedDiagnostics.find(Specialization->getCanonicalDecl());
  if (Pos == SuppressedDiagnostics.end())
      SuppressedDiagnostics[Specialization->getCanonicalDecl()]
        .append(Info.diag_begin(), Info.diag_end());
}

return TDK_Success;
3710}

3712/// Gets the type of a function for template-argument-deducton
3713/// purposes when it's considered as part of an overload set.
3714static QualType GetTypeOfFunction(Sema &S, const OverloadExpr::FindResult &R,
                                FunctionDecl *Fn) {
// We may need to deduce the return type of the function now.
if (S.getLangOpts().CPlusPlus14 && Fn->getReturnType()->isUndeducedType() &&
    S.DeduceReturnType(Fn, R.Expression->getExprLoc(), /*Diagnose*/ false))
  return {};

if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Fn))
  if (Method->isInstance()) {
    // An instance method that's referenced in a form that doesn't
    // look like a member pointer is just invalid.
    if (!R.HasFormOfMemberPointer)
      return {};

    return S.Context.getMemberPointerType(Fn->getType(),
             S.Context.getTypeDeclType(Method->getParent()).getTypePtr());
  }

if (!R.IsAddressOfOperand) return Fn->getType();
return S.Context.getPointerType(Fn->getType());
3734}

3736/// Apply the deduction rules for overload sets.
3737///
3738/// \return the null type if this argument should be treated as an
3739/// undeduced context
3740static QualType
3741ResolveOverloadForDeduction(Sema &S, TemplateParameterList *TemplateParams,
                          Expr *Arg, QualType ParamType,
                          bool ParamWasReference) {

OverloadExpr::FindResult R = OverloadExpr::find(Arg);

OverloadExpr *Ovl = R.Expression;

// C++0x [temp.deduct.call]p4
unsigned TDF = 0;
if (ParamWasReference)
  TDF |= TDF_ParamWithReferenceType;
if (R.IsAddressOfOperand)
  TDF |= TDF_IgnoreQualifiers;

// C++0x [temp.deduct.call]p6:
//   When P is a function type, pointer to function type, or pointer
//   to member function type:

if (!ParamType->isFunctionType() &&
    !ParamType->isFunctionPointerType() &&
    !ParamType->isMemberFunctionPointerType()) {
  if (Ovl->hasExplicitTemplateArgs()) {
    // But we can still look for an explicit specialization.
    if (FunctionDecl *ExplicitSpec
          = S.ResolveSingleFunctionTemplateSpecialization(Ovl))
      return GetTypeOfFunction(S, R, ExplicitSpec);
  }

  DeclAccessPair DAP;
  if (FunctionDecl *Viable =
          S.resolveAddressOfSingleOverloadCandidate(Arg, DAP))
    return GetTypeOfFunction(S, R, Viable);

  return {};
}

// Gather the explicit template arguments, if any.
TemplateArgumentListInfo ExplicitTemplateArgs;
if (Ovl->hasExplicitTemplateArgs())
  Ovl->copyTemplateArgumentsInto(ExplicitTemplateArgs);
QualType Match;
for (UnresolvedSetIterator I = Ovl->decls_begin(),
       E = Ovl->decls_end(); I != E; ++I) {
  NamedDecl *D = (*I)->getUnderlyingDecl();

  if (FunctionTemplateDecl *FunTmpl = dyn_cast<FunctionTemplateDecl>(D)) {
    //   - If the argument is an overload set containing one or more
    //     function templates, the parameter is treated as a
    //     non-deduced context.
    if (!Ovl->hasExplicitTemplateArgs())
      return {};

    // Otherwise, see if we can resolve a function type
    FunctionDecl *Specialization = nullptr;
    TemplateDeductionInfo Info(Ovl->getNameLoc());
    if (S.DeduceTemplateArguments(FunTmpl, &ExplicitTemplateArgs,
                                  Specialization, Info))
      continue;

    D = Specialization;
  }

  FunctionDecl *Fn = cast<FunctionDecl>(D);
  QualType ArgType = GetTypeOfFunction(S, R, Fn);
  if (ArgType.isNull()) continue;

  // Function-to-pointer conversion.
  if (!ParamWasReference && ParamType->isPointerType() &&
      ArgType->isFunctionType())
    ArgType = S.Context.getPointerType(ArgType);

  //   - If the argument is an overload set (not containing function
  //     templates), trial argument deduction is attempted using each
  //     of the members of the set. If deduction succeeds for only one
  //     of the overload set members, that member is used as the
  //     argument value for the deduction. If deduction succeeds for
  //     more than one member of the overload set the parameter is
  //     treated as a non-deduced context.

  // We do all of this in a fresh context per C++0x [temp.deduct.type]p2:
  //   Type deduction is done independently for each P/A pair, and
  //   the deduced template argument values are then combined.
  // So we do not reject deductions which were made elsewhere.
  SmallVector<DeducedTemplateArgument, 8>
    Deduced(TemplateParams->size());
  TemplateDeductionInfo Info(Ovl->getNameLoc());
  Sema::TemplateDeductionResult Result
    = DeduceTemplateArgumentsByTypeMatch(S, TemplateParams, ParamType,
                                         ArgType, Info, Deduced, TDF);
  if (Result) continue;
  if (!Match.isNull())
    return {};
  Match = ArgType;
}

return Match;
3838}

3840/// Perform the adjustments to the parameter and argument types
3841/// described in C++ [temp.deduct.call].
3842///
3843/// \returns true if the caller should not attempt to perform any template
3844/// argument deduction based on this P/A pair because the argument is an
3845/// overloaded function set that could not be resolved.
3846static bool AdjustFunctionParmAndArgTypesForDeduction(
  Sema &S, TemplateParameterList *TemplateParams, unsigned FirstInnerIndex,
  QualType &ParamType, QualType &ArgType, Expr *Arg, unsigned &TDF) {
// C++0x [temp.deduct.call]p3:
//   If P is a cv-qualified type, the top level cv-qualifiers of P's type
//   are ignored for type deduction.
if (ParamType.hasQualifiers())
  ParamType = ParamType.getUnqualifiedType();

//   [...] If P is a reference type, the type referred to by P is
//   used for type deduction.
const ReferenceType *ParamRefType = ParamType->getAs<ReferenceType>();
if (ParamRefType)
  ParamType = ParamRefType->getPointeeType();

// Overload sets usually make this parameter an undeduced context,
// but there are sometimes special circumstances.  Typically
// involving a template-id-expr.
if (ArgType == S.Context.OverloadTy) {
  ArgType = ResolveOverloadForDeduction(S, TemplateParams,
                                        Arg, ParamType,
                                        ParamRefType != nullptr);
  if (ArgType.isNull())
    return true;
}

if (ParamRefType) {
  // If the argument has incomplete array type, try to complete its type.
  if (ArgType->isIncompleteArrayType())
    ArgType = S.getCompletedType(Arg);

  // C++1z [temp.deduct.call]p3:
  //   If P is a forwarding reference and the argument is an lvalue, the type
  //   "lvalue reference to A" is used in place of A for type deduction.
  if (isForwardingReference(QualType(ParamRefType, 0), FirstInnerIndex) &&
      Arg->isLValue()) {
    if (S.getLangOpts().OpenCL  && !ArgType.hasAddressSpace())
      ArgType = S.Context.getAddrSpaceQualType(ArgType, LangAS::opencl_generic);
    ArgType = S.Context.getLValueReferenceType(ArgType);
  }
} else {
  // C++ [temp.deduct.call]p2:
  //   If P is not a reference type:
  //   - If A is an array type, the pointer type produced by the
  //     array-to-pointer standard conversion (4.2) is used in place of
  //     A for type deduction; otherwise,
  if (ArgType->isArrayType())
    ArgType = S.Context.getArrayDecayedType(ArgType);
  //   - If A is a function type, the pointer type produced by the
  //     function-to-pointer standard conversion (4.3) is used in place
  //     of A for type deduction; otherwise,
  else if (ArgType->isFunctionType())
    ArgType = S.Context.getPointerType(ArgType);
  else {
    // - If A is a cv-qualified type, the top level cv-qualifiers of A's
    //   type are ignored for type deduction.
    ArgType = ArgType.getUnqualifiedType();
  }
}

// C++0x [temp.deduct.call]p4:
//   In general, the deduction process attempts to find template argument
//   values that will make the deduced A identical to A (after the type A
//   is transformed as described above). [...]
TDF = TDF_SkipNonDependent;

//     - If the original P is a reference type, the deduced A (i.e., the
//       type referred to by the reference) can be more cv-qualified than
//       the transformed A.
if (ParamRefType)
  TDF |= TDF_ParamWithReferenceType;
//     - The transformed A can be another pointer or pointer to member
//       type that can be converted to the deduced A via a qualification
//       conversion (4.4).
if (ArgType->isPointerType() || ArgType->isMemberPointerType() ||
    ArgType->isObjCObjectPointerType())
  TDF |= TDF_IgnoreQualifiers;
//     - If P is a class and P has the form simple-template-id, then the
//       transformed A can be a derived class of the deduced A. Likewise,
//       if P is a pointer to a class of the form simple-template-id, the
//       transformed A can be a pointer to a derived class pointed to by
//       the deduced A.
if (isSimpleTemplateIdType(ParamType) ||
    (isa<PointerType>(ParamType) &&
     isSimpleTemplateIdType(
         ParamType->castAs<PointerType>()->getPointeeType())))
  TDF |= TDF_DerivedClass;

return false;
3935}

3937static bool
3938hasDeducibleTemplateParameters(Sema &S, FunctionTemplateDecl *FunctionTemplate,
                             QualType T);

3941static Sema::TemplateDeductionResult DeduceTemplateArgumentsFromCallArgument(
  Sema &S, TemplateParameterList *TemplateParams, unsigned FirstInnerIndex,
  QualType ParamType, Expr *Arg, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  SmallVectorImpl<Sema::OriginalCallArg> &OriginalCallArgs,
  bool DecomposedParam, unsigned ArgIdx, unsigned TDF);

3948/// Attempt template argument deduction from an initializer list
3949///        deemed to be an argument in a function call.
3950static Sema::TemplateDeductionResult DeduceFromInitializerList(
  Sema &S, TemplateParameterList *TemplateParams, QualType AdjustedParamType,
  InitListExpr *ILE, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  SmallVectorImpl<Sema::OriginalCallArg> &OriginalCallArgs, unsigned ArgIdx,
  unsigned TDF) {
// C++ [temp.deduct.call]p1: (CWG 1591)
//   If removing references and cv-qualifiers from P gives
//   std::initializer_list<P0> or P0[N] for some P0 and N and the argument is
//   a non-empty initializer list, then deduction is performed instead for
//   each element of the initializer list, taking P0 as a function template
//   parameter type and the initializer element as its argument
//
// We've already removed references and cv-qualifiers here.
if (!ILE->getNumInits())
  return Sema::TDK_Success;

QualType ElTy;
auto *ArrTy = S.Context.getAsArrayType(AdjustedParamType);
if (ArrTy)
  ElTy = ArrTy->getElementType();
else if (!S.isStdInitializerList(AdjustedParamType, &ElTy)) {
  //   Otherwise, an initializer list argument causes the parameter to be
  //   considered a non-deduced context
  return Sema::TDK_Success;
}

// Resolving a core issue: a braced-init-list containing any designators is
// a non-deduced context.
for (Expr *E : ILE->inits())
  if (isa<DesignatedInitExpr>(E))
    return Sema::TDK_Success;

// Deduction only needs to be done for dependent types.
if (ElTy->isDependentType()) {
  for (Expr *E : ILE->inits()) {
    if (auto Result = DeduceTemplateArgumentsFromCallArgument(
            S, TemplateParams, 0, ElTy, E, Info, Deduced, OriginalCallArgs, true,
            ArgIdx, TDF))
      return Result;
  }
}

//   in the P0[N] case, if N is a non-type template parameter, N is deduced
//   from the length of the initializer list.
if (auto *DependentArrTy = dyn_cast_or_null<DependentSizedArrayType>(ArrTy)) {
  // Determine the array bound is something we can deduce.
  if (const NonTypeTemplateParmDecl *NTTP =
          getDeducedParameterFromExpr(Info, DependentArrTy->getSizeExpr())) {
    // We can perform template argument deduction for the given non-type
    // template parameter.
    // C++ [temp.deduct.type]p13:
    //   The type of N in the type T[N] is std::size_t.
    QualType T = S.Context.getSizeType();
    llvm::APInt Size(S.Context.getIntWidth(T), ILE->getNumInits());
    if (auto Result = DeduceNonTypeTemplateArgument(
            S, TemplateParams, NTTP, llvm::APSInt(Size), T,
            /*ArrayBound=*/true, Info, Deduced))
      return Result;
  }
}

return Sema::TDK_Success;
4013}

4015/// Perform template argument deduction per [temp.deduct.call] for a
4016///        single parameter / argument pair.
4017static Sema::TemplateDeductionResult DeduceTemplateArgumentsFromCallArgument(
  Sema &S, TemplateParameterList *TemplateParams, unsigned FirstInnerIndex,
  QualType ParamType, Expr *Arg, TemplateDeductionInfo &Info,
  SmallVectorImpl<DeducedTemplateArgument> &Deduced,
  SmallVectorImpl<Sema::OriginalCallArg> &OriginalCallArgs,
  bool DecomposedParam, unsigned ArgIdx, unsigned TDF) {
QualType ArgType = Arg->getType();
QualType OrigParamType = ParamType;

//   If P is a reference type [...]
//   If P is a cv-qualified type [...]
if (AdjustFunctionParmAndArgTypesForDeduction(
        S, TemplateParams, FirstInnerIndex, ParamType, ArgType, Arg, TDF))
  return Sema::TDK_Success;

//   If [...] the argument is a non-empty initializer list [...]
if (InitListExpr *ILE = dyn_cast<InitListExpr>(Arg))
  return DeduceFromInitializerList(S, TemplateParams, ParamType, ILE, Info,
                                   Deduced, OriginalCallArgs, ArgIdx, TDF);

//   [...] the deduction process attempts to find template argument values
//   that will make the deduced A identical to A
//
// Keep track of the argument type and corresponding parameter index,
// so we can check for compatibility between the deduced A and A.
OriginalCallArgs.push_back(
    Sema::OriginalCallArg(OrigParamType, DecomposedParam, ArgIdx, ArgType));
return DeduceTemplateArgumentsByTypeMatch(S, TemplateParams, ParamType,
                                          ArgType, Info, Deduced, TDF);
4046}

4048/// Perform template argument deduction from a function call
4049/// (C++ [temp.deduct.call]).
4050///
4051/// \param FunctionTemplate the function template for which we are performing
4052/// template argument deduction.
4053///
4054/// \param ExplicitTemplateArgs the explicit template arguments provided
4055/// for this call.
4056///
4057/// \param Args the function call arguments
4058///
4059/// \param Specialization if template argument deduction was successful,
4060/// this will be set to the function template specialization produced by
4061/// template argument deduction.
4062///
4063/// \param Info the argument will be updated to provide additional information
4064/// about template argument deduction.
4065///
4066/// \param CheckNonDependent A callback to invoke to check conversions for
4067/// non-dependent parameters, between deduction and substitution, per DR1391.
4068/// If this returns true, substitution will be skipped and we return
4069/// TDK_NonDependentConversionFailure. The callback is passed the parameter
4070/// types (after substituting explicit template arguments).
4071///
4072/// \returns the result of template argument deduction.
4073Sema::TemplateDeductionResult Sema::DeduceTemplateArguments(
  FunctionTemplateDecl *FunctionTemplate,
  TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
  FunctionDecl *&Specialization, TemplateDeductionInfo &Info,
  bool PartialOverloading,
  llvm::function_ref<bool(ArrayRef<QualType>)> CheckNonDependent) {
if (FunctionTemplate->isInvalidDecl())
  return TDK_Invalid;

FunctionDecl *Function = FunctionTemplate->getTemplatedDecl();
unsigned NumParams = Function->getNumParams();

unsigned FirstInnerIndex = getFirstInnerIndex(FunctionTemplate);

// C++ [temp.deduct.call]p1:
//   Template argument deduction is done by comparing each function template
//   parameter type (call it P) with the type of the corresponding argument
//   of the call (call it A) as described below.
if (Args.size() < Function->getMinRequiredArguments() && !PartialOverloading)
  return TDK_TooFewArguments;
else if (TooManyArguments(NumParams, Args.size(), PartialOverloading)) {
  const auto *Proto = Function->getType()->castAs<FunctionProtoType>();
  if (Proto->isTemplateVariadic())
    /* Do nothing */;
  else if (!Proto->isVariadic())
    return TDK_TooManyArguments;
}

// The types of the parameters from which we will perform template argument
// deduction.
LocalInstantiationScope InstScope(*this);
TemplateParameterList *TemplateParams
  = FunctionTemplate->getTemplateParameters();
SmallVector<DeducedTemplateArgument, 4> Deduced;
SmallVector<QualType, 8> ParamTypes;
unsigned NumExplicitlySpecified = 0;
if (ExplicitTemplateArgs) {
  TemplateDeductionResult Result;
  runWithSufficientStackSpace(Info.getLocation(), [&] {
    Result = SubstituteExplicitTemplateArguments(
        FunctionTemplate, *ExplicitTemplateArgs, Deduced, ParamTypes, nullptr,
        Info);
  });
  if (Result)
    return Result;

  NumExplicitlySpecified = Deduced.size();
} else {
  // Just fill in the parameter types from the function declaration.
  for (unsigned I = 0; I != NumParams; ++I)
    ParamTypes.push_back(Function->getParamDecl(I)->getType());
}

SmallVector<OriginalCallArg, 8> OriginalCallArgs;

// Deduce an argument of type ParamType from an expression with index ArgIdx.
auto DeduceCallArgument = [&](QualType ParamType, unsigned ArgIdx) {
  // C++ [demp.deduct.call]p1: (DR1391)
  //   Template argument deduction is done by comparing each function template
  //   parameter that contains template-parameters that participate in
  //   template argument deduction ...
  if (!hasDeducibleTemplateParameters(*this, FunctionTemplate, ParamType))
    return Sema::TDK_Success;

  //   ... with the type of the corresponding argument
  return DeduceTemplateArgumentsFromCallArgument(
      *this, TemplateParams, FirstInnerIndex, ParamType, Args[ArgIdx], Info, Deduced,
      OriginalCallArgs, /*Decomposed*/false, ArgIdx, /*TDF*/ 0);
};

// Deduce template arguments from the function parameters.
Deduced.resize(TemplateParams->size());
SmallVector<QualType, 8> ParamTypesForArgChecking;
for (unsigned ParamIdx = 0, NumParamTypes = ParamTypes.size(), ArgIdx = 0;
     ParamIdx != NumParamTypes; ++ParamIdx) {
  QualType ParamType = ParamTypes[ParamIdx];

  const PackExpansionType *ParamExpansion =
      dyn_cast<PackExpansionType>(ParamType);
  if (!ParamExpansion) {
    // Simple case: matching a function parameter to a function argument.
    if (ArgIdx >= Args.size())
      break;

    ParamTypesForArgChecking.push_back(ParamType);
    if (auto Result = DeduceCallArgument(ParamType, ArgIdx++))
      return Result;

    continue;
  }

  QualType ParamPattern = ParamExpansion->getPattern();
  PackDeductionScope PackScope(*this, TemplateParams, Deduced, Info,
                               ParamPattern);

  // C++0x [temp.deduct.call]p1:
  //   For a function parameter pack that occurs at the end of the
  //   parameter-declaration-list, the type A of each remaining argument of
  //   the call is compared with the type P of the declarator-id of the
  //   function parameter pack. Each comparison deduces template arguments
  //   for subsequent positions in the template parameter packs expanded by
  //   the function parameter pack. When a function parameter pack appears
  //   in a non-deduced context [not at the end of the list], the type of
  //   that parameter pack is never deduced.
  //
  // FIXME: The above rule allows the size of the parameter pack to change
  // after we skip it (in the non-deduced case). That makes no sense, so
  // we instead notionally deduce the pack against N arguments, where N is
  // the length of the explicitly-specified pack if it's expanded by the
  // parameter pack and 0 otherwise, and we treat each deduction as a
  // non-deduced context.
  if (ParamIdx + 1 == NumParamTypes || PackScope.hasFixedArity()) {
    for (; ArgIdx < Args.size() && PackScope.hasNextElement();
         PackScope.nextPackElement(), ++ArgIdx) {
      ParamTypesForArgChecking.push_back(ParamPattern);
      if (auto Result = DeduceCallArgument(ParamPattern, ArgIdx))
        return Result;
    }
  } else {
    // If the parameter type contains an explicitly-specified pack that we
    // could not expand, skip the number of parameters notionally created
    // by the expansion.
    Optional<unsigned> NumExpansions = ParamExpansion->getNumExpansions();
    if (NumExpansions && !PackScope.isPartiallyExpanded()) {
      for (unsigned I = 0; I != *NumExpansions && ArgIdx < Args.size();
           ++I, ++ArgIdx) {
        ParamTypesForArgChecking.push_back(ParamPattern);
        // FIXME: Should we add OriginalCallArgs for these? What if the
        // corresponding argument is a list?
        PackScope.nextPackElement();
      }
    }
  }

  // Build argument packs for each of the parameter packs expanded by this
  // pack expansion.
  if (auto Result = PackScope.finish())
    return Result;
}

// Capture the context in which the function call is made. This is the context
// that is needed when the accessibility of template arguments is checked.
DeclContext *CallingCtx = CurContext;

TemplateDeductionResult Result;
runWithSufficientStackSpace(Info.getLocation(), [&] {
  Result = FinishTemplateArgumentDeduction(
      FunctionTemplate, Deduced, NumExplicitlySpecified, Specialization, Info,
      &OriginalCallArgs, PartialOverloading, [&, CallingCtx]() {
        ContextRAII SavedContext(*this, CallingCtx);
        return CheckNonDependent(ParamTypesForArgChecking);
      });
});
return Result;
4227}

4229QualType Sema::adjustCCAndNoReturn(QualType ArgFunctionType,
                                 QualType FunctionType,
                                 bool AdjustExceptionSpec) {
if (ArgFunctionType.isNull())
  return ArgFunctionType;

const auto *FunctionTypeP = FunctionType->castAs<FunctionProtoType>();
const auto *ArgFunctionTypeP = ArgFunctionType->castAs<FunctionProtoType>();
FunctionProtoType::ExtProtoInfo EPI = ArgFunctionTypeP->getExtProtoInfo();
bool Rebuild = false;

CallingConv CC = FunctionTypeP->getCallConv();
if (EPI.ExtInfo.getCC() != CC) {
  EPI.ExtInfo = EPI.ExtInfo.withCallingConv(CC);
  Rebuild = true;
}

bool NoReturn = FunctionTypeP->getNoReturnAttr();
if (EPI.ExtInfo.getNoReturn() != NoReturn) {
  EPI.ExtInfo = EPI.ExtInfo.withNoReturn(NoReturn);
  Rebuild = true;
}

if (AdjustExceptionSpec && (FunctionTypeP->hasExceptionSpec() ||
                            ArgFunctionTypeP->hasExceptionSpec())) {
  EPI.ExceptionSpec = FunctionTypeP->getExtProtoInfo().ExceptionSpec;
  Rebuild = true;
}

if (!Rebuild)
  return ArgFunctionType;

return Context.getFunctionType(ArgFunctionTypeP->getReturnType(),
                               ArgFunctionTypeP->getParamTypes(), EPI);
4263}

4265/// Deduce template arguments when taking the address of a function
4266/// template (C++ [temp.deduct.funcaddr]) or matching a specialization to
4267/// a template.
4268///
4269/// \param FunctionTemplate the function template for which we are performing
4270/// template argument deduction.
4271///
4272/// \param ExplicitTemplateArgs the explicitly-specified template
4273/// arguments.
4274///
4275/// \param ArgFunctionType the function type that will be used as the
4276/// "argument" type (A) when performing template argument deduction from the
4277/// function template's function type. This type may be NULL, if there is no
4278/// argument type to compare against, in C++0x [temp.arg.explicit]p3.
4279///
4280/// \param Specialization if template argument deduction was successful,
4281/// this will be set to the function template specialization produced by
4282/// template argument deduction.
4283///
4284/// \param Info the argument will be updated to provide additional information
4285/// about template argument deduction.
4286///
4287/// \param IsAddressOfFunction If \c true, we are deducing as part of taking
4288/// the address of a function template per [temp.deduct.funcaddr] and
4289/// [over.over]. If \c false, we are looking up a function template
4290/// specialization based on its signature, per [temp.deduct.decl].
4291///
4292/// \returns the result of template argument deduction.
4293Sema::TemplateDeductionResult Sema::DeduceTemplateArguments(
  FunctionTemplateDecl *FunctionTemplate,
  TemplateArgumentListInfo *ExplicitTemplateArgs, QualType ArgFunctionType,
  FunctionDecl *&Specialization, TemplateDeductionInfo &Info,
  bool IsAddressOfFunction) {
if (FunctionTemplate->isInvalidDecl())
  return TDK_Invalid;

FunctionDecl *Function = FunctionTemplate->getTemplatedDecl();
TemplateParameterList *TemplateParams
  = FunctionTemplate->getTemplateParameters();
QualType FunctionType = Function->getType();

// Substitute any explicit template arguments.
LocalInstantiationScope InstScope(*this);
SmallVector<DeducedTemplateArgument, 4> Deduced;
unsigned NumExplicitlySpecified = 0;
SmallVector<QualType, 4> ParamTypes;
if (ExplicitTemplateArgs) {
  TemplateDeductionResult Result;
  runWithSufficientStackSpace(Info.getLocation(), [&] {
    Result = SubstituteExplicitTemplateArguments(
1
Calling 'Sema::SubstituteExplicitTemplateArguments'→
        FunctionTemplate, *ExplicitTemplateArgs, Deduced, ParamTypes,
        &FunctionType, Info);
  });
  if (Result)
    return Result;

  NumExplicitlySpecified = Deduced.size();
}

// When taking the address of a function, we require convertibility of
// the resulting function type. Otherwise, we allow arbitrary mismatches
// of calling convention and noreturn.
if (!IsAddressOfFunction)
  ArgFunctionType = adjustCCAndNoReturn(ArgFunctionType, FunctionType,
                                        /*AdjustExceptionSpec*/false);

// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    *this, Sema::ExpressionEvaluationContext::Unevaluated);
SFINAETrap Trap(*this);

Deduced.resize(TemplateParams->size());

// If the function has a deduced return type, substitute it for a dependent
// type so that we treat it as a non-deduced context in what follows. If we
// are looking up by signature, the signature type should also have a deduced
// return type, which we instead expect to exactly match.
bool HasDeducedReturnType = false;
if (getLangOpts().CPlusPlus14 && IsAddressOfFunction &&
    Function->getReturnType()->getContainedAutoType()) {
  FunctionType = SubstAutoType(FunctionType, Context.DependentTy);
  HasDeducedReturnType = true;
}

if (!ArgFunctionType.isNull()) {
  unsigned TDF =
      TDF_TopLevelParameterTypeList | TDF_AllowCompatibleFunctionType;
  // Deduce template arguments from the function type.
  if (TemplateDeductionResult Result
        = DeduceTemplateArgumentsByTypeMatch(*this, TemplateParams,
                                             FunctionType, ArgFunctionType,
                                             Info, Deduced, TDF))
    return Result;
}

TemplateDeductionResult Result;
runWithSufficientStackSpace(Info.getLocation(), [&] {
  Result = FinishTemplateArgumentDeduction(FunctionTemplate, Deduced,
                                           NumExplicitlySpecified,
                                           Specialization, Info);
});
if (Result)
  return Result;

// If the function has a deduced return type, deduce it now, so we can check
// that the deduced function type matches the requested type.
if (HasDeducedReturnType &&
    Specialization->getReturnType()->isUndeducedType() &&
    DeduceReturnType(Specialization, Info.getLocation(), false))
  return TDK_MiscellaneousDeductionFailure;

// If the function has a dependent exception specification, resolve it now,
// so we can check that the exception specification matches.
auto *SpecializationFPT =
    Specialization->getType()->castAs<FunctionProtoType>();
if (getLangOpts().CPlusPlus17 &&
    isUnresolvedExceptionSpec(SpecializationFPT->getExceptionSpecType()) &&
    !ResolveExceptionSpec(Info.getLocation(), SpecializationFPT))
  return TDK_MiscellaneousDeductionFailure;

// Adjust the exception specification of the argument to match the
// substituted and resolved type we just formed. (Calling convention and
// noreturn can't be dependent, so we don't actually need this for them
// right now.)
QualType SpecializationType = Specialization->getType();
if (!IsAddressOfFunction)
  ArgFunctionType = adjustCCAndNoReturn(ArgFunctionType, SpecializationType,
                                        /*AdjustExceptionSpec*/true);

// If the requested function type does not match the actual type of the
// specialization with respect to arguments of compatible pointer to function
// types, template argument deduction fails.
if (!ArgFunctionType.isNull()) {
  if (IsAddressOfFunction &&
      !isSameOrCompatibleFunctionType(
          Context.getCanonicalType(SpecializationType),
          Context.getCanonicalType(ArgFunctionType)))
    return TDK_MiscellaneousDeductionFailure;

  if (!IsAddressOfFunction &&
      !Context.hasSameType(SpecializationType, ArgFunctionType))
    return TDK_MiscellaneousDeductionFailure;
}

return TDK_Success;
4410}

4412/// Deduce template arguments for a templated conversion
4413/// function (C++ [temp.deduct.conv]) and, if successful, produce a
4414/// conversion function template specialization.
4415Sema::TemplateDeductionResult
4416Sema::DeduceTemplateArguments(FunctionTemplateDecl *ConversionTemplate,
                            QualType ToType,
                            CXXConversionDecl *&Specialization,
                            TemplateDeductionInfo &Info) {
if (ConversionTemplate->isInvalidDecl())
  return TDK_Invalid;

CXXConversionDecl *ConversionGeneric
  = cast<CXXConversionDecl>(ConversionTemplate->getTemplatedDecl());

QualType FromType = ConversionGeneric->getConversionType();

// Canonicalize the types for deduction.
QualType P = Context.getCanonicalType(FromType);
QualType A = Context.getCanonicalType(ToType);

// C++0x [temp.deduct.conv]p2:
//   If P is a reference type, the type referred to by P is used for
//   type deduction.
if (const ReferenceType *PRef = P->getAs<ReferenceType>())
  P = PRef->getPointeeType();

// C++0x [temp.deduct.conv]p4:
//   [...] If A is a reference type, the type referred to by A is used
//   for type deduction.
if (const ReferenceType *ARef = A->getAs<ReferenceType>()) {
  A = ARef->getPointeeType();
  // We work around a defect in the standard here: cv-qualifiers are also
  // removed from P and A in this case, unless P was a reference type. This
  // seems to mostly match what other compilers are doing.
  if (!FromType->getAs<ReferenceType>()) {
    A = A.getUnqualifiedType();
    P = P.getUnqualifiedType();
  }

// C++ [temp.deduct.conv]p3:
//
//   If A is not a reference type:
} else {
  assert(!A->isReferenceType() && "Reference types were handled above")((void)0);

  //   - If P is an array type, the pointer type produced by the
  //     array-to-pointer standard conversion (4.2) is used in place
  //     of P for type deduction; otherwise,
  if (P->isArrayType())
    P = Context.getArrayDecayedType(P);
  //   - If P is a function type, the pointer type produced by the
  //     function-to-pointer standard conversion (4.3) is used in
  //     place of P for type deduction; otherwise,
  else if (P->isFunctionType())
    P = Context.getPointerType(P);
  //   - If P is a cv-qualified type, the top level cv-qualifiers of
  //     P's type are ignored for type deduction.
  else
    P = P.getUnqualifiedType();

  // C++0x [temp.deduct.conv]p4:
  //   If A is a cv-qualified type, the top level cv-qualifiers of A's
  //   type are ignored for type deduction. If A is a reference type, the type
  //   referred to by A is used for type deduction.
  A = A.getUnqualifiedType();
}

// Unevaluated SFINAE context.
EnterExpressionEvaluationContext Unevaluated(
    *this, Sema::ExpressionEvaluationContext::Unevaluated);
SFINAETrap Trap(*this);

// C++ [temp.deduct.conv]p1:
//   Template argument deduction is done by comparing the return
//   type of the template conversion function (call it P) with the
//   type that is required as the result of the conversion (call it
//   A) as described in 14.8.2.4.
TemplateParameterList *TemplateParams
  = ConversionTemplate->getTemplateParameters();
SmallVector<DeducedTemplateArgument, 4> Deduced;
Deduced.resize(TemplateParams->size());

// C++0x [temp.deduct.conv]p4:
//   In general, the deduction process attempts to find template
//   argument values that will make the deduced A identical to
//   A. However, there are two cases that allow a difference:
unsigned TDF = 0;
//     - If the original A is a reference type, A can be more
//       cv-qualified than the deduced A (i.e., the type referred to
//       by the reference)
if (ToType->isReferenceType())
  TDF |= TDF_ArgWithReferenceType;
//     - The deduced A can be another pointer or pointer to member
//       type that can be converted to A via a qualification
//       conversion.
//
// (C++0x [temp.deduct.conv]p6 clarifies that this only happens when
// both P and A are pointers or member pointers. In this case, we
// just ignore cv-qualifiers completely).
if ((P->isPointerType() && A->isPointerType()) ||
    (P->isMemberPointerType() && A->isMemberPointerType()))
  TDF |= TDF_IgnoreQualifiers;
if (TemplateDeductionResult Result
      = DeduceTemplateArgumentsByTypeMatch(*this, TemplateParams,
                                           P, A, Info, Deduced, TDF))
  return Result;

// Create an Instantiation Scope for finalizing the operator.
LocalInstantiationScope InstScope(*this);
// Finish template argument deduction.
FunctionDecl *ConversionSpecialized = nullptr;
TemplateDeductionResult Result;
runWithSufficientStackSpace(Info.getLocation(), [&] {
  Result = FinishTemplateArgumentDeduction(ConversionTemplate, Deduced, 0,
                                           ConversionSpecialized, Info);
});
Specialization = cast_or_null<CXXConversionDecl>(ConversionSpecialized);
return Result;
4530}

4532/// Deduce template arguments for a function template when there is
4533/// nothing to deduce against (C++0x [temp.arg.explicit]p3).
4534///
4535/// \param FunctionTemplate the function template for which we are performing
4536/// template argument deduction.
4537///
4538/// \param ExplicitTemplateArgs the explicitly-specified template
4539/// arguments.
4540///
4541/// \param Specialization if template argument deduction was successful,
4542/// this will be set to the function template specialization produced by
4543/// template argument deduction.
4544///
4545/// \param Info the argument will be updated to provide additional information
4546/// about template argument deduction.
4547///
4548/// \param IsAddressOfFunction If \c true, we are deducing as part of taking
4549/// the address of a function template in a context where we do not have a
4550/// target type, per [over.over]. If \c false, we are looking up a function
4551/// template specialization based on its signature, which only happens when
4552/// deducing a function parameter type from an argument that is a template-id
4553/// naming a function template specialization.
4554///
4555/// \returns the result of template argument deduction.
4556Sema::TemplateDeductionResult Sema::DeduceTemplateArguments(
  FunctionTemplateDecl *FunctionTemplate,
  TemplateArgumentListInfo *ExplicitTemplateArgs,
  FunctionDecl *&Specialization, TemplateDeductionInfo &Info,
  bool IsAddressOfFunction) {
return DeduceTemplateArguments(FunctionTemplate, ExplicitTemplateArgs,
                               QualType(), Specialization, Info,
                               IsAddressOfFunction);
4564}

4566namespace {
struct DependentAuto { bool IsPack; };

/// Substitute the 'auto' specifier or deduced template specialization type
/// specifier within a type for a given replacement type.
class SubstituteDeducedTypeTransform :
    public TreeTransform<SubstituteDeducedTypeTransform> {
  QualType Replacement;
  bool ReplacementIsPack;
  bool UseTypeSugar;

public:
  SubstituteDeducedTypeTransform(Sema &SemaRef, DependentAuto DA)
      : TreeTransform<SubstituteDeducedTypeTransform>(SemaRef), Replacement(),
        ReplacementIsPack(DA.IsPack), UseTypeSugar(true) {}

  SubstituteDeducedTypeTransform(Sema &SemaRef, QualType Replacement,
                                 bool UseTypeSugar = true)
      : TreeTransform<SubstituteDeducedTypeTransform>(SemaRef),
        Replacement(Replacement), ReplacementIsPack(false),
        UseTypeSugar(UseTypeSugar) {}

  QualType TransformDesugared(TypeLocBuilder &TLB, DeducedTypeLoc TL) {
    assert(isa<TemplateTypeParmType>(Replacement) &&((void)0)
           "unexpected unsugared replacement kind")((void)0);
    QualType Result = Replacement;
    TemplateTypeParmTypeLoc NewTL = TLB.push<TemplateTypeParmTypeLoc>(Result);
    NewTL.setNameLoc(TL.getNameLoc());
    return Result;
  }

  QualType TransformAutoType(TypeLocBuilder &TLB, AutoTypeLoc TL) {
    // If we're building the type pattern to deduce against, don't wrap the
    // substituted type in an AutoType. Certain template deduction rules
    // apply only when a template type parameter appears directly (and not if
    // the parameter is found through desugaring). For instance:
    //   auto &&lref = lvalue;
    // must transform into "rvalue reference to T" not "rvalue reference to
    // auto type deduced as T" in order for [temp.deduct.call]p3 to apply.
    //
    // FIXME: Is this still necessary?
    if (!UseTypeSugar)
      return TransformDesugared(TLB, TL);

    QualType Result = SemaRef.Context.getAutoType(
        Replacement, TL.getTypePtr()->getKeyword(), Replacement.isNull(),
        ReplacementIsPack, TL.getTypePtr()->getTypeConstraintConcept(),
        TL.getTypePtr()->getTypeConstraintArguments());
    auto NewTL = TLB.push<AutoTypeLoc>(Result);
    NewTL.copy(TL);
    return Result;
  }

  QualType TransformDeducedTemplateSpecializationType(
      TypeLocBuilder &TLB, DeducedTemplateSpecializationTypeLoc TL) {
    if (!UseTypeSugar)
      return TransformDesugared(TLB, TL);

    QualType Result = SemaRef.Context.getDeducedTemplateSpecializationType(
        TL.getTypePtr()->getTemplateName(),
        Replacement, Replacement.isNull());
    auto NewTL = TLB.push<DeducedTemplateSpecializationTypeLoc>(Result);
    NewTL.setNameLoc(TL.getNameLoc());
    return Result;
  }

  ExprResult TransformLambdaExpr(LambdaExpr *E) {
    // Lambdas never need to be transformed.
    return E;
  }

  QualType Apply(TypeLoc TL) {
    // Create some scratch storage for the transformed type locations.
    // FIXME: We're just going to throw this information away. Don't build it.
    TypeLocBuilder TLB;
    TLB.reserve(TL.getFullDataSize());
    return TransformType(TLB, TL);
  }
};

4646} // namespace

4648Sema::DeduceAutoResult
4649Sema::DeduceAutoType(TypeSourceInfo *Type, Expr *&Init, QualType &Result,
                   Optional<unsigned> DependentDeductionDepth,
                   bool IgnoreConstraints) {
return DeduceAutoType(Type->getTypeLoc(), Init, Result,
                      DependentDeductionDepth, IgnoreConstraints);
4654}

4656/// Attempt to produce an informative diagostic explaining why auto deduction
4657/// failed.
4658/// \return \c true if diagnosed, \c false if not.
4659static bool diagnoseAutoDeductionFailure(Sema &S,
                                       Sema::TemplateDeductionResult TDK,
                                       TemplateDeductionInfo &Info,
                                       ArrayRef<SourceRange> Ranges) {
switch (TDK) {
case Sema::TDK_Inconsistent: {
  // Inconsistent deduction means we were deducing from an initializer list.
  auto D = S.Diag(Info.getLocation(), diag::err_auto_inconsistent_deduction);
  D << Info.FirstArg << Info.SecondArg;
  for (auto R : Ranges)
    D << R;
  return true;
}

// FIXME: Are there other cases for which a custom diagnostic is more useful
// than the basic "types don't match" diagnostic?

default:
  return false;
}
4679}

4681static Sema::DeduceAutoResult
4682CheckDeducedPlaceholderConstraints(Sema &S, const AutoType &Type,
                                 AutoTypeLoc TypeLoc, QualType Deduced) {
ConstraintSatisfaction Satisfaction;
ConceptDecl *Concept = Type.getTypeConstraintConcept();
TemplateArgumentListInfo TemplateArgs(TypeLoc.getLAngleLoc(),
                                      TypeLoc.getRAngleLoc());
TemplateArgs.addArgument(
    TemplateArgumentLoc(TemplateArgument(Deduced),
                        S.Context.getTrivialTypeSourceInfo(
                            Deduced, TypeLoc.getNameLoc())));
for (unsigned I = 0, C = TypeLoc.getNumArgs(); I != C; ++I)
  TemplateArgs.addArgument(TypeLoc.getArgLoc(I));

llvm::SmallVector<TemplateArgument, 4> Converted;
if (S.CheckTemplateArgumentList(Concept, SourceLocation(), TemplateArgs,
                                /*PartialTemplateArgs=*/false, Converted))
  return Sema::DAR_FailedAlreadyDiagnosed;
if (S.CheckConstraintSatisfaction(Concept, {Concept->getConstraintExpr()},
                                  Converted, TypeLoc.getLocalSourceRange(),
                                  Satisfaction))
  return Sema::DAR_FailedAlreadyDiagnosed;
if (!Satisfaction.IsSatisfied) {
  std::string Buf;
  llvm::raw_string_ostream OS(Buf);
  OS << "'" << Concept->getName();
  if (TypeLoc.hasExplicitTemplateArgs()) {
    printTemplateArgumentList(
        OS, Type.getTypeConstraintArguments(), S.getPrintingPolicy(),
        Type.getTypeConstraintConcept()->getTemplateParameters());
  }
  OS << "'";
  OS.flush();
  S.Diag(TypeLoc.getConceptNameLoc(),
         diag::err_placeholder_constraints_not_satisfied)
       << Deduced << Buf << TypeLoc.getLocalSourceRange();
  S.DiagnoseUnsatisfiedConstraint(Satisfaction);
  return Sema::DAR_FailedAlreadyDiagnosed;
}
return Sema::DAR_Succeeded;
4721}

4723/// Deduce the type for an auto type-specifier (C++11 [dcl.spec.auto]p6)
4724///
4725/// Note that this is done even if the initializer is dependent. (This is
4726/// necessary to support partial ordering of templates using 'auto'.)
4727/// A dependent type will be produced when deducing from a dependent type.
4728///
4729/// \param Type the type pattern using the auto type-specifier.
4730/// \param Init the initializer for the variable whose type is to be deduced.
4731/// \param Result if type deduction was successful, this will be set to the
4732///        deduced type.
4733/// \param DependentDeductionDepth Set if we should permit deduction in
4734///        dependent cases. This is necessary for template partial ordering with
4735///        'auto' template parameters. The value specified is the template
4736///        parameter depth at which we should perform 'auto' deduction.
4737/// \param IgnoreConstraints Set if we should not fail if the deduced type does
4738///                          not satisfy the type-constraint in the auto type.
4739Sema::DeduceAutoResult
4740Sema::DeduceAutoType(TypeLoc Type, Expr *&Init, QualType &Result,
                   Optional<unsigned> DependentDeductionDepth,
                   bool IgnoreConstraints) {
if (Init->containsErrors())
  return DAR_FailedAlreadyDiagnosed;
if (Init->getType()->isNonOverloadPlaceholderType()) {
  ExprResult NonPlaceholder = CheckPlaceholderExpr(Init);
  if (NonPlaceholder.isInvalid())
    return DAR_FailedAlreadyDiagnosed;
  Init = NonPlaceholder.get();
}

DependentAuto DependentResult = {
    /*.IsPack = */ (bool)Type.getAs<PackExpansionTypeLoc>()};

if (!DependentDeductionDepth &&
    (Type.getType()->isDependentType() || Init->isTypeDependent() ||
     Init->containsUnexpandedParameterPack())) {
  Result = SubstituteDeducedTypeTransform(*this, DependentResult).Apply(Type);
  assert(!Result.isNull() && "substituting DependentTy can't fail")((void)0);
  return DAR_Succeeded;
}

// Find the depth of template parameter to synthesize.
unsigned Depth = DependentDeductionDepth.getValueOr(0);

// If this is a 'decltype(auto)' specifier, do the decltype dance.
// Since 'decltype(auto)' can only occur at the top of the type, we
// don't need to go digging for it.
if (const AutoType *AT = Type.getType()->getAs<AutoType>()) {
  if (AT->isDecltypeAuto()) {
    if (isa<InitListExpr>(Init)) {
      Diag(Init->getBeginLoc(), diag::err_decltype_auto_initializer_list);
      return DAR_FailedAlreadyDiagnosed;
    }

    ExprResult ER = CheckPlaceholderExpr(Init);
    if (ER.isInvalid())
      return DAR_FailedAlreadyDiagnosed;
    Init = ER.get();
    QualType Deduced = BuildDecltypeType(Init, Init->getBeginLoc(), false);
    if (Deduced.isNull())
      return DAR_FailedAlreadyDiagnosed;
    // FIXME: Support a non-canonical deduced type for 'auto'.
    Deduced = Context.getCanonicalType(Deduced);
    if (AT->isConstrained() && !IgnoreConstraints) {
      auto ConstraintsResult =
          CheckDeducedPlaceholderConstraints(*this, *AT,
                                             Type.getContainedAutoTypeLoc(),
                                             Deduced);
      if (ConstraintsResult != DAR_Succeeded)
        return ConstraintsResult;
    }
    Result = SubstituteDeducedTypeTransform(*this, Deduced).Apply(Type);
    if (Result.isNull())
      return DAR_FailedAlreadyDiagnosed;
    return DAR_Succeeded;
  } else if (!getLangOpts().CPlusPlus) {
    if (isa<InitListExpr>(Init)) {
      Diag(Init->getBeginLoc(), diag::err_auto_init_list_from_c);
      return DAR_FailedAlreadyDiagnosed;
    }
  }
}

SourceLocation Loc = Init->getExprLoc();

LocalInstantiationScope InstScope(*this);

// Build template<class TemplParam> void Func(FuncParam);
TemplateTypeParmDecl *TemplParam = TemplateTypeParmDecl::Create(
    Context, nullptr, SourceLocation(), Loc, Depth, 0, nullptr, false, false,
    false);
QualType TemplArg = QualType(TemplParam->getTypeForDecl(), 0);
NamedDecl *TemplParamPtr = TemplParam;
FixedSizeTemplateParameterListStorage<1, false> TemplateParamsSt(
    Context, Loc, Loc, TemplParamPtr, Loc, nullptr);

QualType FuncParam =
    SubstituteDeducedTypeTransform(*this, TemplArg, /*UseTypeSugar*/false)
        .Apply(Type);
assert(!FuncParam.isNull() &&((void)0)
       "substituting template parameter for 'auto' failed")((void)0);

// Deduce type of TemplParam in Func(Init)
SmallVector<DeducedTemplateArgument, 1> Deduced;
Deduced.resize(1);

TemplateDeductionInfo Info(Loc, Depth);

// If deduction failed, don't diagnose if the initializer is dependent; it
// might acquire a matching type in the instantiation.
auto DeductionFailed = [&](TemplateDeductionResult TDK,
                           ArrayRef<SourceRange> Ranges) -> DeduceAutoResult {
  if (Init->isTypeDependent()) {
    Result =
        SubstituteDeducedTypeTransform(*this, DependentResult).Apply(Type);
    assert(!Result.isNull() && "substituting DependentTy can't fail")((void)0);
    return DAR_Succeeded;
  }
  if (diagnoseAutoDeductionFailure(*this, TDK, Info, Ranges))
    return DAR_FailedAlreadyDiagnosed;
  return DAR_Failed;
};

SmallVector<OriginalCallArg, 4> OriginalCallArgs;

InitListExpr *InitList = dyn_cast<InitListExpr>(Init);
if (InitList) {
  // Notionally, we substitute std::initializer_list<T> for 'auto' and deduce
  // against that. Such deduction only succeeds if removing cv-qualifiers and
  // references results in std::initializer_list<T>.
  if (!Type.getType().getNonReferenceType()->getAs<AutoType>())
    return DAR_Failed;

  // Resolving a core issue: a braced-init-list containing any designators is
  // a non-deduced context.
  for (Expr *E : InitList->inits())
    if (isa<DesignatedInitExpr>(E))
      return DAR_Failed;

  SourceRange DeducedFromInitRange;
  for (unsigned i = 0, e = InitList->getNumInits(); i < e; ++i) {
    Expr *Init = InitList->getInit(i);

    if (auto TDK = DeduceTemplateArgumentsFromCallArgument(
            *this, TemplateParamsSt.get(), 0, TemplArg, Init,
            Info, Deduced, OriginalCallArgs, /*Decomposed*/ true,
            /*ArgIdx*/ 0, /*TDF*/ 0))
      return DeductionFailed(TDK, {DeducedFromInitRange,
                                   Init->getSourceRange()});

    if (DeducedFromInitRange.isInvalid() &&
        Deduced[0].getKind() != TemplateArgument::Null)
      DeducedFromInitRange = Init->getSourceRange();
  }
} else {
  if (!getLangOpts().CPlusPlus && Init->refersToBitField()) {
    Diag(Loc, diag::err_auto_bitfield);
    return DAR_FailedAlreadyDiagnosed;
  }

  if (auto TDK = DeduceTemplateArgumentsFromCallArgument(
          *this, TemplateParamsSt.get(), 0, FuncParam, Init, Info, Deduced,
          OriginalCallArgs, /*Decomposed*/ false, /*ArgIdx*/ 0, /*TDF*/ 0))
    return DeductionFailed(TDK, {});
}

// Could be null if somehow 'auto' appears in a non-deduced context.
if (Deduced[0].getKind() != TemplateArgument::Type)
  return DeductionFailed(TDK_Incomplete, {});

QualType DeducedType = Deduced[0].getAsType();

if (InitList) {
  DeducedType = BuildStdInitializerList(DeducedType, Loc);
  if (DeducedType.isNull())
    return DAR_FailedAlreadyDiagnosed;
}

if (const auto *AT = Type.getType()->getAs<AutoType>()) {
  if (AT->isConstrained() && !IgnoreConstraints) {
    auto ConstraintsResult =
        CheckDeducedPlaceholderConstraints(*this, *AT,
                                           Type.getContainedAutoTypeLoc(),
                                           DeducedType);
    if (ConstraintsResult != DAR_Succeeded)
      return ConstraintsResult;
  }
}

Result = SubstituteDeducedTypeTransform(*this, DeducedType).Apply(Type);
if (Result.isNull())
  return DAR_FailedAlreadyDiagnosed;

// Check that the deduced argument type is compatible with the original
// argument type per C++ [temp.deduct.call]p4.
QualType DeducedA = InitList ? Deduced[0].getAsType() : Result;
for (const OriginalCallArg &OriginalArg : OriginalCallArgs) {
  assert((bool)InitList == OriginalArg.DecomposedParam &&((void)0)
         "decomposed non-init-list in auto deduction?")((void)0);
  if (auto TDK =
          CheckOriginalCallArgDeduction(*this, Info, OriginalArg, DeducedA)) {
    Result = QualType();
    return DeductionFailed(TDK, {});
  }
}

return DAR_Succeeded;
4929}

4931QualType Sema::SubstAutoType(QualType TypeWithAuto,
                           QualType TypeToReplaceAuto) {
if (TypeToReplaceAuto->isDependentType())
  return SubstituteDeducedTypeTransform(
             *this, DependentAuto{
                        TypeToReplaceAuto->containsUnexpandedParameterPack()})
      .TransformType(TypeWithAuto);
return SubstituteDeducedTypeTransform(*this, TypeToReplaceAuto)
    .TransformType(TypeWithAuto);
4940}

4942TypeSourceInfo *Sema::SubstAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                            QualType TypeToReplaceAuto) {
if (TypeToReplaceAuto->isDependentType())
  return SubstituteDeducedTypeTransform(
             *this,
             DependentAuto{
                 TypeToReplaceAuto->containsUnexpandedParameterPack()})
      .TransformType(TypeWithAuto);
return SubstituteDeducedTypeTransform(*this, TypeToReplaceAuto)
    .TransformType(TypeWithAuto);
4952}

4954QualType Sema::ReplaceAutoType(QualType TypeWithAuto,
                             QualType TypeToReplaceAuto) {
return SubstituteDeducedTypeTransform(*this, TypeToReplaceAuto,
                                      /*UseTypeSugar*/ false)
    .TransformType(TypeWithAuto);
4959}

4961TypeSourceInfo *Sema::ReplaceAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                              QualType TypeToReplaceAuto) {
return SubstituteDeducedTypeTransform(*this, TypeToReplaceAuto,
                                      /*UseTypeSugar*/ false)
    .TransformType(TypeWithAuto);
4966}

4968void Sema::DiagnoseAutoDeductionFailure(VarDecl *VDecl, Expr *Init) {
if (isa<InitListExpr>(Init))
  Diag(VDecl->getLocation(),
       VDecl->isInitCapture()
           ? diag::err_init_capture_deduction_failure_from_init_list
           : diag::err_auto_var_deduction_failure_from_init_list)
    << VDecl->getDeclName() << VDecl->getType() << Init->getSourceRange();
else
  Diag(VDecl->getLocation(),
       VDecl->isInitCapture() ? diag::err_init_capture_deduction_failure
                              : diag::err_auto_var_deduction_failure)
    << VDecl->getDeclName() << VDecl->getType() << Init->getType()
    << Init->getSourceRange();
4981}

4983bool Sema::DeduceReturnType(FunctionDecl *FD, SourceLocation Loc,
                          bool Diagnose) {
assert(FD->getReturnType()->isUndeducedType())((void)0);

// For a lambda's conversion operator, deduce any 'auto' or 'decltype(auto)'
// within the return type from the call operator's type.
if (isLambdaConversionOperator(FD)) {
  CXXRecordDecl *Lambda = cast<CXXMethodDecl>(FD)->getParent();
  FunctionDecl *CallOp = Lambda->getLambdaCallOperator();

  // For a generic lambda, instantiate the call operator if needed.
  if (auto *Args = FD->getTemplateSpecializationArgs()) {
    CallOp = InstantiateFunctionDeclaration(
        CallOp->getDescribedFunctionTemplate(), Args, Loc);
    if (!CallOp || CallOp->isInvalidDecl())
      return true;

    // We might need to deduce the return type by instantiating the definition
    // of the operator() function.
    if (CallOp->getReturnType()->isUndeducedType()) {
      runWithSufficientStackSpace(Loc, [&] {
        InstantiateFunctionDefinition(Loc, CallOp);
      });
    }
  }

  if (CallOp->isInvalidDecl())
    return true;
  assert(!CallOp->getReturnType()->isUndeducedType() &&((void)0)
         "failed to deduce lambda return type")((void)0);

  // Build the new return type from scratch.
  CallingConv RetTyCC = FD->getReturnType()
                            ->getPointeeType()
                            ->castAs<FunctionType>()
                            ->getCallConv();
  QualType RetType = getLambdaConversionFunctionResultType(
      CallOp->getType()->castAs<FunctionProtoType>(), RetTyCC);
  if (FD->getReturnType()->getAs<PointerType>())
    RetType = Context.getPointerType(RetType);
  else {
    assert(FD->getReturnType()->getAs<BlockPointerType>())((void)0);
    RetType = Context.getBlockPointerType(RetType);
  }
  Context.adjustDeducedFunctionResultType(FD, RetType);
  return false;
}

if (FD->getTemplateInstantiationPattern()) {
  runWithSufficientStackSpace(Loc, [&] {
    InstantiateFunctionDefinition(Loc, FD);
  });
}

bool StillUndeduced = FD->getReturnType()->isUndeducedType();
if (StillUndeduced && Diagnose && !FD->isInvalidDecl()) {
  Diag(Loc, diag::err_auto_fn_used_before_defined) << FD;
  Diag(FD->getLocation(), diag::note_callee_decl) << FD;
}

return StillUndeduced;
5044}

5046/// If this is a non-static member function,
5047static void
5048AddImplicitObjectParameterType(ASTContext &Context,
                             CXXMethodDecl *Method,
                             SmallVectorImpl<QualType> &ArgTypes) {
// C++11 [temp.func.order]p3:
//   [...] The new parameter is of type "reference to cv A," where cv are
//   the cv-qualifiers of the function template (if any) and A is
//   the class of which the function template is a member.
//
// The standard doesn't say explicitly, but we pick the appropriate kind of
// reference type based on [over.match.funcs]p4.
QualType ArgTy = Context.getTypeDeclType(Method->getParent());
ArgTy = Context.getQualifiedType(ArgTy, Method->getMethodQualifiers());
if (Method->getRefQualifier() == RQ_RValue)
  ArgTy = Context.getRValueReferenceType(ArgTy);
else
  ArgTy = Context.getLValueReferenceType(ArgTy);
ArgTypes.push_back(ArgTy);
5065}

5067/// Determine whether the function template \p FT1 is at least as
5068/// specialized as \p FT2.
5069static bool isAtLeastAsSpecializedAs(Sema &S,
                                   SourceLocation Loc,
                                   FunctionTemplateDecl *FT1,
                                   FunctionTemplateDecl *FT2,
                                   TemplatePartialOrderingContext TPOC,
                                   unsigned NumCallArguments1,
                                   bool Reversed) {
assert(!Reversed || TPOC == TPOC_Call)((void)0);

FunctionDecl *FD1 = FT1->getTemplatedDecl();
FunctionDecl *FD2 = FT2->getTemplatedDecl();
const FunctionProtoType *Proto1 = FD1->getType()->getAs<FunctionProtoType>();
const FunctionProtoType *Proto2 = FD2->getType()->getAs<FunctionProtoType>();

assert(Proto1 && Proto2 && "Function templates must have prototypes")((void)0);
TemplateParameterList *TemplateParams = FT2->getTemplateParameters();
SmallVector<DeducedTemplateArgument, 4> Deduced;
Deduced.resize(TemplateParams->size());

// C++0x [temp.deduct.partial]p3:
//   The types used to determine the ordering depend on the context in which
//   the partial ordering is done:
TemplateDeductionInfo Info(Loc);
SmallVector<QualType, 4> Args2;
switch (TPOC) {
case TPOC_Call: {
  //   - In the context of a function call, the function parameter types are
  //     used.
  CXXMethodDecl *Method1 = dyn_cast<CXXMethodDecl>(FD1);
  CXXMethodDecl *Method2 = dyn_cast<CXXMethodDecl>(FD2);

  // C++11 [temp.func.order]p3:
  //   [...] If only one of the function templates is a non-static
  //   member, that function template is considered to have a new
  //   first parameter inserted in its function parameter list. The
  //   new parameter is of type "reference to cv A," where cv are
  //   the cv-qualifiers of the function template (if any) and A is
  //   the class of which the function template is a member.
  //
  // Note that we interpret this to mean "if one of the function
  // templates is a non-static member and the other is a non-member";
  // otherwise, the ordering rules for static functions against non-static
  // functions don't make any sense.
  //
  // C++98/03 doesn't have this provision but we've extended DR532 to cover
  // it as wording was broken prior to it.
  SmallVector<QualType, 4> Args1;

  unsigned NumComparedArguments = NumCallArguments1;

  if (!Method2 && Method1 && !Method1->isStatic()) {
    // Compare 'this' from Method1 against first parameter from Method2.
    AddImplicitObjectParameterType(S.Context, Method1, Args1);
    ++NumComparedArguments;
  } else if (!Method1 && Method2 && !Method2->isStatic()) {
    // Compare 'this' from Method2 against first parameter from Method1.
    AddImplicitObjectParameterType(S.Context, Method2, Args2);
  } else if (Method1 && Method2 && Reversed) {
    // Compare 'this' from Method1 against second parameter from Method2
    // and 'this' from Method2 against second parameter from Method1.
    AddImplicitObjectParameterType(S.Context, Method1, Args1);
    AddImplicitObjectParameterType(S.Context, Method2, Args2);
    ++NumComparedArguments;
  }

  Args1.insert(Args1.end(), Proto1->param_type_begin(),
               Proto1->param_type_end());
  Args2.insert(Args2.end(), Proto2->param_type_begin(),
               Proto2->param_type_end());

  // C++ [temp.func.order]p5:
  //   The presence of unused ellipsis and default arguments has no effect on
  //   the partial ordering of function templates.
  if (Args1.size() > NumComparedArguments)
    Args1.resize(NumComparedArguments);
  if (Args2.size() > NumComparedArguments)
    Args2.resize(NumComparedArguments);
  if (Reversed)
    std::reverse(Args2.begin(), Args2.end());
  if (DeduceTemplateArguments(S, TemplateParams, Args2.data(), Args2.size(),
                              Args1.data(), Args1.size(), Info, Deduced,
                              TDF_None, /*PartialOrdering=*/true))
    return false;

  break;
}

case TPOC_Conversion:
  //   - In the context of a call to a conversion operator, the return types
  //     of the conversion function templates are used.
  if (DeduceTemplateArgumentsByTypeMatch(
          S, TemplateParams, Proto2->getReturnType(), Proto1->getReturnType(),
          Info, Deduced, TDF_None,
          /*PartialOrdering=*/true))
    return false;
  break;

case TPOC_Other:
  //   - In other contexts (14.6.6.2) the function template's function type
  //     is used.
  if (DeduceTemplateArgumentsByTypeMatch(S, TemplateParams,
                                         FD2->getType(), FD1->getType(),
                                         Info, Deduced, TDF_None,
                                         /*PartialOrdering=*/true))
    return false;
  break;
}

// C++0x [temp.deduct.partial]p11:
//   In most cases, all template parameters must have values in order for
//   deduction to succeed, but for partial ordering purposes a template
//   parameter may remain without a value provided it is not used in the
//   types being used for partial ordering. [ Note: a template parameter used
//   in a non-deduced context is considered used. -end note]
unsigned ArgIdx = 0, NumArgs = Deduced.size();
for (; ArgIdx != NumArgs; ++ArgIdx)
  if (Deduced[ArgIdx].isNull())
    break;

// FIXME: We fail to implement [temp.deduct.type]p1 along this path. We need
// to substitute the deduced arguments back into the template and check that
// we get the right type.

if (ArgIdx == NumArgs) {
  // All template arguments were deduced. FT1 is at least as specialized
  // as FT2.
  return true;
}

// Figure out which template parameters were used.
llvm::SmallBitVector UsedParameters(TemplateParams->size());
switch (TPOC) {
case TPOC_Call:
  for (unsigned I = 0, N = Args2.size(); I != N; ++I)
    ::MarkUsedTemplateParameters(S.Context, Args2[I], false,
                                 TemplateParams->getDepth(),
                                 UsedParameters);
  break;

case TPOC_Conversion:
  ::MarkUsedTemplateParameters(S.Context, Proto2->getReturnType(), false,
                               TemplateParams->getDepth(), UsedParameters);
  break;

case TPOC_Other:
  ::MarkUsedTemplateParameters(S.Context, FD2->getType(), false,
                               TemplateParams->getDepth(),
                               UsedParameters);
  break;
}

for (; ArgIdx != NumArgs; ++ArgIdx)
  // If this argument had no value deduced but was used in one of the types
  // used for partial ordering, then deduction fails.
  if (Deduced[ArgIdx].isNull() && UsedParameters[ArgIdx])
    return false;

return true;
5227}

5229/// Determine whether this a function template whose parameter-type-list
5230/// ends with a function parameter pack.
5231static bool isVariadicFunctionTemplate(FunctionTemplateDecl *FunTmpl) {
FunctionDecl *Function = FunTmpl->getTemplatedDecl();
unsigned NumParams = Function->getNumParams();
if (NumParams == 0)
  return false;

ParmVarDecl *Last = Function->getParamDecl(NumParams - 1);
if (!Last->isParameterPack())
  return false;

// Make sure that no previous parameter is a parameter pack.
while (--NumParams > 0) {
  if (Function->getParamDecl(NumParams - 1)->isParameterPack())
    return false;
}

return true;
5248}

5250/// Returns the more specialized function template according
5251/// to the rules of function template partial ordering (C++ [temp.func.order]).
5252///
5253/// \param FT1 the first function template
5254///
5255/// \param FT2 the second function template
5256///
5257/// \param TPOC the context in which we are performing partial ordering of
5258/// function templates.
5259///
5260/// \param NumCallArguments1 The number of arguments in the call to FT1, used
5261/// only when \c TPOC is \c TPOC_Call.
5262///
5263/// \param NumCallArguments2 The number of arguments in the call to FT2, used
5264/// only when \c TPOC is \c TPOC_Call.
5265///
5266/// \param Reversed If \c true, exactly one of FT1 and FT2 is an overload
5267/// candidate with a reversed parameter order. In this case, the corresponding
5268/// P/A pairs between FT1 and FT2 are reversed.
5269///
5270/// \returns the more specialized function template. If neither
5271/// template is more specialized, returns NULL.
5272FunctionTemplateDecl *
5273Sema::getMoreSpecializedTemplate(FunctionTemplateDecl *FT1,
                               FunctionTemplateDecl *FT2,
                               SourceLocation Loc,
                               TemplatePartialOrderingContext TPOC,
                               unsigned NumCallArguments1,
                               unsigned NumCallArguments2,
                               bool Reversed) {

auto JudgeByConstraints = [&] () -> FunctionTemplateDecl * {
  llvm::SmallVector<const Expr *, 3> AC1, AC2;
  FT1->getAssociatedConstraints(AC1);
  FT2->getAssociatedConstraints(AC2);
  bool AtLeastAsConstrained1, AtLeastAsConstrained2;
  if (IsAtLeastAsConstrained(FT1, AC1, FT2, AC2, AtLeastAsConstrained1))
    return nullptr;
  if (IsAtLeastAsConstrained(FT2, AC2, FT1, AC1, AtLeastAsConstrained2))
    return nullptr;
  if (AtLeastAsConstrained1 == AtLeastAsConstrained2)
    return nullptr;
  return AtLeastAsConstrained1 ? FT1 : FT2;
};

bool Better1 = isAtLeastAsSpecializedAs(*this, Loc, FT1, FT2, TPOC,
                                        NumCallArguments1, Reversed);
bool Better2 = isAtLeastAsSpecializedAs(*this, Loc, FT2, FT1, TPOC,
                                        NumCallArguments2, Reversed);

if (Better1 != Better2) // We have a clear winner
  return Better1 ? FT1 : FT2;

if (!Better1 && !Better2) // Neither is better than the other
  return JudgeByConstraints();

// FIXME: This mimics what GCC implements, but doesn't match up with the
// proposed resolution for core issue 692. This area needs to be sorted out,
// but for now we attempt to maintain compatibility.
bool Variadic1 = isVariadicFunctionTemplate(FT1);
bool Variadic2 = isVariadicFunctionTemplate(FT2);
if (Variadic1 != Variadic2)
  return Variadic1? FT2 : FT1;

return JudgeByConstraints();
5315}

5317/// Determine if the two templates are equivalent.
5318static bool isSameTemplate(TemplateDecl *T1, TemplateDecl *T2) {
if (T1 == T2)
  return true;

if (!T1 || !T2)
  return false;

return T1->getCanonicalDecl() == T2->getCanonicalDecl();
5326}

5328/// Retrieve the most specialized of the given function template
5329/// specializations.
5330///
5331/// \param SpecBegin the start iterator of the function template
5332/// specializations that we will be comparing.
5333///
5334/// \param SpecEnd the end iterator of the function template
5335/// specializations, paired with \p SpecBegin.
5336///
5337/// \param Loc the location where the ambiguity or no-specializations
5338/// diagnostic should occur.
5339///
5340/// \param NoneDiag partial diagnostic used to diagnose cases where there are
5341/// no matching candidates.
5342///
5343/// \param AmbigDiag partial diagnostic used to diagnose an ambiguity, if one
5344/// occurs.
5345///
5346/// \param CandidateDiag partial diagnostic used for each function template
5347/// specialization that is a candidate in the ambiguous ordering. One parameter
5348/// in this diagnostic should be unbound, which will correspond to the string
5349/// describing the template arguments for the function template specialization.
5350///
5351/// \returns the most specialized function template specialization, if
5352/// found. Otherwise, returns SpecEnd.
5353UnresolvedSetIterator Sema::getMostSpecialized(
  UnresolvedSetIterator SpecBegin, UnresolvedSetIterator SpecEnd,
  TemplateSpecCandidateSet &FailedCandidates,
  SourceLocation Loc, const PartialDiagnostic &NoneDiag,
  const PartialDiagnostic &AmbigDiag, const PartialDiagnostic &CandidateDiag,
  bool Complain, QualType TargetType) {
if (SpecBegin == SpecEnd) {
  if (Complain) {
    Diag(Loc, NoneDiag);
    FailedCandidates.NoteCandidates(*this, Loc);
  }
  return SpecEnd;
}

if (SpecBegin + 1 == SpecEnd)
  return SpecBegin;

// Find the function template that is better than all of the templates it
// has been compared to.
UnresolvedSetIterator Best = SpecBegin;
FunctionTemplateDecl *BestTemplate
  = cast<FunctionDecl>(*Best)->getPrimaryTemplate();
assert(BestTemplate && "Not a function template specialization?")((void)0);
for (UnresolvedSetIterator I = SpecBegin + 1; I != SpecEnd; ++I) {
  FunctionTemplateDecl *Challenger
    = cast<FunctionDecl>(*I)->getPrimaryTemplate();
  assert(Challenger && "Not a function template specialization?")((void)0);
  if (isSameTemplate(getMoreSpecializedTemplate(BestTemplate, Challenger,
                                                Loc, TPOC_Other, 0, 0),
                     Challenger)) {
    Best = I;
    BestTemplate = Challenger;
  }
}

// Make sure that the "best" function template is more specialized than all
// of the others.
bool Ambiguous = false;
for (UnresolvedSetIterator I = SpecBegin; I != SpecEnd; ++I) {
  FunctionTemplateDecl *Challenger
    = cast<FunctionDecl>(*I)->getPrimaryTemplate();
  if (I != Best &&
      !isSameTemplate(getMoreSpecializedTemplate(BestTemplate, Challenger,
                                                 Loc, TPOC_Other, 0, 0),
                      BestTemplate)) {
    Ambiguous = true;
    break;
  }
}

if (!Ambiguous) {
  // We found an answer. Return it.
  return Best;
}

// Diagnose the ambiguity.
if (Complain) {
  Diag(Loc, AmbigDiag);

  // FIXME: Can we order the candidates in some sane way?
  for (UnresolvedSetIterator I = SpecBegin; I != SpecEnd; ++I) {
    PartialDiagnostic PD = CandidateDiag;
    const auto *FD = cast<FunctionDecl>(*I);
    PD << FD << getTemplateArgumentBindingsText(
                    FD->getPrimaryTemplate()->getTemplateParameters(),
                    *FD->getTemplateSpecializationArgs());
    if (!TargetType.isNull())
      HandleFunctionTypeMismatch(PD, FD->getType(), TargetType);
    Diag((*I)->getLocation(), PD);
  }
}

return SpecEnd;
5426}

5428/// Determine whether one partial specialization, P1, is at least as
5429/// specialized than another, P2.
5430///
5431/// \tparam TemplateLikeDecl The kind of P2, which must be a
5432/// TemplateDecl or {Class,Var}TemplatePartialSpecializationDecl.
5433/// \param T1 The injected-class-name of P1 (faked for a variable template).
5434/// \param T2 The injected-class-name of P2 (faked for a variable template).
5435template<typename TemplateLikeDecl>
5436static bool isAtLeastAsSpecializedAs(Sema &S, QualType T1, QualType T2,
                                   TemplateLikeDecl *P2,
                                   TemplateDeductionInfo &Info) {
// C++ [temp.class.order]p1:
//   For two class template partial specializations, the first is at least as
//   specialized as the second if, given the following rewrite to two
//   function templates, the first function template is at least as
//   specialized as the second according to the ordering rules for function
//   templates (14.6.6.2):
//     - the first function template has the same template parameters as the
//       first partial specialization and has a single function parameter
//       whose type is a class template specialization with the template
//       arguments of the first partial specialization, and
//     - the second function template has the same template parameters as the
//       second partial specialization and has a single function parameter
//       whose type is a class template specialization with the template
//       arguments of the second partial specialization.
//
// Rather than synthesize function templates, we merely perform the
// equivalent partial ordering by performing deduction directly on
// the template arguments of the class template partial
// specializations. This computation is slightly simpler than the
// general problem of function template partial ordering, because
// class template partial specializations are more constrained. We
// know that every template parameter is deducible from the class
// template partial specialization's template arguments, for
// example.
SmallVector<DeducedTemplateArgument, 4> Deduced;

// Determine whether P1 is at least as specialized as P2.
Deduced.resize(P2->getTemplateParameters()->size());
if (DeduceTemplateArgumentsByTypeMatch(S, P2->getTemplateParameters(),
                                       T2, T1, Info, Deduced, TDF_None,
                                       /*PartialOrdering=*/true))
  return false;

SmallVector<TemplateArgument, 4> DeducedArgs(Deduced.begin(),
                                             Deduced.end());
Sema::InstantiatingTemplate Inst(S, Info.getLocation(), P2, DeducedArgs,
                                 Info);
if (Inst.isInvalid())
  return false;

auto *TST1 = T1->castAs<TemplateSpecializationType>();
bool AtLeastAsSpecialized;
S.runWithSufficientStackSpace(Info.getLocation(), [&] {
  AtLeastAsSpecialized = !FinishTemplateArgumentDeduction(
      S, P2, /*IsPartialOrdering=*/true,
      TemplateArgumentList(TemplateArgumentList::OnStack,
                           TST1->template_arguments()),
      Deduced, Info);
});
return AtLeastAsSpecialized;
5489}

5491/// Returns the more specialized class template partial specialization
5492/// according to the rules of partial ordering of class template partial
5493/// specializations (C++ [temp.class.order]).
5494///
5495/// \param PS1 the first class template partial specialization
5496///
5497/// \param PS2 the second class template partial specialization
5498///
5499/// \returns the more specialized class template partial specialization. If
5500/// neither partial specialization is more specialized, returns NULL.
5501ClassTemplatePartialSpecializationDecl *
5502Sema::getMoreSpecializedPartialSpecialization(
                                ClassTemplatePartialSpecializationDecl *PS1,
                                ClassTemplatePartialSpecializationDecl *PS2,
                                            SourceLocation Loc) {
QualType PT1 = PS1->getInjectedSpecializationType();
QualType PT2 = PS2->getInjectedSpecializationType();

TemplateDeductionInfo Info(Loc);
bool Better1 = isAtLeastAsSpecializedAs(*this, PT1, PT2, PS2, Info);
bool Better2 = isAtLeastAsSpecializedAs(*this, PT2, PT1, PS1, Info);

if (!Better1 && !Better2)
    return nullptr;
if (Better1 && Better2) {
  llvm::SmallVector<const Expr *, 3> AC1, AC2;
  PS1->getAssociatedConstraints(AC1);
  PS2->getAssociatedConstraints(AC2);
  bool AtLeastAsConstrained1, AtLeastAsConstrained2;
  if (IsAtLeastAsConstrained(PS1, AC1, PS2, AC2, AtLeastAsConstrained1))
    return nullptr;
  if (IsAtLeastAsConstrained(PS2, AC2, PS1, AC1, AtLeastAsConstrained2))
    return nullptr;
  if (AtLeastAsConstrained1 == AtLeastAsConstrained2)
    return nullptr;
  return AtLeastAsConstrained1 ? PS1 : PS2;
}

return Better1 ? PS1 : PS2;
5530}

5532bool Sema::isMoreSpecializedThanPrimary(
  ClassTemplatePartialSpecializationDecl *Spec, TemplateDeductionInfo &Info) {
ClassTemplateDecl *Primary = Spec->getSpecializedTemplate();
QualType PrimaryT = Primary->getInjectedClassNameSpecialization();
QualType PartialT = Spec->getInjectedSpecializationType();
if (!isAtLeastAsSpecializedAs(*this, PartialT, PrimaryT, Primary, Info))
  return false;
if (!isAtLeastAsSpecializedAs(*this, PrimaryT, PartialT, Spec, Info))
  return true;
Info.clearSFINAEDiagnostic();
llvm::SmallVector<const Expr *, 3> PrimaryAC, SpecAC;
Primary->getAssociatedConstraints(PrimaryAC);
Spec->getAssociatedConstraints(SpecAC);
bool AtLeastAsConstrainedPrimary, AtLeastAsConstrainedSpec;
if (IsAtLeastAsConstrained(Spec, SpecAC, Primary, PrimaryAC,
                           AtLeastAsConstrainedSpec))
  return false;
if (!AtLeastAsConstrainedSpec)
  return false;
if (IsAtLeastAsConstrained(Primary, PrimaryAC, Spec, SpecAC,
                           AtLeastAsConstrainedPrimary))
  return false;
return !AtLeastAsConstrainedPrimary;
5555}

5557VarTemplatePartialSpecializationDecl *
5558Sema::getMoreSpecializedPartialSpecialization(
  VarTemplatePartialSpecializationDecl *PS1,
  VarTemplatePartialSpecializationDecl *PS2, SourceLocation Loc) {
// Pretend the variable template specializations are class template
// specializations and form a fake injected class name type for comparison.
assert(PS1->getSpecializedTemplate() == PS2->getSpecializedTemplate() &&((void)0)
       "the partial specializations being compared should specialize"((void)0)
       " the same template.")((void)0);
TemplateName Name(PS1->getSpecializedTemplate());
TemplateName CanonTemplate = Context.getCanonicalTemplateName(Name);
QualType PT1 = Context.getTemplateSpecializationType(
    CanonTemplate, PS1->getTemplateArgs().asArray());
QualType PT2 = Context.getTemplateSpecializationType(
    CanonTemplate, PS2->getTemplateArgs().asArray());

TemplateDeductionInfo Info(Loc);
bool Better1 = isAtLeastAsSpecializedAs(*this, PT1, PT2, PS2, Info);
bool Better2 = isAtLeastAsSpecializedAs(*this, PT2, PT1, PS1, Info);

if (!Better1 && !Better2)
  return nullptr;
if (Better1 && Better2) {
  llvm::SmallVector<const Expr *, 3> AC1, AC2;
  PS1->getAssociatedConstraints(AC1);
  PS2->getAssociatedConstraints(AC2);
  bool AtLeastAsConstrained1, AtLeastAsConstrained2;
  if (IsAtLeastAsConstrained(PS1, AC1, PS2, AC2, AtLeastAsConstrained1))
    return nullptr;
  if (IsAtLeastAsConstrained(PS2, AC2, PS1, AC1, AtLeastAsConstrained2))
    return nullptr;
  if (AtLeastAsConstrained1 == AtLeastAsConstrained2)
    return nullptr;
  return AtLeastAsConstrained1 ? PS1 : PS2;
}

return Better1 ? PS1 : PS2;
5594}

5596bool Sema::isMoreSpecializedThanPrimary(
  VarTemplatePartialSpecializationDecl *Spec, TemplateDeductionInfo &Info) {
TemplateDecl *Primary = Spec->getSpecializedTemplate();
// FIXME: Cache the injected template arguments rather than recomputing
// them for each partial specialization.
SmallVector<TemplateArgument, 8> PrimaryArgs;
Context.getInjectedTemplateArgs(Primary->getTemplateParameters(),
                                PrimaryArgs);

TemplateName CanonTemplate =
    Context.getCanonicalTemplateName(TemplateName(Primary));
QualType PrimaryT = Context.getTemplateSpecializationType(
    CanonTemplate, PrimaryArgs);
QualType PartialT = Context.getTemplateSpecializationType(
    CanonTemplate, Spec->getTemplateArgs().asArray());

if (!isAtLeastAsSpecializedAs(*this, PartialT, PrimaryT, Primary, Info))
  return false;
if (!isAtLeastAsSpecializedAs(*this, PrimaryT, PartialT, Spec, Info))
  return true;
Info.clearSFINAEDiagnostic();
llvm::SmallVector<const Expr *, 3> PrimaryAC, SpecAC;
Primary->getAssociatedConstraints(PrimaryAC);
Spec->getAssociatedConstraints(SpecAC);
bool AtLeastAsConstrainedPrimary, AtLeastAsConstrainedSpec;
if (IsAtLeastAsConstrained(Spec, SpecAC, Primary, PrimaryAC,
                           AtLeastAsConstrainedSpec))
  return false;
if (!AtLeastAsConstrainedSpec)
  return false;
if (IsAtLeastAsConstrained(Primary, PrimaryAC, Spec, SpecAC,
                           AtLeastAsConstrainedPrimary))
  return false;
return !AtLeastAsConstrainedPrimary;
5630}

5632bool Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs(
   TemplateParameterList *P, TemplateDecl *AArg, SourceLocation Loc) {
// C++1z [temp.arg.template]p4: (DR 150)
//   A template template-parameter P is at least as specialized as a
//   template template-argument A if, given the following rewrite to two
//   function templates...

// Rather than synthesize function templates, we merely perform the
// equivalent partial ordering by performing deduction directly on
// the template parameter lists of the template template parameters.
//
//   Given an invented class template X with the template parameter list of
//   A (including default arguments):
TemplateName X = Context.getCanonicalTemplateName(TemplateName(AArg));
TemplateParameterList *A = AArg->getTemplateParameters();

//    - Each function template has a single function parameter whose type is
//      a specialization of X with template arguments corresponding to the
//      template parameters from the respective function template
SmallVector<TemplateArgument, 8> AArgs;
Context.getInjectedTemplateArgs(A, AArgs);

// Check P's arguments against A's parameter list. This will fill in default
// template arguments as needed. AArgs are already correct by construction.
// We can't just use CheckTemplateIdType because that will expand alias
// templates.
SmallVector<TemplateArgument, 4> PArgs;
{
  SFINAETrap Trap(*this);

  Context.getInjectedTemplateArgs(P, PArgs);
  TemplateArgumentListInfo PArgList(P->getLAngleLoc(),
                                    P->getRAngleLoc());
  for (unsigned I = 0, N = P->size(); I != N; ++I) {
    // Unwrap packs that getInjectedTemplateArgs wrapped around pack
    // expansions, to form an "as written" argument list.
    TemplateArgument Arg = PArgs[I];
    if (Arg.getKind() == TemplateArgument::Pack) {
      assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion())((void)0);
      Arg = *Arg.pack_begin();
    }
    PArgList.addArgument(getTrivialTemplateArgumentLoc(
        Arg, QualType(), P->getParam(I)->getLocation()));
  }
  PArgs.clear();

  // C++1z [temp.arg.template]p3:
  //   If the rewrite produces an invalid type, then P is not at least as
  //   specialized as A.
  if (CheckTemplateArgumentList(AArg, Loc, PArgList, false, PArgs) ||
      Trap.hasErrorOccurred())
    return false;
}

QualType AType = Context.getTemplateSpecializationType(X, AArgs);
QualType PType = Context.getTemplateSpecializationType(X, PArgs);

//   ... the function template corresponding to P is at least as specialized
//   as the function template corresponding to A according to the partial
//   ordering rules for function templates.
TemplateDeductionInfo Info(Loc, A->getDepth());
return isAtLeastAsSpecializedAs(*this, PType, AType, AArg, Info);
5694}

5696namespace {
5697struct MarkUsedTemplateParameterVisitor :
  RecursiveASTVisitor<MarkUsedTemplateParameterVisitor> {
llvm::SmallBitVector &Used;
unsigned Depth;

MarkUsedTemplateParameterVisitor(llvm::SmallBitVector &Used,
                                 unsigned Depth)
    : Used(Used), Depth(Depth) { }

bool VisitTemplateTypeParmType(TemplateTypeParmType *T) {
  if (T->getDepth() == Depth)
    Used[T->getIndex()] = true;
  return true;
}

bool TraverseTemplateName(TemplateName Template) {
  if (auto *TTP =
          dyn_cast<TemplateTemplateParmDecl>(Template.getAsTemplateDecl()))
    if (TTP->getDepth() == Depth)
      Used[TTP->getIndex()] = true;
  RecursiveASTVisitor<MarkUsedTemplateParameterVisitor>::
      TraverseTemplateName(Template);
  return true;
}

bool VisitDeclRefExpr(DeclRefExpr *E) {
  if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(E->getDecl()))
    if (NTTP->getDepth() == Depth)
      Used[NTTP->getIndex()] = true;
  return true;
}
5728};
5729}

5731/// Mark the template parameters that are used by the given
5732/// expression.
5733static void
5734MarkUsedTemplateParameters(ASTContext &Ctx,
                         const Expr *E,
                         bool OnlyDeduced,
                         unsigned Depth,
                         llvm::SmallBitVector &Used) {
if (!OnlyDeduced) {
  MarkUsedTemplateParameterVisitor(Used, Depth)
      .TraverseStmt(const_cast<Expr *>(E));
  return;
}

// We can deduce from a pack expansion.
if (const PackExpansionExpr *Expansion = dyn_cast<PackExpansionExpr>(E))
  E = Expansion->getPattern();

const NonTypeTemplateParmDecl *NTTP = getDeducedParameterFromExpr(E, Depth);
if (!NTTP)
  return;

if (NTTP->getDepth() == Depth)
  Used[NTTP->getIndex()] = true;

// In C++17 mode, additional arguments may be deduced from the type of a
// non-type argument.
if (Ctx.getLangOpts().CPlusPlus17)
  MarkUsedTemplateParameters(Ctx, NTTP->getType(), OnlyDeduced, Depth, Used);
5760}

5762/// Mark the template parameters that are used by the given
5763/// nested name specifier.
5764static void
5765MarkUsedTemplateParameters(ASTContext &Ctx,
                         NestedNameSpecifier *NNS,
                         bool OnlyDeduced,
                         unsigned Depth,
                         llvm::SmallBitVector &Used) {
if (!NNS)
  return;

MarkUsedTemplateParameters(Ctx, NNS->getPrefix(), OnlyDeduced, Depth,
                           Used);
MarkUsedTemplateParameters(Ctx, QualType(NNS->getAsType(), 0),
                           OnlyDeduced, Depth, Used);
5777}

5779/// Mark the template parameters that are used by the given
5780/// template name.
5781static void
5782MarkUsedTemplateParameters(ASTContext &Ctx,
                         TemplateName Name,
                         bool OnlyDeduced,
                         unsigned Depth,
                         llvm::SmallBitVector &Used) {
if (TemplateDecl *Template = Name.getAsTemplateDecl()) {
  if (TemplateTemplateParmDecl *TTP
        = dyn_cast<TemplateTemplateParmDecl>(Template)) {
    if (TTP->getDepth() == Depth)
      Used[TTP->getIndex()] = true;
  }
  return;
}

if (QualifiedTemplateName *QTN = Name.getAsQualifiedTemplateName())
  MarkUsedTemplateParameters(Ctx, QTN->getQualifier(), OnlyDeduced,
                             Depth, Used);
if (DependentTemplateName *DTN = Name.getAsDependentTemplateName())
  MarkUsedTemplateParameters(Ctx, DTN->getQualifier(), OnlyDeduced,
                             Depth, Used);
5802}

5804/// Mark the template parameters that are used by the given
5805/// type.
5806static void
5807MarkUsedTemplateParameters(ASTContext &Ctx, QualType T,
                         bool OnlyDeduced,
                         unsigned Depth,
                         llvm::SmallBitVector &Used) {
if (T.isNull())
  return;

// Non-dependent types have nothing deducible
if (!T->isDependentType())
  return;

T = Ctx.getCanonicalType(T);
switch (T->getTypeClass()) {
case Type::Pointer:
  MarkUsedTemplateParameters(Ctx,
                             cast<PointerType>(T)->getPointeeType(),
                             OnlyDeduced,
                             Depth,
                             Used);
  break;

case Type::BlockPointer:
  MarkUsedTemplateParameters(Ctx,
                             cast<BlockPointerType>(T)->getPointeeType(),
                             OnlyDeduced,
                             Depth,
                             Used);
  break;

case Type::LValueReference:
case Type::RValueReference:
  MarkUsedTemplateParameters(Ctx,
                             cast<ReferenceType>(T)->getPointeeType(),
                             OnlyDeduced,
                             Depth,
                             Used);
  break;

case Type::MemberPointer: {
  const MemberPointerType *MemPtr = cast<MemberPointerType>(T.getTypePtr());
  MarkUsedTemplateParameters(Ctx, MemPtr->getPointeeType(), OnlyDeduced,
                             Depth, Used);
  MarkUsedTemplateParameters(Ctx, QualType(MemPtr->getClass(), 0),
                             OnlyDeduced, Depth, Used);
  break;
}

case Type::DependentSizedArray:
  MarkUsedTemplateParameters(Ctx,
                             cast<DependentSizedArrayType>(T)->getSizeExpr(),
                             OnlyDeduced, Depth, Used);
  // Fall through to check the element type
  LLVM_FALLTHROUGH[[gnu::fallthrough]];

case Type::ConstantArray:
case Type::IncompleteArray:
  MarkUsedTemplateParameters(Ctx,
                             cast<ArrayType>(T)->getElementType(),
                             OnlyDeduced, Depth, Used);
  break;

case Type::Vector:
case Type::ExtVector:
  MarkUsedTemplateParameters(Ctx,
                             cast<VectorType>(T)->getElementType(),
                             OnlyDeduced, Depth, Used);
  break;

case Type::DependentVector: {
  const auto *VecType = cast<DependentVectorType>(T);
  MarkUsedTemplateParameters(Ctx, VecType->getElementType(), OnlyDeduced,
                             Depth, Used);
  MarkUsedTemplateParameters(Ctx, VecType->getSizeExpr(), OnlyDeduced, Depth,
                             Used);
  break;
}
case Type::DependentSizedExtVector: {
  const DependentSizedExtVectorType *VecType
    = cast<DependentSizedExtVectorType>(T);
  MarkUsedTemplateParameters(Ctx, VecType->getElementType(), OnlyDeduced,
                             Depth, Used);
  MarkUsedTemplateParameters(Ctx, VecType->getSizeExpr(), OnlyDeduced,
                             Depth, Used);
  break;
}

case Type::DependentAddressSpace: {
  const DependentAddressSpaceType *DependentASType =
      cast<DependentAddressSpaceType>(T);
  MarkUsedTemplateParameters(Ctx, DependentASType->getPointeeType(),
                             OnlyDeduced, Depth, Used);
  MarkUsedTemplateParameters(Ctx,
                             DependentASType->getAddrSpaceExpr(),
                             OnlyDeduced, Depth, Used);
  break;
}

case Type::ConstantMatrix: {
  const ConstantMatrixType *MatType = cast<ConstantMatrixType>(T);
  MarkUsedTemplateParameters(Ctx, MatType->getElementType(), OnlyDeduced,
                             Depth, Used);
  break;
}

case Type::DependentSizedMatrix: {
  const DependentSizedMatrixType *MatType = cast<DependentSizedMatrixType>(T);
  MarkUsedTemplateParameters(Ctx, MatType->getElementType(), OnlyDeduced,
                             Depth, Used);
  MarkUsedTemplateParameters(Ctx, MatType->getRowExpr(), OnlyDeduced, Depth,
                             Used);
  MarkUsedTemplateParameters(Ctx, MatType->getColumnExpr(), OnlyDeduced,
                             Depth, Used);
  break;
}

case Type::FunctionProto: {
  const FunctionProtoType *Proto = cast<FunctionProtoType>(T);
  MarkUsedTemplateParameters(Ctx, Proto->getReturnType(), OnlyDeduced, Depth,
                             Used);
  for (unsigned I = 0, N = Proto->getNumParams(); I != N; ++I) {
    // C++17 [temp.deduct.type]p5:
    //   The non-deduced contexts are: [...]
    //   -- A function parameter pack that does not occur at the end of the
    //      parameter-declaration-list.
    if (!OnlyDeduced || I + 1 == N ||
        !Proto->getParamType(I)->getAs<PackExpansionType>()) {
      MarkUsedTemplateParameters(Ctx, Proto->getParamType(I), OnlyDeduced,
                                 Depth, Used);
    } else {
      // FIXME: C++17 [temp.deduct.call]p1:
      //   When a function parameter pack appears in a non-deduced context,
      //   the type of that pack is never deduced.
      //
      // We should also track a set of "never deduced" parameters, and
      // subtract that from the list of deduced parameters after marking.
    }
  }
  if (auto *E = Proto->getNoexceptExpr())
    MarkUsedTemplateParameters(Ctx, E, OnlyDeduced, Depth, Used);
  break;
}

case Type::TemplateTypeParm: {
  const TemplateTypeParmType *TTP = cast<TemplateTypeParmType>(T);
  if (TTP->getDepth() == Depth)
    Used[TTP->getIndex()] = true;
  break;
}

case Type::SubstTemplateTypeParmPack: {
  const SubstTemplateTypeParmPackType *Subst
    = cast<SubstTemplateTypeParmPackType>(T);
  MarkUsedTemplateParameters(Ctx,
                             QualType(Subst->getReplacedParameter(), 0),
                             OnlyDeduced, Depth, Used);
  MarkUsedTemplateParameters(Ctx, Subst->getArgumentPack(),
                             OnlyDeduced, Depth, Used);
  break;
}

case Type::InjectedClassName:
  T = cast<InjectedClassNameType>(T)->getInjectedSpecializationType();
  LLVM_FALLTHROUGH[[gnu::fallthrough]];

case Type::TemplateSpecialization: {
  const TemplateSpecializationType *Spec
    = cast<TemplateSpecializationType>(T);
  MarkUsedTemplateParameters(Ctx, Spec->getTemplateName(), OnlyDeduced,
                             Depth, Used);

  // C++0x [temp.deduct.type]p9:
  //   If the template argument list of P contains a pack expansion that is
  //   not the last template argument, the entire template argument list is a
  //   non-deduced context.
  if (OnlyDeduced &&
      hasPackExpansionBeforeEnd(Spec->template_arguments()))
    break;

  for (unsigned I = 0, N = Spec->getNumArgs(); I != N; ++I)
    MarkUsedTemplateParameters(Ctx, Spec->getArg(I), OnlyDeduced, Depth,
                               Used);
  break;
}

case Type::Complex:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<ComplexType>(T)->getElementType(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::Atomic:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<AtomicType>(T)->getValueType(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::DependentName:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<DependentNameType>(T)->getQualifier(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::DependentTemplateSpecialization: {
  // C++14 [temp.deduct.type]p5:
  //   The non-deduced contexts are:
  //     -- The nested-name-specifier of a type that was specified using a
  //        qualified-id
  //
  // C++14 [temp.deduct.type]p6:
  //   When a type name is specified in a way that includes a non-deduced
  //   context, all of the types that comprise that type name are also
  //   non-deduced.
  if (OnlyDeduced)
    break;

  const DependentTemplateSpecializationType *Spec
    = cast<DependentTemplateSpecializationType>(T);

  MarkUsedTemplateParameters(Ctx, Spec->getQualifier(),
                             OnlyDeduced, Depth, Used);

  for (unsigned I = 0, N = Spec->getNumArgs(); I != N; ++I)
    MarkUsedTemplateParameters(Ctx, Spec->getArg(I), OnlyDeduced, Depth,
                               Used);
  break;
}

case Type::TypeOf:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<TypeOfType>(T)->getUnderlyingType(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::TypeOfExpr:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<TypeOfExprType>(T)->getUnderlyingExpr(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::Decltype:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<DecltypeType>(T)->getUnderlyingExpr(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::UnaryTransform:
  if (!OnlyDeduced)
    MarkUsedTemplateParameters(Ctx,
                               cast<UnaryTransformType>(T)->getUnderlyingType(),
                               OnlyDeduced, Depth, Used);
  break;

case Type::PackExpansion:
  MarkUsedTemplateParameters(Ctx,
                             cast<PackExpansionType>(T)->getPattern(),
                             OnlyDeduced, Depth, Used);
  break;

case Type::Auto:
case Type::DeducedTemplateSpecialization:
  MarkUsedTemplateParameters(Ctx,
                             cast<DeducedType>(T)->getDeducedType(),
                             OnlyDeduced, Depth, Used);
  break;
case Type::DependentExtInt:
  MarkUsedTemplateParameters(Ctx,
                             cast<DependentExtIntType>(T)->getNumBitsExpr(),
                             OnlyDeduced, Depth, Used);
  break;

// None of these types have any template parameters in them.
case Type::Builtin:
case Type::VariableArray:
case Type::FunctionNoProto:
case Type::Record:
case Type::Enum:
case Type::ObjCInterface:
case Type::ObjCObject:
case Type::ObjCObjectPointer:
case Type::UnresolvedUsing:
case Type::Pipe:
case Type::ExtInt:
6095#define TYPE(Class, Base)
6096#define ABSTRACT_TYPE(Class, Base)
6097#define DEPENDENT_TYPE(Class, Base)
6098#define NON_CANONICAL_TYPE(Class, Base) case Type::Class:
6099#include "clang/AST/TypeNodes.inc"
  break;
}
6102}

6104/// Mark the template parameters that are used by this
6105/// template argument.
6106static void
6107MarkUsedTemplateParameters(ASTContext &Ctx,
                         const TemplateArgument &TemplateArg,
                         bool OnlyDeduced,
                         unsigned Depth,
                         llvm::SmallBitVector &Used) {
switch (TemplateArg.getKind()) {
case TemplateArgument::Null:
case TemplateArgument::Integral:
case TemplateArgument::Declaration:
  break;

case TemplateArgument::NullPtr:
  MarkUsedTemplateParameters(Ctx, TemplateArg.getNullPtrType(), OnlyDeduced,
                             Depth, Used);
  break;

case TemplateArgument::Type:
  MarkUsedTemplateParameters(Ctx, TemplateArg.getAsType(), OnlyDeduced,
                             Depth, Used);
  break;

case TemplateArgument::Template:
case TemplateArgument::TemplateExpansion:
  MarkUsedTemplateParameters(Ctx,
                             TemplateArg.getAsTemplateOrTemplatePattern(),
                             OnlyDeduced, Depth, Used);
  break;

case TemplateArgument::Expression:
  MarkUsedTemplateParameters(Ctx, TemplateArg.getAsExpr(), OnlyDeduced,
                             Depth, Used);
  break;

case TemplateArgument::Pack:
  for (const auto &P : TemplateArg.pack_elements())
    MarkUsedTemplateParameters(Ctx, P, OnlyDeduced, Depth, Used);
  break;
}
6145}

6147/// Mark which template parameters are used in a given expression.
6148///
6149/// \param E the expression from which template parameters will be deduced.
6150///
6151/// \param Used a bit vector whose elements will be set to \c true
6152/// to indicate when the corresponding template parameter will be
6153/// deduced.
6154void
6155Sema::MarkUsedTemplateParameters(const Expr *E, bool OnlyDeduced,
                               unsigned Depth,
                               llvm::SmallBitVector &Used) {
::MarkUsedTemplateParameters(Context, E, OnlyDeduced, Depth, Used);
6159}

6161/// Mark which template parameters can be deduced from a given
6162/// template argument list.
6163///
6164/// \param TemplateArgs the template argument list from which template
6165/// parameters will be deduced.
6166///
6167/// \param Used a bit vector whose elements will be set to \c true
6168/// to indicate when the corresponding template parameter will be
6169/// deduced.
6170void
6171Sema::MarkUsedTemplateParameters(const TemplateArgumentList &TemplateArgs,
                               bool OnlyDeduced, unsigned Depth,
                               llvm::SmallBitVector &Used) {
// C++0x [temp.deduct.type]p9:
//   If the template argument list of P contains a pack expansion that is not
//   the last template argument, the entire template argument list is a
//   non-deduced context.
if (OnlyDeduced &&
    hasPackExpansionBeforeEnd(TemplateArgs.asArray()))
  return;

for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
  ::MarkUsedTemplateParameters(Context, TemplateArgs[I], OnlyDeduced,
                               Depth, Used);
6185}

6187/// Marks all of the template parameters that will be deduced by a
6188/// call to the given function template.
6189void Sema::MarkDeducedTemplateParameters(
  ASTContext &Ctx, const FunctionTemplateDecl *FunctionTemplate,
  llvm::SmallBitVector &Deduced) {
TemplateParameterList *TemplateParams
  = FunctionTemplate->getTemplateParameters();
Deduced.clear();
Deduced.resize(TemplateParams->size());

FunctionDecl *Function = FunctionTemplate->getTemplatedDecl();
for (unsigned I = 0, N = Function->getNumParams(); I != N; ++I)
  ::MarkUsedTemplateParameters(Ctx, Function->getParamDecl(I)->getType(),
                               true, TemplateParams->getDepth(), Deduced);
6201}

6203bool hasDeducibleTemplateParameters(Sema &S,
                                  FunctionTemplateDecl *FunctionTemplate,
                                  QualType T) {
if (!T->isDependentType())
  return false;

TemplateParameterList *TemplateParams
  = FunctionTemplate->getTemplateParameters();
llvm::SmallBitVector Deduced(TemplateParams->size());
::MarkUsedTemplateParameters(S.Context, T, true, TemplateParams->getDepth(),
                             Deduced);

return Deduced.any();
6216}