Bug Summary

File:src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Analysis/LoopAccessAnalysis.cpp
Warning:line 211, column 15
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple amd64-unknown-openbsd7.0 -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name LoopAccessAnalysis.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -mrelocation-model pic -pic-level 1 -fhalf-no-semantic-interposition -mframe-pointer=all -relaxed-aliasing -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fcoverage-compilation-dir=/usr/src/gnu/usr.bin/clang/libLLVM/obj -resource-dir /usr/local/lib/clang/13.0.0 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/AMDGPU -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Analysis -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ASMParser -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/BinaryFormat -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitcode -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitcode -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Bitstream -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /include/llvm/CodeGen -I /include/llvm/CodeGen/PBQP -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/IR -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/IR -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Coroutines -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ProfileData/Coverage -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/CodeView -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/DWARF -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/MSF -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/PDB -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Demangle -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine/JITLink -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ExecutionEngine/Orc -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend/OpenACC -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Frontend/OpenMP -I /include/llvm/CodeGen/GlobalISel -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/IRReader -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/InstCombine -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/Transforms/InstCombine -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/LTO -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Linker -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/MC -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/MC/MCParser -I /include/llvm/CodeGen/MIRParser -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Object -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Option -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Passes -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ProfileData -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Scalar -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/ADT -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Support -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/DebugInfo/Symbolize -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Target -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Utils -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/Vectorize -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include/llvm/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Target/X86 -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include/llvm/Transforms/IPO -I /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/include -I /usr/src/gnu/usr.bin/clang/libLLVM/../include -I /usr/src/gnu/usr.bin/clang/libLLVM/obj -I /usr/src/gnu/usr.bin/clang/libLLVM/obj/../include -D NDEBUG -D __STDC_LIMIT_MACROS -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D LLVM_PREFIX="/usr" -D PIC -internal-isystem /usr/include/c++/v1 -internal-isystem /usr/local/lib/clang/13.0.0/include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/usr/src/gnu/usr.bin/clang/libLLVM/obj -ferror-limit 19 -fvisibility-inlines-hidden -fwrapv -D_RET_PROTECTOR -ret-protector -fno-rtti -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -fno-builtin-malloc -fno-builtin-calloc -fno-builtin-realloc -fno-builtin-valloc -fno-builtin-free -fno-builtin-strdup -fno-builtin-strndup -analyzer-output=html -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /home/ben/Projects/vmm/scan-build/2022-01-12-194120-40624-1 -x c++ /usr/src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Analysis/LoopAccessAnalysis.cpp
1//===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==//
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// The implementation for the loop memory dependence that was originally
10// developed for the loop vectorizer.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Analysis/LoopAccessAnalysis.h"
15#include "llvm/ADT/APInt.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/DepthFirstIterator.h"
18#include "llvm/ADT/EquivalenceClasses.h"
19#include "llvm/ADT/PointerIntPair.h"
20#include "llvm/ADT/STLExtras.h"
21#include "llvm/ADT/SetVector.h"
22#include "llvm/ADT/SmallPtrSet.h"
23#include "llvm/ADT/SmallSet.h"
24#include "llvm/ADT/SmallVector.h"
25#include "llvm/ADT/iterator_range.h"
26#include "llvm/Analysis/AliasAnalysis.h"
27#include "llvm/Analysis/AliasSetTracker.h"
28#include "llvm/Analysis/LoopAnalysisManager.h"
29#include "llvm/Analysis/LoopInfo.h"
30#include "llvm/Analysis/MemoryLocation.h"
31#include "llvm/Analysis/OptimizationRemarkEmitter.h"
32#include "llvm/Analysis/ScalarEvolution.h"
33#include "llvm/Analysis/ScalarEvolutionExpressions.h"
34#include "llvm/Analysis/TargetLibraryInfo.h"
35#include "llvm/Analysis/ValueTracking.h"
36#include "llvm/Analysis/VectorUtils.h"
37#include "llvm/IR/BasicBlock.h"
38#include "llvm/IR/Constants.h"
39#include "llvm/IR/DataLayout.h"
40#include "llvm/IR/DebugLoc.h"
41#include "llvm/IR/DerivedTypes.h"
42#include "llvm/IR/DiagnosticInfo.h"
43#include "llvm/IR/Dominators.h"
44#include "llvm/IR/Function.h"
45#include "llvm/IR/InstrTypes.h"
46#include "llvm/IR/Instruction.h"
47#include "llvm/IR/Instructions.h"
48#include "llvm/IR/Operator.h"
49#include "llvm/IR/PassManager.h"
50#include "llvm/IR/Type.h"
51#include "llvm/IR/Value.h"
52#include "llvm/IR/ValueHandle.h"
53#include "llvm/InitializePasses.h"
54#include "llvm/Pass.h"
55#include "llvm/Support/Casting.h"
56#include "llvm/Support/CommandLine.h"
57#include "llvm/Support/Debug.h"
58#include "llvm/Support/ErrorHandling.h"
59#include "llvm/Support/raw_ostream.h"
60#include <algorithm>
61#include <cassert>
62#include <cstdint>
63#include <cstdlib>
64#include <iterator>
65#include <utility>
66#include <vector>
67
68using namespace llvm;
69
70#define DEBUG_TYPE"loop-accesses" "loop-accesses"
71
72static cl::opt<unsigned, true>
73VectorizationFactor("force-vector-width", cl::Hidden,
74 cl::desc("Sets the SIMD width. Zero is autoselect."),
75 cl::location(VectorizerParams::VectorizationFactor));
76unsigned VectorizerParams::VectorizationFactor;
77
78static cl::opt<unsigned, true>
79VectorizationInterleave("force-vector-interleave", cl::Hidden,
80 cl::desc("Sets the vectorization interleave count. "
81 "Zero is autoselect."),
82 cl::location(
83 VectorizerParams::VectorizationInterleave));
84unsigned VectorizerParams::VectorizationInterleave;
85
86static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold(
87 "runtime-memory-check-threshold", cl::Hidden,
88 cl::desc("When performing memory disambiguation checks at runtime do not "
89 "generate more than this number of comparisons (default = 8)."),
90 cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8));
91unsigned VectorizerParams::RuntimeMemoryCheckThreshold;
92
93/// The maximum iterations used to merge memory checks
94static cl::opt<unsigned> MemoryCheckMergeThreshold(
95 "memory-check-merge-threshold", cl::Hidden,
96 cl::desc("Maximum number of comparisons done when trying to merge "
97 "runtime memory checks. (default = 100)"),
98 cl::init(100));
99
100/// Maximum SIMD width.
101const unsigned VectorizerParams::MaxVectorWidth = 64;
102
103/// We collect dependences up to this threshold.
104static cl::opt<unsigned>
105 MaxDependences("max-dependences", cl::Hidden,
106 cl::desc("Maximum number of dependences collected by "
107 "loop-access analysis (default = 100)"),
108 cl::init(100));
109
110/// This enables versioning on the strides of symbolically striding memory
111/// accesses in code like the following.
112/// for (i = 0; i < N; ++i)
113/// A[i * Stride1] += B[i * Stride2] ...
114///
115/// Will be roughly translated to
116/// if (Stride1 == 1 && Stride2 == 1) {
117/// for (i = 0; i < N; i+=4)
118/// A[i:i+3] += ...
119/// } else
120/// ...
121static cl::opt<bool> EnableMemAccessVersioning(
122 "enable-mem-access-versioning", cl::init(true), cl::Hidden,
123 cl::desc("Enable symbolic stride memory access versioning"));
124
125/// Enable store-to-load forwarding conflict detection. This option can
126/// be disabled for correctness testing.
127static cl::opt<bool> EnableForwardingConflictDetection(
128 "store-to-load-forwarding-conflict-detection", cl::Hidden,
129 cl::desc("Enable conflict detection in loop-access analysis"),
130 cl::init(true));
131
132bool VectorizerParams::isInterleaveForced() {
133 return ::VectorizationInterleave.getNumOccurrences() > 0;
134}
135
136Value *llvm::stripIntegerCast(Value *V) {
137 if (auto *CI = dyn_cast<CastInst>(V))
138 if (CI->getOperand(0)->getType()->isIntegerTy())
139 return CI->getOperand(0);
140 return V;
141}
142
143const SCEV *llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE,
144 const ValueToValueMap &PtrToStride,
145 Value *Ptr, Value *OrigPtr) {
146 const SCEV *OrigSCEV = PSE.getSCEV(Ptr);
147
148 // If there is an entry in the map return the SCEV of the pointer with the
149 // symbolic stride replaced by one.
150 ValueToValueMap::const_iterator SI =
151 PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
152 if (SI == PtrToStride.end())
153 // For a non-symbolic stride, just return the original expression.
154 return OrigSCEV;
155
156 Value *StrideVal = stripIntegerCast(SI->second);
157
158 ScalarEvolution *SE = PSE.getSE();
159 const auto *U = cast<SCEVUnknown>(SE->getSCEV(StrideVal));
160 const auto *CT =
161 static_cast<const SCEVConstant *>(SE->getOne(StrideVal->getType()));
162
163 PSE.addPredicate(*SE->getEqualPredicate(U, CT));
164 auto *Expr = PSE.getSCEV(Ptr);
165
166 LLVM_DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEVdo { } while (false)
167 << " by: " << *Expr << "\n")do { } while (false);
168 return Expr;
169}
170
171RuntimeCheckingPtrGroup::RuntimeCheckingPtrGroup(
172 unsigned Index, RuntimePointerChecking &RtCheck)
173 : High(RtCheck.Pointers[Index].End), Low(RtCheck.Pointers[Index].Start),
174 AddressSpace(RtCheck.Pointers[Index]
175 .PointerValue->getType()
176 ->getPointerAddressSpace()) {
177 Members.push_back(Index);
178}
179
180/// Calculate Start and End points of memory access.
181/// Let's assume A is the first access and B is a memory access on N-th loop
182/// iteration. Then B is calculated as:
183/// B = A + Step*N .
184/// Step value may be positive or negative.
185/// N is a calculated back-edge taken count:
186/// N = (TripCount > 0) ? RoundDown(TripCount -1 , VF) : 0
187/// Start and End points are calculated in the following way:
188/// Start = UMIN(A, B) ; End = UMAX(A, B) + SizeOfElt,
189/// where SizeOfElt is the size of single memory access in bytes.
190///
191/// There is no conflict when the intervals are disjoint:
192/// NoConflict = (P2.Start >= P1.End) || (P1.Start >= P2.End)
193void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr,
194 unsigned DepSetId, unsigned ASId,
195 const ValueToValueMap &Strides,
196 PredicatedScalarEvolution &PSE) {
197 // Get the stride replaced scev.
198 const SCEV *Sc = replaceSymbolicStrideSCEV(PSE, Strides, Ptr);
199 ScalarEvolution *SE = PSE.getSE();
200
201 const SCEV *ScStart;
202 const SCEV *ScEnd;
203
204 if (SE->isLoopInvariant(Sc, Lp)) {
23
Assuming the condition is false
24
Taking false branch
205 ScStart = ScEnd = Sc;
206 } else {
207 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
25
Assuming 'Sc' is not a 'SCEVAddRecExpr'
26
'AR' initialized to a null pointer value
208 assert(AR && "Invalid addrec expression")((void)0);
209 const SCEV *Ex = PSE.getBackedgeTakenCount();
210
211 ScStart = AR->getStart();
27
Called C++ object pointer is null
212 ScEnd = AR->evaluateAtIteration(Ex, *SE);
213 const SCEV *Step = AR->getStepRecurrence(*SE);
214
215 // For expressions with negative step, the upper bound is ScStart and the
216 // lower bound is ScEnd.
217 if (const auto *CStep = dyn_cast<SCEVConstant>(Step)) {
218 if (CStep->getValue()->isNegative())
219 std::swap(ScStart, ScEnd);
220 } else {
221 // Fallback case: the step is not constant, but we can still
222 // get the upper and lower bounds of the interval by using min/max
223 // expressions.
224 ScStart = SE->getUMinExpr(ScStart, ScEnd);
225 ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd);
226 }
227 }
228 // Add the size of the pointed element to ScEnd.
229 auto &DL = Lp->getHeader()->getModule()->getDataLayout();
230 Type *IdxTy = DL.getIndexType(Ptr->getType());
231 const SCEV *EltSizeSCEV =
232 SE->getStoreSizeOfExpr(IdxTy, Ptr->getType()->getPointerElementType());
233 ScEnd = SE->getAddExpr(ScEnd, EltSizeSCEV);
234
235 Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc);
236}
237
238SmallVector<RuntimePointerCheck, 4>
239RuntimePointerChecking::generateChecks() const {
240 SmallVector<RuntimePointerCheck, 4> Checks;
241
242 for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
243 for (unsigned J = I + 1; J < CheckingGroups.size(); ++J) {
244 const RuntimeCheckingPtrGroup &CGI = CheckingGroups[I];
245 const RuntimeCheckingPtrGroup &CGJ = CheckingGroups[J];
246
247 if (needsChecking(CGI, CGJ))
248 Checks.push_back(std::make_pair(&CGI, &CGJ));
249 }
250 }
251 return Checks;
252}
253
254void RuntimePointerChecking::generateChecks(
255 MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) {
256 assert(Checks.empty() && "Checks is not empty")((void)0);
257 groupChecks(DepCands, UseDependencies);
258 Checks = generateChecks();
259}
260
261bool RuntimePointerChecking::needsChecking(
262 const RuntimeCheckingPtrGroup &M, const RuntimeCheckingPtrGroup &N) const {
263 for (unsigned I = 0, EI = M.Members.size(); EI != I; ++I)
264 for (unsigned J = 0, EJ = N.Members.size(); EJ != J; ++J)
265 if (needsChecking(M.Members[I], N.Members[J]))
266 return true;
267 return false;
268}
269
270/// Compare \p I and \p J and return the minimum.
271/// Return nullptr in case we couldn't find an answer.
272static const SCEV *getMinFromExprs(const SCEV *I, const SCEV *J,
273 ScalarEvolution *SE) {
274 const SCEV *Diff = SE->getMinusSCEV(J, I);
275 const SCEVConstant *C = dyn_cast<const SCEVConstant>(Diff);
276
277 if (!C)
278 return nullptr;
279 if (C->getValue()->isNegative())
280 return J;
281 return I;
282}
283
284bool RuntimeCheckingPtrGroup::addPointer(unsigned Index,
285 RuntimePointerChecking &RtCheck) {
286 return addPointer(
287 Index, RtCheck.Pointers[Index].Start, RtCheck.Pointers[Index].End,
288 RtCheck.Pointers[Index].PointerValue->getType()->getPointerAddressSpace(),
289 *RtCheck.SE);
290}
291
292bool RuntimeCheckingPtrGroup::addPointer(unsigned Index, const SCEV *Start,
293 const SCEV *End, unsigned AS,
294 ScalarEvolution &SE) {
295 assert(AddressSpace == AS &&((void)0)
296 "all pointers in a checking group must be in the same address space")((void)0);
297
298 // Compare the starts and ends with the known minimum and maximum
299 // of this set. We need to know how we compare against the min/max
300 // of the set in order to be able to emit memchecks.
301 const SCEV *Min0 = getMinFromExprs(Start, Low, &SE);
302 if (!Min0)
303 return false;
304
305 const SCEV *Min1 = getMinFromExprs(End, High, &SE);
306 if (!Min1)
307 return false;
308
309 // Update the low bound expression if we've found a new min value.
310 if (Min0 == Start)
311 Low = Start;
312
313 // Update the high bound expression if we've found a new max value.
314 if (Min1 != End)
315 High = End;
316
317 Members.push_back(Index);
318 return true;
319}
320
321void RuntimePointerChecking::groupChecks(
322 MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) {
323 // We build the groups from dependency candidates equivalence classes
324 // because:
325 // - We know that pointers in the same equivalence class share
326 // the same underlying object and therefore there is a chance
327 // that we can compare pointers
328 // - We wouldn't be able to merge two pointers for which we need
329 // to emit a memcheck. The classes in DepCands are already
330 // conveniently built such that no two pointers in the same
331 // class need checking against each other.
332
333 // We use the following (greedy) algorithm to construct the groups
334 // For every pointer in the equivalence class:
335 // For each existing group:
336 // - if the difference between this pointer and the min/max bounds
337 // of the group is a constant, then make the pointer part of the
338 // group and update the min/max bounds of that group as required.
339
340 CheckingGroups.clear();
341
342 // If we need to check two pointers to the same underlying object
343 // with a non-constant difference, we shouldn't perform any pointer
344 // grouping with those pointers. This is because we can easily get
345 // into cases where the resulting check would return false, even when
346 // the accesses are safe.
347 //
348 // The following example shows this:
349 // for (i = 0; i < 1000; ++i)
350 // a[5000 + i * m] = a[i] + a[i + 9000]
351 //
352 // Here grouping gives a check of (5000, 5000 + 1000 * m) against
353 // (0, 10000) which is always false. However, if m is 1, there is no
354 // dependence. Not grouping the checks for a[i] and a[i + 9000] allows
355 // us to perform an accurate check in this case.
356 //
357 // The above case requires that we have an UnknownDependence between
358 // accesses to the same underlying object. This cannot happen unless
359 // FoundNonConstantDistanceDependence is set, and therefore UseDependencies
360 // is also false. In this case we will use the fallback path and create
361 // separate checking groups for all pointers.
362
363 // If we don't have the dependency partitions, construct a new
364 // checking pointer group for each pointer. This is also required
365 // for correctness, because in this case we can have checking between
366 // pointers to the same underlying object.
367 if (!UseDependencies) {
368 for (unsigned I = 0; I < Pointers.size(); ++I)
369 CheckingGroups.push_back(RuntimeCheckingPtrGroup(I, *this));
370 return;
371 }
372
373 unsigned TotalComparisons = 0;
374
375 DenseMap<Value *, unsigned> PositionMap;
376 for (unsigned Index = 0; Index < Pointers.size(); ++Index)
377 PositionMap[Pointers[Index].PointerValue] = Index;
378
379 // We need to keep track of what pointers we've already seen so we
380 // don't process them twice.
381 SmallSet<unsigned, 2> Seen;
382
383 // Go through all equivalence classes, get the "pointer check groups"
384 // and add them to the overall solution. We use the order in which accesses
385 // appear in 'Pointers' to enforce determinism.
386 for (unsigned I = 0; I < Pointers.size(); ++I) {
387 // We've seen this pointer before, and therefore already processed
388 // its equivalence class.
389 if (Seen.count(I))
390 continue;
391
392 MemoryDepChecker::MemAccessInfo Access(Pointers[I].PointerValue,
393 Pointers[I].IsWritePtr);
394
395 SmallVector<RuntimeCheckingPtrGroup, 2> Groups;
396 auto LeaderI = DepCands.findValue(DepCands.getLeaderValue(Access));
397
398 // Because DepCands is constructed by visiting accesses in the order in
399 // which they appear in alias sets (which is deterministic) and the
400 // iteration order within an equivalence class member is only dependent on
401 // the order in which unions and insertions are performed on the
402 // equivalence class, the iteration order is deterministic.
403 for (auto MI = DepCands.member_begin(LeaderI), ME = DepCands.member_end();
404 MI != ME; ++MI) {
405 auto PointerI = PositionMap.find(MI->getPointer());
406 assert(PointerI != PositionMap.end() &&((void)0)
407 "pointer in equivalence class not found in PositionMap")((void)0);
408 unsigned Pointer = PointerI->second;
409 bool Merged = false;
410 // Mark this pointer as seen.
411 Seen.insert(Pointer);
412
413 // Go through all the existing sets and see if we can find one
414 // which can include this pointer.
415 for (RuntimeCheckingPtrGroup &Group : Groups) {
416 // Don't perform more than a certain amount of comparisons.
417 // This should limit the cost of grouping the pointers to something
418 // reasonable. If we do end up hitting this threshold, the algorithm
419 // will create separate groups for all remaining pointers.
420 if (TotalComparisons > MemoryCheckMergeThreshold)
421 break;
422
423 TotalComparisons++;
424
425 if (Group.addPointer(Pointer, *this)) {
426 Merged = true;
427 break;
428 }
429 }
430
431 if (!Merged)
432 // We couldn't add this pointer to any existing set or the threshold
433 // for the number of comparisons has been reached. Create a new group
434 // to hold the current pointer.
435 Groups.push_back(RuntimeCheckingPtrGroup(Pointer, *this));
436 }
437
438 // We've computed the grouped checks for this partition.
439 // Save the results and continue with the next one.
440 llvm::copy(Groups, std::back_inserter(CheckingGroups));
441 }
442}
443
444bool RuntimePointerChecking::arePointersInSamePartition(
445 const SmallVectorImpl<int> &PtrToPartition, unsigned PtrIdx1,
446 unsigned PtrIdx2) {
447 return (PtrToPartition[PtrIdx1] != -1 &&
448 PtrToPartition[PtrIdx1] == PtrToPartition[PtrIdx2]);
449}
450
451bool RuntimePointerChecking::needsChecking(unsigned I, unsigned J) const {
452 const PointerInfo &PointerI = Pointers[I];
453 const PointerInfo &PointerJ = Pointers[J];
454
455 // No need to check if two readonly pointers intersect.
456 if (!PointerI.IsWritePtr && !PointerJ.IsWritePtr)
457 return false;
458
459 // Only need to check pointers between two different dependency sets.
460 if (PointerI.DependencySetId == PointerJ.DependencySetId)
461 return false;
462
463 // Only need to check pointers in the same alias set.
464 if (PointerI.AliasSetId != PointerJ.AliasSetId)
465 return false;
466
467 return true;
468}
469
470void RuntimePointerChecking::printChecks(
471 raw_ostream &OS, const SmallVectorImpl<RuntimePointerCheck> &Checks,
472 unsigned Depth) const {
473 unsigned N = 0;
474 for (const auto &Check : Checks) {
475 const auto &First = Check.first->Members, &Second = Check.second->Members;
476
477 OS.indent(Depth) << "Check " << N++ << ":\n";
478
479 OS.indent(Depth + 2) << "Comparing group (" << Check.first << "):\n";
480 for (unsigned K = 0; K < First.size(); ++K)
481 OS.indent(Depth + 2) << *Pointers[First[K]].PointerValue << "\n";
482
483 OS.indent(Depth + 2) << "Against group (" << Check.second << "):\n";
484 for (unsigned K = 0; K < Second.size(); ++K)
485 OS.indent(Depth + 2) << *Pointers[Second[K]].PointerValue << "\n";
486 }
487}
488
489void RuntimePointerChecking::print(raw_ostream &OS, unsigned Depth) const {
490
491 OS.indent(Depth) << "Run-time memory checks:\n";
492 printChecks(OS, Checks, Depth);
493
494 OS.indent(Depth) << "Grouped accesses:\n";
495 for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
496 const auto &CG = CheckingGroups[I];
497
498 OS.indent(Depth + 2) << "Group " << &CG << ":\n";
499 OS.indent(Depth + 4) << "(Low: " << *CG.Low << " High: " << *CG.High
500 << ")\n";
501 for (unsigned J = 0; J < CG.Members.size(); ++J) {
502 OS.indent(Depth + 6) << "Member: " << *Pointers[CG.Members[J]].Expr
503 << "\n";
504 }
505 }
506}
507
508namespace {
509
510/// Analyses memory accesses in a loop.
511///
512/// Checks whether run time pointer checks are needed and builds sets for data
513/// dependence checking.
514class AccessAnalysis {
515public:
516 /// Read or write access location.
517 typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
518 typedef SmallVector<MemAccessInfo, 8> MemAccessInfoList;
519
520 AccessAnalysis(Loop *TheLoop, AAResults *AA, LoopInfo *LI,
521 MemoryDepChecker::DepCandidates &DA,
522 PredicatedScalarEvolution &PSE)
523 : TheLoop(TheLoop), AST(*AA), LI(LI), DepCands(DA),
524 IsRTCheckAnalysisNeeded(false), PSE(PSE) {}
525
526 /// Register a load and whether it is only read from.
527 void addLoad(MemoryLocation &Loc, bool IsReadOnly) {
528 Value *Ptr = const_cast<Value*>(Loc.Ptr);
529 AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags);
530 Accesses.insert(MemAccessInfo(Ptr, false));
531 if (IsReadOnly)
532 ReadOnlyPtr.insert(Ptr);
533 }
534
535 /// Register a store.
536 void addStore(MemoryLocation &Loc) {
537 Value *Ptr = const_cast<Value*>(Loc.Ptr);
538 AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags);
539 Accesses.insert(MemAccessInfo(Ptr, true));
540 }
541
542 /// Check if we can emit a run-time no-alias check for \p Access.
543 ///
544 /// Returns true if we can emit a run-time no alias check for \p Access.
545 /// If we can check this access, this also adds it to a dependence set and
546 /// adds a run-time to check for it to \p RtCheck. If \p Assume is true,
547 /// we will attempt to use additional run-time checks in order to get
548 /// the bounds of the pointer.
549 bool createCheckForAccess(RuntimePointerChecking &RtCheck,
550 MemAccessInfo Access,
551 const ValueToValueMap &Strides,
552 DenseMap<Value *, unsigned> &DepSetId,
553 Loop *TheLoop, unsigned &RunningDepId,
554 unsigned ASId, bool ShouldCheckStride,
555 bool Assume);
556
557 /// Check whether we can check the pointers at runtime for
558 /// non-intersection.
559 ///
560 /// Returns true if we need no check or if we do and we can generate them
561 /// (i.e. the pointers have computable bounds).
562 bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE,
563 Loop *TheLoop, const ValueToValueMap &Strides,
564 bool ShouldCheckWrap = false);
565
566 /// Goes over all memory accesses, checks whether a RT check is needed
567 /// and builds sets of dependent accesses.
568 void buildDependenceSets() {
569 processMemAccesses();
570 }
571
572 /// Initial processing of memory accesses determined that we need to
573 /// perform dependency checking.
574 ///
575 /// Note that this can later be cleared if we retry memcheck analysis without
576 /// dependency checking (i.e. FoundNonConstantDistanceDependence).
577 bool isDependencyCheckNeeded() { return !CheckDeps.empty(); }
578
579 /// We decided that no dependence analysis would be used. Reset the state.
580 void resetDepChecks(MemoryDepChecker &DepChecker) {
581 CheckDeps.clear();
582 DepChecker.clearDependences();
583 }
584
585 MemAccessInfoList &getDependenciesToCheck() { return CheckDeps; }
586
587private:
588 typedef SetVector<MemAccessInfo> PtrAccessSet;
589
590 /// Go over all memory access and check whether runtime pointer checks
591 /// are needed and build sets of dependency check candidates.
592 void processMemAccesses();
593
594 /// Set of all accesses.
595 PtrAccessSet Accesses;
596
597 /// The loop being checked.
598 const Loop *TheLoop;
599
600 /// List of accesses that need a further dependence check.
601 MemAccessInfoList CheckDeps;
602
603 /// Set of pointers that are read only.
604 SmallPtrSet<Value*, 16> ReadOnlyPtr;
605
606 /// An alias set tracker to partition the access set by underlying object and
607 //intrinsic property (such as TBAA metadata).
608 AliasSetTracker AST;
609
610 LoopInfo *LI;
611
612 /// Sets of potentially dependent accesses - members of one set share an
613 /// underlying pointer. The set "CheckDeps" identfies which sets really need a
614 /// dependence check.
615 MemoryDepChecker::DepCandidates &DepCands;
616
617 /// Initial processing of memory accesses determined that we may need
618 /// to add memchecks. Perform the analysis to determine the necessary checks.
619 ///
620 /// Note that, this is different from isDependencyCheckNeeded. When we retry
621 /// memcheck analysis without dependency checking
622 /// (i.e. FoundNonConstantDistanceDependence), isDependencyCheckNeeded is
623 /// cleared while this remains set if we have potentially dependent accesses.
624 bool IsRTCheckAnalysisNeeded;
625
626 /// The SCEV predicate containing all the SCEV-related assumptions.
627 PredicatedScalarEvolution &PSE;
628};
629
630} // end anonymous namespace
631
632/// Check whether a pointer can participate in a runtime bounds check.
633/// If \p Assume, try harder to prove that we can compute the bounds of \p Ptr
634/// by adding run-time checks (overflow checks) if necessary.
635static bool hasComputableBounds(PredicatedScalarEvolution &PSE,
636 const ValueToValueMap &Strides, Value *Ptr,
637 Loop *L, bool Assume) {
638 const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, Strides, Ptr);
639
640 // The bounds for loop-invariant pointer is trivial.
641 if (PSE.getSE()->isLoopInvariant(PtrScev, L))
642 return true;
643
644 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
645
646 if (!AR && Assume)
647 AR = PSE.getAsAddRec(Ptr);
648
649 if (!AR)
650 return false;
651
652 return AR->isAffine();
653}
654
655/// Check whether a pointer address cannot wrap.
656static bool isNoWrap(PredicatedScalarEvolution &PSE,
657 const ValueToValueMap &Strides, Value *Ptr, Loop *L) {
658 const SCEV *PtrScev = PSE.getSCEV(Ptr);
659 if (PSE.getSE()->isLoopInvariant(PtrScev, L))
660 return true;
661
662 int64_t Stride = getPtrStride(PSE, Ptr, L, Strides);
663 if (Stride == 1 || PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW))
664 return true;
665
666 return false;
667}
668
669bool AccessAnalysis::createCheckForAccess(RuntimePointerChecking &RtCheck,
670 MemAccessInfo Access,
671 const ValueToValueMap &StridesMap,
672 DenseMap<Value *, unsigned> &DepSetId,
673 Loop *TheLoop, unsigned &RunningDepId,
674 unsigned ASId, bool ShouldCheckWrap,
675 bool Assume) {
676 Value *Ptr = Access.getPointer();
677
678 if (!hasComputableBounds(PSE, StridesMap, Ptr, TheLoop, Assume))
20
Taking false branch
679 return false;
680
681 // When we run after a failing dependency check we have to make sure
682 // we don't have wrapping pointers.
683 if (ShouldCheckWrap
20.1
'ShouldCheckWrap' is false
&& !isNoWrap(PSE, StridesMap, Ptr, TheLoop)) {
684 auto *Expr = PSE.getSCEV(Ptr);
685 if (!Assume || !isa<SCEVAddRecExpr>(Expr))
686 return false;
687 PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW);
688 }
689
690 // The id of the dependence set.
691 unsigned DepId;
692
693 if (isDependencyCheckNeeded()) {
21
Taking false branch
694 Value *Leader = DepCands.getLeaderValue(Access).getPointer();
695 unsigned &LeaderId = DepSetId[Leader];
696 if (!LeaderId)
697 LeaderId = RunningDepId++;
698 DepId = LeaderId;
699 } else
700 // Each access has its own dependence set.
701 DepId = RunningDepId++;
702
703 bool IsWrite = Access.getInt();
704 RtCheck.insert(TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap, PSE);
22
Calling 'RuntimePointerChecking::insert'
705 LLVM_DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n')do { } while (false);
706
707 return true;
708 }
709
710bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
711 ScalarEvolution *SE, Loop *TheLoop,
712 const ValueToValueMap &StridesMap,
713 bool ShouldCheckWrap) {
714 // Find pointers with computable bounds. We are going to use this information
715 // to place a runtime bound check.
716 bool CanDoRT = true;
717
718 bool MayNeedRTCheck = false;
719 if (!IsRTCheckAnalysisNeeded) return true;
11
Assuming field 'IsRTCheckAnalysisNeeded' is true
12
Taking false branch
720
721 bool IsDepCheckNeeded = isDependencyCheckNeeded();
722
723 // We assign a consecutive id to access from different alias sets.
724 // Accesses between different groups doesn't need to be checked.
725 unsigned ASId = 0;
726 for (auto &AS : AST) {
727 int NumReadPtrChecks = 0;
728 int NumWritePtrChecks = 0;
729 bool CanDoAliasSetRT = true;
730 ++ASId;
731
732 // We assign consecutive id to access from different dependence sets.
733 // Accesses within the same set don't need a runtime check.
734 unsigned RunningDepId = 1;
735 DenseMap<Value *, unsigned> DepSetId;
736
737 SmallVector<MemAccessInfo, 4> Retries;
738
739 // First, count how many write and read accesses are in the alias set. Also
740 // collect MemAccessInfos for later.
741 SmallVector<MemAccessInfo, 4> AccessInfos;
742 for (const auto &A : AS) {
743 Value *Ptr = A.getValue();
744 bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true));
745
746 if (IsWrite)
13
Assuming 'IsWrite' is false
14
Taking false branch
15
Assuming 'IsWrite' is true
16
Taking true branch
747 ++NumWritePtrChecks;
748 else
749 ++NumReadPtrChecks;
750 AccessInfos.emplace_back(Ptr, IsWrite);
751 }
752
753 // We do not need runtime checks for this alias set, if there are no writes
754 // or a single write and no reads.
755 if (NumWritePtrChecks
16.1
'NumWritePtrChecks' is not equal to 0
== 0 ||
17
Taking false branch
756 (NumWritePtrChecks
16.2
'NumWritePtrChecks' is equal to 1
== 1 && NumReadPtrChecks
16.3
'NumReadPtrChecks' is not equal to 0
== 0)) {
757 assert((AS.size() <= 1 ||((void)0)
758 all_of(AS,((void)0)
759 [this](auto AC) {((void)0)
760 MemAccessInfo AccessWrite(AC.getValue(), true);((void)0)
761 return DepCands.findValue(AccessWrite) == DepCands.end();((void)0)
762 })) &&((void)0)
763 "Can only skip updating CanDoRT below, if all entries in AS "((void)0)
764 "are reads or there is at most 1 entry")((void)0);
765 continue;
766 }
767
768 for (auto &Access : AccessInfos) {
18
Assuming '__begin2' is not equal to '__end2'
769 if (!createCheckForAccess(RtCheck, Access, StridesMap, DepSetId, TheLoop,
19
Calling 'AccessAnalysis::createCheckForAccess'
770 RunningDepId, ASId, ShouldCheckWrap, false)) {
771 LLVM_DEBUG(dbgs() << "LAA: Can't find bounds for ptr:"do { } while (false)
772 << *Access.getPointer() << '\n')do { } while (false);
773 Retries.push_back(Access);
774 CanDoAliasSetRT = false;
775 }
776 }
777
778 // Note that this function computes CanDoRT and MayNeedRTCheck
779 // independently. For example CanDoRT=false, MayNeedRTCheck=false means that
780 // we have a pointer for which we couldn't find the bounds but we don't
781 // actually need to emit any checks so it does not matter.
782 //
783 // We need runtime checks for this alias set, if there are at least 2
784 // dependence sets (in which case RunningDepId > 2) or if we need to re-try
785 // any bound checks (because in that case the number of dependence sets is
786 // incomplete).
787 bool NeedsAliasSetRTCheck = RunningDepId > 2 || !Retries.empty();
788
789 // We need to perform run-time alias checks, but some pointers had bounds
790 // that couldn't be checked.
791 if (NeedsAliasSetRTCheck && !CanDoAliasSetRT) {
792 // Reset the CanDoSetRt flag and retry all accesses that have failed.
793 // We know that we need these checks, so we can now be more aggressive
794 // and add further checks if required (overflow checks).
795 CanDoAliasSetRT = true;
796 for (auto Access : Retries)
797 if (!createCheckForAccess(RtCheck, Access, StridesMap, DepSetId,
798 TheLoop, RunningDepId, ASId,
799 ShouldCheckWrap, /*Assume=*/true)) {
800 CanDoAliasSetRT = false;
801 break;
802 }
803 }
804
805 CanDoRT &= CanDoAliasSetRT;
806 MayNeedRTCheck |= NeedsAliasSetRTCheck;
807 ++ASId;
808 }
809
810 // If the pointers that we would use for the bounds comparison have different
811 // address spaces, assume the values aren't directly comparable, so we can't
812 // use them for the runtime check. We also have to assume they could
813 // overlap. In the future there should be metadata for whether address spaces
814 // are disjoint.
815 unsigned NumPointers = RtCheck.Pointers.size();
816 for (unsigned i = 0; i < NumPointers; ++i) {
817 for (unsigned j = i + 1; j < NumPointers; ++j) {
818 // Only need to check pointers between two different dependency sets.
819 if (RtCheck.Pointers[i].DependencySetId ==
820 RtCheck.Pointers[j].DependencySetId)
821 continue;
822 // Only need to check pointers in the same alias set.
823 if (RtCheck.Pointers[i].AliasSetId != RtCheck.Pointers[j].AliasSetId)
824 continue;
825
826 Value *PtrI = RtCheck.Pointers[i].PointerValue;
827 Value *PtrJ = RtCheck.Pointers[j].PointerValue;
828
829 unsigned ASi = PtrI->getType()->getPointerAddressSpace();
830 unsigned ASj = PtrJ->getType()->getPointerAddressSpace();
831 if (ASi != ASj) {
832 LLVM_DEBUG(do { } while (false)
833 dbgs() << "LAA: Runtime check would require comparison between"do { } while (false)
834 " different address spaces\n")do { } while (false);
835 return false;
836 }
837 }
838 }
839
840 if (MayNeedRTCheck && CanDoRT)
841 RtCheck.generateChecks(DepCands, IsDepCheckNeeded);
842
843 LLVM_DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks()do { } while (false)
844 << " pointer comparisons.\n")do { } while (false);
845
846 // If we can do run-time checks, but there are no checks, no runtime checks
847 // are needed. This can happen when all pointers point to the same underlying
848 // object for example.
849 RtCheck.Need = CanDoRT ? RtCheck.getNumberOfChecks() != 0 : MayNeedRTCheck;
850
851 bool CanDoRTIfNeeded = !RtCheck.Need || CanDoRT;
852 if (!CanDoRTIfNeeded)
853 RtCheck.reset();
854 return CanDoRTIfNeeded;
855}
856
857void AccessAnalysis::processMemAccesses() {
858 // We process the set twice: first we process read-write pointers, last we
859 // process read-only pointers. This allows us to skip dependence tests for
860 // read-only pointers.
861
862 LLVM_DEBUG(dbgs() << "LAA: Processing memory accesses...\n")do { } while (false);
863 LLVM_DEBUG(dbgs() << " AST: "; AST.dump())do { } while (false);
864 LLVM_DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n")do { } while (false);
865 LLVM_DEBUG({do { } while (false)
866 for (auto A : Accesses)do { } while (false)
867 dbgs() << "\t" << *A.getPointer() << " (" <<do { } while (false)
868 (A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ?do { } while (false)
869 "read-only" : "read")) << ")\n";do { } while (false)
870 })do { } while (false);
871
872 // The AliasSetTracker has nicely partitioned our pointers by metadata
873 // compatibility and potential for underlying-object overlap. As a result, we
874 // only need to check for potential pointer dependencies within each alias
875 // set.
876 for (const auto &AS : AST) {
877 // Note that both the alias-set tracker and the alias sets themselves used
878 // linked lists internally and so the iteration order here is deterministic
879 // (matching the original instruction order within each set).
880
881 bool SetHasWrite = false;
882
883 // Map of pointers to last access encountered.
884 typedef DenseMap<const Value*, MemAccessInfo> UnderlyingObjToAccessMap;
885 UnderlyingObjToAccessMap ObjToLastAccess;
886
887 // Set of access to check after all writes have been processed.
888 PtrAccessSet DeferredAccesses;
889
890 // Iterate over each alias set twice, once to process read/write pointers,
891 // and then to process read-only pointers.
892 for (int SetIteration = 0; SetIteration < 2; ++SetIteration) {
893 bool UseDeferred = SetIteration > 0;
894 PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses;
895
896 for (const auto &AV : AS) {
897 Value *Ptr = AV.getValue();
898
899 // For a single memory access in AliasSetTracker, Accesses may contain
900 // both read and write, and they both need to be handled for CheckDeps.
901 for (const auto &AC : S) {
902 if (AC.getPointer() != Ptr)
903 continue;
904
905 bool IsWrite = AC.getInt();
906
907 // If we're using the deferred access set, then it contains only
908 // reads.
909 bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite;
910 if (UseDeferred && !IsReadOnlyPtr)
911 continue;
912 // Otherwise, the pointer must be in the PtrAccessSet, either as a
913 // read or a write.
914 assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||((void)0)
915 S.count(MemAccessInfo(Ptr, false))) &&((void)0)
916 "Alias-set pointer not in the access set?")((void)0);
917
918 MemAccessInfo Access(Ptr, IsWrite);
919 DepCands.insert(Access);
920
921 // Memorize read-only pointers for later processing and skip them in
922 // the first round (they need to be checked after we have seen all
923 // write pointers). Note: we also mark pointer that are not
924 // consecutive as "read-only" pointers (so that we check
925 // "a[b[i]] +="). Hence, we need the second check for "!IsWrite".
926 if (!UseDeferred && IsReadOnlyPtr) {
927 DeferredAccesses.insert(Access);
928 continue;
929 }
930
931 // If this is a write - check other reads and writes for conflicts. If
932 // this is a read only check other writes for conflicts (but only if
933 // there is no other write to the ptr - this is an optimization to
934 // catch "a[i] = a[i] + " without having to do a dependence check).
935 if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) {
936 CheckDeps.push_back(Access);
937 IsRTCheckAnalysisNeeded = true;
938 }
939
940 if (IsWrite)
941 SetHasWrite = true;
942
943 // Create sets of pointers connected by a shared alias set and
944 // underlying object.
945 typedef SmallVector<const Value *, 16> ValueVector;
946 ValueVector TempObjects;
947
948 getUnderlyingObjects(Ptr, TempObjects, LI);
949 LLVM_DEBUG(dbgs()do { } while (false)
950 << "Underlying objects for pointer " << *Ptr << "\n")do { } while (false);
951 for (const Value *UnderlyingObj : TempObjects) {
952 // nullptr never alias, don't join sets for pointer that have "null"
953 // in their UnderlyingObjects list.
954 if (isa<ConstantPointerNull>(UnderlyingObj) &&
955 !NullPointerIsDefined(
956 TheLoop->getHeader()->getParent(),
957 UnderlyingObj->getType()->getPointerAddressSpace()))
958 continue;
959
960 UnderlyingObjToAccessMap::iterator Prev =
961 ObjToLastAccess.find(UnderlyingObj);
962 if (Prev != ObjToLastAccess.end())
963 DepCands.unionSets(Access, Prev->second);
964
965 ObjToLastAccess[UnderlyingObj] = Access;
966 LLVM_DEBUG(dbgs() << " " << *UnderlyingObj << "\n")do { } while (false);
967 }
968 }
969 }
970 }
971 }
972}
973
974static bool isInBoundsGep(Value *Ptr) {
975 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
976 return GEP->isInBounds();
977 return false;
978}
979
980/// Return true if an AddRec pointer \p Ptr is unsigned non-wrapping,
981/// i.e. monotonically increasing/decreasing.
982static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR,
983 PredicatedScalarEvolution &PSE, const Loop *L) {
984 // FIXME: This should probably only return true for NUW.
985 if (AR->getNoWrapFlags(SCEV::NoWrapMask))
986 return true;
987
988 // Scalar evolution does not propagate the non-wrapping flags to values that
989 // are derived from a non-wrapping induction variable because non-wrapping
990 // could be flow-sensitive.
991 //
992 // Look through the potentially overflowing instruction to try to prove
993 // non-wrapping for the *specific* value of Ptr.
994
995 // The arithmetic implied by an inbounds GEP can't overflow.
996 auto *GEP = dyn_cast<GetElementPtrInst>(Ptr);
997 if (!GEP || !GEP->isInBounds())
998 return false;
999
1000 // Make sure there is only one non-const index and analyze that.
1001 Value *NonConstIndex = nullptr;
1002 for (Value *Index : GEP->indices())
1003 if (!isa<ConstantInt>(Index)) {
1004 if (NonConstIndex)
1005 return false;
1006 NonConstIndex = Index;
1007 }
1008 if (!NonConstIndex)
1009 // The recurrence is on the pointer, ignore for now.
1010 return false;
1011
1012 // The index in GEP is signed. It is non-wrapping if it's derived from a NSW
1013 // AddRec using a NSW operation.
1014 if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(NonConstIndex))
1015 if (OBO->hasNoSignedWrap() &&
1016 // Assume constant for other the operand so that the AddRec can be
1017 // easily found.
1018 isa<ConstantInt>(OBO->getOperand(1))) {
1019 auto *OpScev = PSE.getSCEV(OBO->getOperand(0));
1020
1021 if (auto *OpAR = dyn_cast<SCEVAddRecExpr>(OpScev))
1022 return OpAR->getLoop() == L && OpAR->getNoWrapFlags(SCEV::FlagNSW);
1023 }
1024
1025 return false;
1026}
1027
1028/// Check whether the access through \p Ptr has a constant stride.
1029int64_t llvm::getPtrStride(PredicatedScalarEvolution &PSE, Value *Ptr,
1030 const Loop *Lp, const ValueToValueMap &StridesMap,
1031 bool Assume, bool ShouldCheckWrap) {
1032 Type *Ty = Ptr->getType();
1033 assert(Ty->isPointerTy() && "Unexpected non-ptr")((void)0);
1034
1035 // Make sure that the pointer does not point to aggregate types.
1036 auto *PtrTy = cast<PointerType>(Ty);
1037 if (PtrTy->getElementType()->isAggregateType()) {
1038 LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type"do { } while (false)
1039 << *Ptr << "\n")do { } while (false);
1040 return 0;
1041 }
1042
1043 const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr);
1044
1045 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
1046 if (Assume && !AR)
1047 AR = PSE.getAsAddRec(Ptr);
1048
1049 if (!AR) {
1050 LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer " << *Ptrdo { } while (false)
1051 << " SCEV: " << *PtrScev << "\n")do { } while (false);
1052 return 0;
1053 }
1054
1055 // The access function must stride over the innermost loop.
1056 if (Lp != AR->getLoop()) {
1057 LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop "do { } while (false)
1058 << *Ptr << " SCEV: " << *AR << "\n")do { } while (false);
1059 return 0;
1060 }
1061
1062 // The address calculation must not wrap. Otherwise, a dependence could be
1063 // inverted.
1064 // An inbounds getelementptr that is a AddRec with a unit stride
1065 // cannot wrap per definition. The unit stride requirement is checked later.
1066 // An getelementptr without an inbounds attribute and unit stride would have
1067 // to access the pointer value "0" which is undefined behavior in address
1068 // space 0, therefore we can also vectorize this case.
1069 bool IsInBoundsGEP = isInBoundsGep(Ptr);
1070 bool IsNoWrapAddRec = !ShouldCheckWrap ||
1071 PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW) ||
1072 isNoWrapAddRec(Ptr, AR, PSE, Lp);
1073 if (!IsNoWrapAddRec && !IsInBoundsGEP &&
1074 NullPointerIsDefined(Lp->getHeader()->getParent(),
1075 PtrTy->getAddressSpace())) {
1076 if (Assume) {
1077 PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW);
1078 IsNoWrapAddRec = true;
1079 LLVM_DEBUG(dbgs() << "LAA: Pointer may wrap in the address space:\n"do { } while (false)
1080 << "LAA: Pointer: " << *Ptr << "\n"do { } while (false)
1081 << "LAA: SCEV: " << *AR << "\n"do { } while (false)
1082 << "LAA: Added an overflow assumption\n")do { } while (false);
1083 } else {
1084 LLVM_DEBUG(do { } while (false)
1085 dbgs() << "LAA: Bad stride - Pointer may wrap in the address space "do { } while (false)
1086 << *Ptr << " SCEV: " << *AR << "\n")do { } while (false);
1087 return 0;
1088 }
1089 }
1090
1091 // Check the step is constant.
1092 const SCEV *Step = AR->getStepRecurrence(*PSE.getSE());
1093
1094 // Calculate the pointer stride and check if it is constant.
1095 const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
1096 if (!C) {
1097 LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptrdo { } while (false)
1098 << " SCEV: " << *AR << "\n")do { } while (false);
1099 return 0;
1100 }
1101
1102 auto &DL = Lp->getHeader()->getModule()->getDataLayout();
1103 int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType());
1104 const APInt &APStepVal = C->getAPInt();
1105
1106 // Huge step value - give up.
1107 if (APStepVal.getBitWidth() > 64)
1108 return 0;
1109
1110 int64_t StepVal = APStepVal.getSExtValue();
1111
1112 // Strided access.
1113 int64_t Stride = StepVal / Size;
1114 int64_t Rem = StepVal % Size;
1115 if (Rem)
1116 return 0;
1117
1118 // If the SCEV could wrap but we have an inbounds gep with a unit stride we
1119 // know we can't "wrap around the address space". In case of address space
1120 // zero we know that this won't happen without triggering undefined behavior.
1121 if (!IsNoWrapAddRec && Stride != 1 && Stride != -1 &&
1122 (IsInBoundsGEP || !NullPointerIsDefined(Lp->getHeader()->getParent(),
1123 PtrTy->getAddressSpace()))) {
1124 if (Assume) {
1125 // We can avoid this case by adding a run-time check.
1126 LLVM_DEBUG(dbgs() << "LAA: Non unit strided pointer which is not either "do { } while (false)
1127 << "inbounds or in address space 0 may wrap:\n"do { } while (false)
1128 << "LAA: Pointer: " << *Ptr << "\n"do { } while (false)
1129 << "LAA: SCEV: " << *AR << "\n"do { } while (false)
1130 << "LAA: Added an overflow assumption\n")do { } while (false);
1131 PSE.setNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW);
1132 } else
1133 return 0;
1134 }
1135
1136 return Stride;
1137}
1138
1139Optional<int> llvm::getPointersDiff(Type *ElemTyA, Value *PtrA, Type *ElemTyB,
1140 Value *PtrB, const DataLayout &DL,
1141 ScalarEvolution &SE, bool StrictCheck,
1142 bool CheckType) {
1143 assert(PtrA && PtrB && "Expected non-nullptr pointers.")((void)0);
1144 assert(cast<PointerType>(PtrA->getType())((void)0)
1145 ->isOpaqueOrPointeeTypeMatches(ElemTyA) && "Wrong PtrA type")((void)0);
1146 assert(cast<PointerType>(PtrB->getType())((void)0)
1147 ->isOpaqueOrPointeeTypeMatches(ElemTyB) && "Wrong PtrB type")((void)0);
1148
1149 // Make sure that A and B are different pointers.
1150 if (PtrA == PtrB)
1151 return 0;
1152
1153 // Make sure that the element types are the same if required.
1154 if (CheckType && ElemTyA != ElemTyB)
1155 return None;
1156
1157 unsigned ASA = PtrA->getType()->getPointerAddressSpace();
1158 unsigned ASB = PtrB->getType()->getPointerAddressSpace();
1159
1160 // Check that the address spaces match.
1161 if (ASA != ASB)
1162 return None;
1163 unsigned IdxWidth = DL.getIndexSizeInBits(ASA);
1164
1165 APInt OffsetA(IdxWidth, 0), OffsetB(IdxWidth, 0);
1166 Value *PtrA1 = PtrA->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetA);
1167 Value *PtrB1 = PtrB->stripAndAccumulateInBoundsConstantOffsets(DL, OffsetB);
1168
1169 int Val;
1170 if (PtrA1 == PtrB1) {
1171 // Retrieve the address space again as pointer stripping now tracks through
1172 // `addrspacecast`.
1173 ASA = cast<PointerType>(PtrA1->getType())->getAddressSpace();
1174 ASB = cast<PointerType>(PtrB1->getType())->getAddressSpace();
1175 // Check that the address spaces match and that the pointers are valid.
1176 if (ASA != ASB)
1177 return None;
1178
1179 IdxWidth = DL.getIndexSizeInBits(ASA);
1180 OffsetA = OffsetA.sextOrTrunc(IdxWidth);
1181 OffsetB = OffsetB.sextOrTrunc(IdxWidth);
1182
1183 OffsetB -= OffsetA;
1184 Val = OffsetB.getSExtValue();
1185 } else {
1186 // Otherwise compute the distance with SCEV between the base pointers.
1187 const SCEV *PtrSCEVA = SE.getSCEV(PtrA);
1188 const SCEV *PtrSCEVB = SE.getSCEV(PtrB);
1189 const auto *Diff =
1190 dyn_cast<SCEVConstant>(SE.getMinusSCEV(PtrSCEVB, PtrSCEVA));
1191 if (!Diff)
1192 return None;
1193 Val = Diff->getAPInt().getSExtValue();
1194 }
1195 int Size = DL.getTypeStoreSize(ElemTyA);
1196 int Dist = Val / Size;
1197
1198 // Ensure that the calculated distance matches the type-based one after all
1199 // the bitcasts removal in the provided pointers.
1200 if (!StrictCheck || Dist * Size == Val)
1201 return Dist;
1202 return None;
1203}
1204
1205bool llvm::sortPtrAccesses(ArrayRef<Value *> VL, Type *ElemTy,
1206 const DataLayout &DL, ScalarEvolution &SE,
1207 SmallVectorImpl<unsigned> &SortedIndices) {
1208 assert(llvm::all_of(((void)0)
1209 VL, [](const Value *V) { return V->getType()->isPointerTy(); }) &&((void)0)
1210 "Expected list of pointer operands.")((void)0);
1211 // Walk over the pointers, and map each of them to an offset relative to
1212 // first pointer in the array.
1213 Value *Ptr0 = VL[0];
1214
1215 using DistOrdPair = std::pair<int64_t, int>;
1216 auto Compare = [](const DistOrdPair &L, const DistOrdPair &R) {
1217 return L.first < R.first;
1218 };
1219 std::set<DistOrdPair, decltype(Compare)> Offsets(Compare);
1220 Offsets.emplace(0, 0);
1221 int Cnt = 1;
1222 bool IsConsecutive = true;
1223 for (auto *Ptr : VL.drop_front()) {
1224 Optional<int> Diff = getPointersDiff(ElemTy, Ptr0, ElemTy, Ptr, DL, SE,
1225 /*StrictCheck=*/true);
1226 if (!Diff)
1227 return false;
1228
1229 // Check if the pointer with the same offset is found.
1230 int64_t Offset = *Diff;
1231 auto Res = Offsets.emplace(Offset, Cnt);
1232 if (!Res.second)
1233 return false;
1234 // Consecutive order if the inserted element is the last one.
1235 IsConsecutive = IsConsecutive && std::next(Res.first) == Offsets.end();
1236 ++Cnt;
1237 }
1238 SortedIndices.clear();
1239 if (!IsConsecutive) {
1240 // Fill SortedIndices array only if it is non-consecutive.
1241 SortedIndices.resize(VL.size());
1242 Cnt = 0;
1243 for (const std::pair<int64_t, int> &Pair : Offsets) {
1244 SortedIndices[Cnt] = Pair.second;
1245 ++Cnt;
1246 }
1247 }
1248 return true;
1249}
1250
1251/// Returns true if the memory operations \p A and \p B are consecutive.
1252bool llvm::isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL,
1253 ScalarEvolution &SE, bool CheckType) {
1254 Value *PtrA = getLoadStorePointerOperand(A);
1255 Value *PtrB = getLoadStorePointerOperand(B);
1256 if (!PtrA || !PtrB)
1257 return false;
1258 Type *ElemTyA = getLoadStoreType(A);
1259 Type *ElemTyB = getLoadStoreType(B);
1260 Optional<int> Diff = getPointersDiff(ElemTyA, PtrA, ElemTyB, PtrB, DL, SE,
1261 /*StrictCheck=*/true, CheckType);
1262 return Diff && *Diff == 1;
1263}
1264
1265MemoryDepChecker::VectorizationSafetyStatus
1266MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) {
1267 switch (Type) {
1268 case NoDep:
1269 case Forward:
1270 case BackwardVectorizable:
1271 return VectorizationSafetyStatus::Safe;
1272
1273 case Unknown:
1274 return VectorizationSafetyStatus::PossiblySafeWithRtChecks;
1275 case ForwardButPreventsForwarding:
1276 case Backward:
1277 case BackwardVectorizableButPreventsForwarding:
1278 return VectorizationSafetyStatus::Unsafe;
1279 }
1280 llvm_unreachable("unexpected DepType!")__builtin_unreachable();
1281}
1282
1283bool MemoryDepChecker::Dependence::isBackward() const {
1284 switch (Type) {
1285 case NoDep:
1286 case Forward:
1287 case ForwardButPreventsForwarding:
1288 case Unknown:
1289 return false;
1290
1291 case BackwardVectorizable:
1292 case Backward:
1293 case BackwardVectorizableButPreventsForwarding:
1294 return true;
1295 }
1296 llvm_unreachable("unexpected DepType!")__builtin_unreachable();
1297}
1298
1299bool MemoryDepChecker::Dependence::isPossiblyBackward() const {
1300 return isBackward() || Type == Unknown;
1301}
1302
1303bool MemoryDepChecker::Dependence::isForward() const {
1304 switch (Type) {
1305 case Forward:
1306 case ForwardButPreventsForwarding:
1307 return true;
1308
1309 case NoDep:
1310 case Unknown:
1311 case BackwardVectorizable:
1312 case Backward:
1313 case BackwardVectorizableButPreventsForwarding:
1314 return false;
1315 }
1316 llvm_unreachable("unexpected DepType!")__builtin_unreachable();
1317}
1318
1319bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance,
1320 uint64_t TypeByteSize) {
1321 // If loads occur at a distance that is not a multiple of a feasible vector
1322 // factor store-load forwarding does not take place.
1323 // Positive dependences might cause troubles because vectorizing them might
1324 // prevent store-load forwarding making vectorized code run a lot slower.
1325 // a[i] = a[i-3] ^ a[i-8];
1326 // The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and
1327 // hence on your typical architecture store-load forwarding does not take
1328 // place. Vectorizing in such cases does not make sense.
1329 // Store-load forwarding distance.
1330
1331 // After this many iterations store-to-load forwarding conflicts should not
1332 // cause any slowdowns.
1333 const uint64_t NumItersForStoreLoadThroughMemory = 8 * TypeByteSize;
1334 // Maximum vector factor.
1335 uint64_t MaxVFWithoutSLForwardIssues = std::min(
1336 VectorizerParams::MaxVectorWidth * TypeByteSize, MaxSafeDepDistBytes);
1337
1338 // Compute the smallest VF at which the store and load would be misaligned.
1339 for (uint64_t VF = 2 * TypeByteSize; VF <= MaxVFWithoutSLForwardIssues;
1340 VF *= 2) {
1341 // If the number of vector iteration between the store and the load are
1342 // small we could incur conflicts.
1343 if (Distance % VF && Distance / VF < NumItersForStoreLoadThroughMemory) {
1344 MaxVFWithoutSLForwardIssues = (VF >> 1);
1345 break;
1346 }
1347 }
1348
1349 if (MaxVFWithoutSLForwardIssues < 2 * TypeByteSize) {
1350 LLVM_DEBUG(do { } while (false)
1351 dbgs() << "LAA: Distance " << Distancedo { } while (false)
1352 << " that could cause a store-load forwarding conflict\n")do { } while (false);
1353 return true;
1354 }
1355
1356 if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes &&
1357 MaxVFWithoutSLForwardIssues !=
1358 VectorizerParams::MaxVectorWidth * TypeByteSize)
1359 MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues;
1360 return false;
1361}
1362
1363void MemoryDepChecker::mergeInStatus(VectorizationSafetyStatus S) {
1364 if (Status < S)
1365 Status = S;
1366}
1367
1368/// Given a non-constant (unknown) dependence-distance \p Dist between two
1369/// memory accesses, that have the same stride whose absolute value is given
1370/// in \p Stride, and that have the same type size \p TypeByteSize,
1371/// in a loop whose takenCount is \p BackedgeTakenCount, check if it is
1372/// possible to prove statically that the dependence distance is larger
1373/// than the range that the accesses will travel through the execution of
1374/// the loop. If so, return true; false otherwise. This is useful for
1375/// example in loops such as the following (PR31098):
1376/// for (i = 0; i < D; ++i) {
1377/// = out[i];
1378/// out[i+D] =
1379/// }
1380static bool isSafeDependenceDistance(const DataLayout &DL, ScalarEvolution &SE,
1381 const SCEV &BackedgeTakenCount,
1382 const SCEV &Dist, uint64_t Stride,
1383 uint64_t TypeByteSize) {
1384
1385 // If we can prove that
1386 // (**) |Dist| > BackedgeTakenCount * Step
1387 // where Step is the absolute stride of the memory accesses in bytes,
1388 // then there is no dependence.
1389 //
1390 // Rationale:
1391 // We basically want to check if the absolute distance (|Dist/Step|)
1392 // is >= the loop iteration count (or > BackedgeTakenCount).
1393 // This is equivalent to the Strong SIV Test (Practical Dependence Testing,
1394 // Section 4.2.1); Note, that for vectorization it is sufficient to prove
1395 // that the dependence distance is >= VF; This is checked elsewhere.
1396 // But in some cases we can prune unknown dependence distances early, and
1397 // even before selecting the VF, and without a runtime test, by comparing
1398 // the distance against the loop iteration count. Since the vectorized code
1399 // will be executed only if LoopCount >= VF, proving distance >= LoopCount
1400 // also guarantees that distance >= VF.
1401 //
1402 const uint64_t ByteStride = Stride * TypeByteSize;
1403 const SCEV *Step = SE.getConstant(BackedgeTakenCount.getType(), ByteStride);
1404 const SCEV *Product = SE.getMulExpr(&BackedgeTakenCount, Step);
1405
1406 const SCEV *CastedDist = &Dist;
1407 const SCEV *CastedProduct = Product;
1408 uint64_t DistTypeSize = DL.getTypeAllocSize(Dist.getType());
1409 uint64_t ProductTypeSize = DL.getTypeAllocSize(Product->getType());
1410
1411 // The dependence distance can be positive/negative, so we sign extend Dist;
1412 // The multiplication of the absolute stride in bytes and the
1413 // backedgeTakenCount is non-negative, so we zero extend Product.
1414 if (DistTypeSize > ProductTypeSize)
1415 CastedProduct = SE.getZeroExtendExpr(Product, Dist.getType());
1416 else
1417 CastedDist = SE.getNoopOrSignExtend(&Dist, Product->getType());
1418
1419 // Is Dist - (BackedgeTakenCount * Step) > 0 ?
1420 // (If so, then we have proven (**) because |Dist| >= Dist)
1421 const SCEV *Minus = SE.getMinusSCEV(CastedDist, CastedProduct);
1422 if (SE.isKnownPositive(Minus))
1423 return true;
1424
1425 // Second try: Is -Dist - (BackedgeTakenCount * Step) > 0 ?
1426 // (If so, then we have proven (**) because |Dist| >= -1*Dist)
1427 const SCEV *NegDist = SE.getNegativeSCEV(CastedDist);
1428 Minus = SE.getMinusSCEV(NegDist, CastedProduct);
1429 if (SE.isKnownPositive(Minus))
1430 return true;
1431
1432 return false;
1433}
1434
1435/// Check the dependence for two accesses with the same stride \p Stride.
1436/// \p Distance is the positive distance and \p TypeByteSize is type size in
1437/// bytes.
1438///
1439/// \returns true if they are independent.
1440static bool areStridedAccessesIndependent(uint64_t Distance, uint64_t Stride,
1441 uint64_t TypeByteSize) {
1442 assert(Stride > 1 && "The stride must be greater than 1")((void)0);
1443 assert(TypeByteSize > 0 && "The type size in byte must be non-zero")((void)0);
1444 assert(Distance > 0 && "The distance must be non-zero")((void)0);
1445
1446 // Skip if the distance is not multiple of type byte size.
1447 if (Distance % TypeByteSize)
1448 return false;
1449
1450 uint64_t ScaledDist = Distance / TypeByteSize;
1451
1452 // No dependence if the scaled distance is not multiple of the stride.
1453 // E.g.
1454 // for (i = 0; i < 1024 ; i += 4)
1455 // A[i+2] = A[i] + 1;
1456 //
1457 // Two accesses in memory (scaled distance is 2, stride is 4):
1458 // | A[0] | | | | A[4] | | | |
1459 // | | | A[2] | | | | A[6] | |
1460 //
1461 // E.g.
1462 // for (i = 0; i < 1024 ; i += 3)
1463 // A[i+4] = A[i] + 1;
1464 //
1465 // Two accesses in memory (scaled distance is 4, stride is 3):
1466 // | A[0] | | | A[3] | | | A[6] | | |
1467 // | | | | | A[4] | | | A[7] | |
1468 return ScaledDist % Stride;
1469}
1470
1471MemoryDepChecker::Dependence::DepType
1472MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
1473 const MemAccessInfo &B, unsigned BIdx,
1474 const ValueToValueMap &Strides) {
1475 assert (AIdx < BIdx && "Must pass arguments in program order")((void)0);
1476
1477 Value *APtr = A.getPointer();
1478 Value *BPtr = B.getPointer();
1479 bool AIsWrite = A.getInt();
1480 bool BIsWrite = B.getInt();
1481
1482 // Two reads are independent.
1483 if (!AIsWrite && !BIsWrite)
1484 return Dependence::NoDep;
1485
1486 // We cannot check pointers in different address spaces.
1487 if (APtr->getType()->getPointerAddressSpace() !=
1488 BPtr->getType()->getPointerAddressSpace())
1489 return Dependence::Unknown;
1490
1491 int64_t StrideAPtr = getPtrStride(PSE, APtr, InnermostLoop, Strides, true);
1492 int64_t StrideBPtr = getPtrStride(PSE, BPtr, InnermostLoop, Strides, true);
1493
1494 const SCEV *Src = PSE.getSCEV(APtr);
1495 const SCEV *Sink = PSE.getSCEV(BPtr);
1496
1497 // If the induction step is negative we have to invert source and sink of the
1498 // dependence.
1499 if (StrideAPtr < 0) {
1500 std::swap(APtr, BPtr);
1501 std::swap(Src, Sink);
1502 std::swap(AIsWrite, BIsWrite);
1503 std::swap(AIdx, BIdx);
1504 std::swap(StrideAPtr, StrideBPtr);
1505 }
1506
1507 const SCEV *Dist = PSE.getSE()->getMinusSCEV(Sink, Src);
1508
1509 LLVM_DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sinkdo { } while (false)
1510 << "(Induction step: " << StrideAPtr << ")\n")do { } while (false);
1511 LLVM_DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to "do { } while (false)
1512 << *InstMap[BIdx] << ": " << *Dist << "\n")do { } while (false);
1513
1514 // Need accesses with constant stride. We don't want to vectorize
1515 // "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in
1516 // the address space.
1517 if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){
1518 LLVM_DEBUG(dbgs() << "Pointer access with non-constant stride\n")do { } while (false);
1519 return Dependence::Unknown;
1520 }
1521
1522 Type *ATy = APtr->getType()->getPointerElementType();
1523 Type *BTy = BPtr->getType()->getPointerElementType();
1524 auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
1525 uint64_t TypeByteSize = DL.getTypeAllocSize(ATy);
1526 uint64_t Stride = std::abs(StrideAPtr);
1527 const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
1528 if (!C) {
1529 if (!isa<SCEVCouldNotCompute>(Dist) &&
1530 TypeByteSize == DL.getTypeAllocSize(BTy) &&
1531 isSafeDependenceDistance(DL, *(PSE.getSE()),
1532 *(PSE.getBackedgeTakenCount()), *Dist, Stride,
1533 TypeByteSize))
1534 return Dependence::NoDep;
1535
1536 LLVM_DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n")do { } while (false);
1537 FoundNonConstantDistanceDependence = true;
1538 return Dependence::Unknown;
1539 }
1540
1541 const APInt &Val = C->getAPInt();
1542 int64_t Distance = Val.getSExtValue();
1543
1544 // Attempt to prove strided accesses independent.
1545 if (std::abs(Distance) > 0 && Stride > 1 && ATy == BTy &&
1546 areStridedAccessesIndependent(std::abs(Distance), Stride, TypeByteSize)) {
1547 LLVM_DEBUG(dbgs() << "LAA: Strided accesses are independent\n")do { } while (false);
1548 return Dependence::NoDep;
1549 }
1550
1551 // Negative distances are not plausible dependencies.
1552 if (Val.isNegative()) {
1553 bool IsTrueDataDependence = (AIsWrite && !BIsWrite);
1554 if (IsTrueDataDependence && EnableForwardingConflictDetection &&
1555 (couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) ||
1556 ATy != BTy)) {
1557 LLVM_DEBUG(dbgs() << "LAA: Forward but may prevent st->ld forwarding\n")do { } while (false);
1558 return Dependence::ForwardButPreventsForwarding;
1559 }
1560
1561 LLVM_DEBUG(dbgs() << "LAA: Dependence is negative\n")do { } while (false);
1562 return Dependence::Forward;
1563 }
1564
1565 // Write to the same location with the same size.
1566 // Could be improved to assert type sizes are the same (i32 == float, etc).
1567 if (Val == 0) {
1568 if (ATy == BTy)
1569 return Dependence::Forward;
1570 LLVM_DEBUG(do { } while (false)
1571 dbgs() << "LAA: Zero dependence difference but different types\n")do { } while (false);
1572 return Dependence::Unknown;
1573 }
1574
1575 assert(Val.isStrictlyPositive() && "Expect a positive value")((void)0);
1576
1577 if (ATy != BTy) {
1578 LLVM_DEBUG(do { } while (false)
1579 dbgs()do { } while (false)
1580 << "LAA: ReadWrite-Write positive dependency with different types\n")do { } while (false);
1581 return Dependence::Unknown;
1582 }
1583
1584 // Bail out early if passed-in parameters make vectorization not feasible.
1585 unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ?
1586 VectorizerParams::VectorizationFactor : 1);
1587 unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ?
1588 VectorizerParams::VectorizationInterleave : 1);
1589 // The minimum number of iterations for a vectorized/unrolled version.
1590 unsigned MinNumIter = std::max(ForcedFactor * ForcedUnroll, 2U);
1591
1592 // It's not vectorizable if the distance is smaller than the minimum distance
1593 // needed for a vectroized/unrolled version. Vectorizing one iteration in
1594 // front needs TypeByteSize * Stride. Vectorizing the last iteration needs
1595 // TypeByteSize (No need to plus the last gap distance).
1596 //
1597 // E.g. Assume one char is 1 byte in memory and one int is 4 bytes.
1598 // foo(int *A) {
1599 // int *B = (int *)((char *)A + 14);
1600 // for (i = 0 ; i < 1024 ; i += 2)
1601 // B[i] = A[i] + 1;
1602 // }
1603 //
1604 // Two accesses in memory (stride is 2):
1605 // | A[0] | | A[2] | | A[4] | | A[6] | |
1606 // | B[0] | | B[2] | | B[4] |
1607 //
1608 // Distance needs for vectorizing iterations except the last iteration:
1609 // 4 * 2 * (MinNumIter - 1). Distance needs for the last iteration: 4.
1610 // So the minimum distance needed is: 4 * 2 * (MinNumIter - 1) + 4.
1611 //
1612 // If MinNumIter is 2, it is vectorizable as the minimum distance needed is
1613 // 12, which is less than distance.
1614 //
1615 // If MinNumIter is 4 (Say if a user forces the vectorization factor to be 4),
1616 // the minimum distance needed is 28, which is greater than distance. It is
1617 // not safe to do vectorization.
1618 uint64_t MinDistanceNeeded =
1619 TypeByteSize * Stride * (MinNumIter - 1) + TypeByteSize;
1620 if (MinDistanceNeeded > static_cast<uint64_t>(Distance)) {
1621 LLVM_DEBUG(dbgs() << "LAA: Failure because of positive distance "do { } while (false)
1622 << Distance << '\n')do { } while (false);
1623 return Dependence::Backward;
1624 }
1625
1626 // Unsafe if the minimum distance needed is greater than max safe distance.
1627 if (MinDistanceNeeded > MaxSafeDepDistBytes) {
1628 LLVM_DEBUG(dbgs() << "LAA: Failure because it needs at least "do { } while (false)
1629 << MinDistanceNeeded << " size in bytes")do { } while (false);
1630 return Dependence::Backward;
1631 }
1632
1633 // Positive distance bigger than max vectorization factor.
1634 // FIXME: Should use max factor instead of max distance in bytes, which could
1635 // not handle different types.
1636 // E.g. Assume one char is 1 byte in memory and one int is 4 bytes.
1637 // void foo (int *A, char *B) {
1638 // for (unsigned i = 0; i < 1024; i++) {
1639 // A[i+2] = A[i] + 1;
1640 // B[i+2] = B[i] + 1;
1641 // }
1642 // }
1643 //
1644 // This case is currently unsafe according to the max safe distance. If we
1645 // analyze the two accesses on array B, the max safe dependence distance
1646 // is 2. Then we analyze the accesses on array A, the minimum distance needed
1647 // is 8, which is less than 2 and forbidden vectorization, But actually
1648 // both A and B could be vectorized by 2 iterations.
1649 MaxSafeDepDistBytes =
1650 std::min(static_cast<uint64_t>(Distance), MaxSafeDepDistBytes);
1651
1652 bool IsTrueDataDependence = (!AIsWrite && BIsWrite);
1653 if (IsTrueDataDependence && EnableForwardingConflictDetection &&
1654 couldPreventStoreLoadForward(Distance, TypeByteSize))
1655 return Dependence::BackwardVectorizableButPreventsForwarding;
1656
1657 uint64_t MaxVF = MaxSafeDepDistBytes / (TypeByteSize * Stride);
1658 LLVM_DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue()do { } while (false)
1659 << " with max VF = " << MaxVF << '\n')do { } while (false);
1660 uint64_t MaxVFInBits = MaxVF * TypeByteSize * 8;
1661 MaxSafeVectorWidthInBits = std::min(MaxSafeVectorWidthInBits, MaxVFInBits);
1662 return Dependence::BackwardVectorizable;
1663}
1664
1665bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
1666 MemAccessInfoList &CheckDeps,
1667 const ValueToValueMap &Strides) {
1668
1669 MaxSafeDepDistBytes = -1;
1670 SmallPtrSet<MemAccessInfo, 8> Visited;
1671 for (MemAccessInfo CurAccess : CheckDeps) {
1672 if (Visited.count(CurAccess))
1673 continue;
1674
1675 // Get the relevant memory access set.
1676 EquivalenceClasses<MemAccessInfo>::iterator I =
1677 AccessSets.findValue(AccessSets.getLeaderValue(CurAccess));
1678
1679 // Check accesses within this set.
1680 EquivalenceClasses<MemAccessInfo>::member_iterator AI =
1681 AccessSets.member_begin(I);
1682 EquivalenceClasses<MemAccessInfo>::member_iterator AE =
1683 AccessSets.member_end();
1684
1685 // Check every access pair.
1686 while (AI != AE) {
1687 Visited.insert(*AI);
1688 bool AIIsWrite = AI->getInt();
1689 // Check loads only against next equivalent class, but stores also against
1690 // other stores in the same equivalence class - to the same address.
1691 EquivalenceClasses<MemAccessInfo>::member_iterator OI =
1692 (AIIsWrite ? AI : std::next(AI));
1693 while (OI != AE) {
1694 // Check every accessing instruction pair in program order.
1695 for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(),
1696 I1E = Accesses[*AI].end(); I1 != I1E; ++I1)
1697 // Scan all accesses of another equivalence class, but only the next
1698 // accesses of the same equivalent class.
1699 for (std::vector<unsigned>::iterator
1700 I2 = (OI == AI ? std::next(I1) : Accesses[*OI].begin()),
1701 I2E = (OI == AI ? I1E : Accesses[*OI].end());
1702 I2 != I2E; ++I2) {
1703 auto A = std::make_pair(&*AI, *I1);
1704 auto B = std::make_pair(&*OI, *I2);
1705
1706 assert(*I1 != *I2)((void)0);
1707 if (*I1 > *I2)
1708 std::swap(A, B);
1709
1710 Dependence::DepType Type =
1711 isDependent(*A.first, A.second, *B.first, B.second, Strides);
1712 mergeInStatus(Dependence::isSafeForVectorization(Type));
1713
1714 // Gather dependences unless we accumulated MaxDependences
1715 // dependences. In that case return as soon as we find the first
1716 // unsafe dependence. This puts a limit on this quadratic
1717 // algorithm.
1718 if (RecordDependences) {
1719 if (Type != Dependence::NoDep)
1720 Dependences.push_back(Dependence(A.second, B.second, Type));
1721
1722 if (Dependences.size() >= MaxDependences) {
1723 RecordDependences = false;
1724 Dependences.clear();
1725 LLVM_DEBUG(dbgs()do { } while (false)
1726 << "Too many dependences, stopped recording\n")do { } while (false);
1727 }
1728 }
1729 if (!RecordDependences && !isSafeForVectorization())
1730 return false;
1731 }
1732 ++OI;
1733 }
1734 AI++;
1735 }
1736 }
1737
1738 LLVM_DEBUG(dbgs() << "Total Dependences: " << Dependences.size() << "\n")do { } while (false);
1739 return isSafeForVectorization();
1740}
1741
1742SmallVector<Instruction *, 4>
1743MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const {
1744 MemAccessInfo Access(Ptr, isWrite);
1745 auto &IndexVector = Accesses.find(Access)->second;
1746
1747 SmallVector<Instruction *, 4> Insts;
1748 transform(IndexVector,
1749 std::back_inserter(Insts),
1750 [&](unsigned Idx) { return this->InstMap[Idx]; });
1751 return Insts;
1752}
1753
1754const char *MemoryDepChecker::Dependence::DepName[] = {
1755 "NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward",
1756 "BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"};
1757
1758void MemoryDepChecker::Dependence::print(
1759 raw_ostream &OS, unsigned Depth,
1760 const SmallVectorImpl<Instruction *> &Instrs) const {
1761 OS.indent(Depth) << DepName[Type] << ":\n";
1762 OS.indent(Depth + 2) << *Instrs[Source] << " -> \n";
1763 OS.indent(Depth + 2) << *Instrs[Destination] << "\n";
1764}
1765
1766bool LoopAccessInfo::canAnalyzeLoop() {
1767 // We need to have a loop header.
1768 LLVM_DEBUG(dbgs() << "LAA: Found a loop in "do { } while (false)
1769 << TheLoop->getHeader()->getParent()->getName() << ": "do { } while (false)
1770 << TheLoop->getHeader()->getName() << '\n')do { } while (false);
1771
1772 // We can only analyze innermost loops.
1773 if (!TheLoop->isInnermost()) {
1774 LLVM_DEBUG(dbgs() << "LAA: loop is not the innermost loop\n")do { } while (false);
1775 recordAnalysis("NotInnerMostLoop") << "loop is not the innermost loop";
1776 return false;
1777 }
1778
1779 // We must have a single backedge.
1780 if (TheLoop->getNumBackEdges() != 1) {
1781 LLVM_DEBUG(do { } while (false)
1782 dbgs() << "LAA: loop control flow is not understood by analyzer\n")do { } while (false);
1783 recordAnalysis("CFGNotUnderstood")
1784 << "loop control flow is not understood by analyzer";
1785 return false;
1786 }
1787
1788 // ScalarEvolution needs to be able to find the exit count.
1789 const SCEV *ExitCount = PSE->getBackedgeTakenCount();
1790 if (isa<SCEVCouldNotCompute>(ExitCount)) {
1791 recordAnalysis("CantComputeNumberOfIterations")
1792 << "could not determine number of loop iterations";
1793 LLVM_DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n")do { } while (false);
1794 return false;
1795 }
1796
1797 return true;
1798}
1799
1800void LoopAccessInfo::analyzeLoop(AAResults *AA, LoopInfo *LI,
1801 const TargetLibraryInfo *TLI,
1802 DominatorTree *DT) {
1803 typedef SmallPtrSet<Value*, 16> ValueSet;
1804
1805 // Holds the Load and Store instructions.
1806 SmallVector<LoadInst *, 16> Loads;
1807 SmallVector<StoreInst *, 16> Stores;
1808
1809 // Holds all the different accesses in the loop.
1810 unsigned NumReads = 0;
1811 unsigned NumReadWrites = 0;
1812
1813 bool HasComplexMemInst = false;
1814
1815 // A runtime check is only legal to insert if there are no convergent calls.
1816 HasConvergentOp = false;
1817
1818 PtrRtChecking->Pointers.clear();
1819 PtrRtChecking->Need = false;
1820
1821 const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel();
1822
1823 const bool EnableMemAccessVersioningOfLoop =
1824 EnableMemAccessVersioning &&
1
Assuming the condition is false
1825 !TheLoop->getHeader()->getParent()->hasOptSize();
1826
1827 // For each block.
1828 for (BasicBlock *BB : TheLoop->blocks()) {
2
Assuming '__begin1' is equal to '__end1'
1829 // Scan the BB and collect legal loads and stores. Also detect any
1830 // convergent instructions.
1831 for (Instruction &I : *BB) {
1832 if (auto *Call = dyn_cast<CallBase>(&I)) {
1833 if (Call->isConvergent())
1834 HasConvergentOp = true;
1835 }
1836
1837 // With both a non-vectorizable memory instruction and a convergent
1838 // operation, found in this loop, no reason to continue the search.
1839 if (HasComplexMemInst && HasConvergentOp) {
1840 CanVecMem = false;
1841 return;
1842 }
1843
1844 // Avoid hitting recordAnalysis multiple times.
1845 if (HasComplexMemInst)
1846 continue;
1847
1848 // If this is a load, save it. If this instruction can read from memory
1849 // but is not a load, then we quit. Notice that we don't handle function
1850 // calls that read or write.
1851 if (I.mayReadFromMemory()) {
1852 // Many math library functions read the rounding mode. We will only
1853 // vectorize a loop if it contains known function calls that don't set
1854 // the flag. Therefore, it is safe to ignore this read from memory.
1855 auto *Call = dyn_cast<CallInst>(&I);
1856 if (Call && getVectorIntrinsicIDForCall(Call, TLI))
1857 continue;
1858
1859 // If the function has an explicit vectorized counterpart, we can safely
1860 // assume that it can be vectorized.
1861 if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() &&
1862 !VFDatabase::getMappings(*Call).empty())
1863 continue;
1864
1865 auto *Ld = dyn_cast<LoadInst>(&I);
1866 if (!Ld) {
1867 recordAnalysis("CantVectorizeInstruction", Ld)
1868 << "instruction cannot be vectorized";
1869 HasComplexMemInst = true;
1870 continue;
1871 }
1872 if (!Ld->isSimple() && !IsAnnotatedParallel) {
1873 recordAnalysis("NonSimpleLoad", Ld)
1874 << "read with atomic ordering or volatile read";
1875 LLVM_DEBUG(dbgs() << "LAA: Found a non-simple load.\n")do { } while (false);
1876 HasComplexMemInst = true;
1877 continue;
1878 }
1879 NumLoads++;
1880 Loads.push_back(Ld);
1881 DepChecker->addAccess(Ld);
1882 if (EnableMemAccessVersioningOfLoop)
1883 collectStridedAccess(Ld);
1884 continue;
1885 }
1886
1887 // Save 'store' instructions. Abort if other instructions write to memory.
1888 if (I.mayWriteToMemory()) {
1889 auto *St = dyn_cast<StoreInst>(&I);
1890 if (!St) {
1891 recordAnalysis("CantVectorizeInstruction", St)
1892 << "instruction cannot be vectorized";
1893 HasComplexMemInst = true;
1894 continue;
1895 }
1896 if (!St->isSimple() && !IsAnnotatedParallel) {
1897 recordAnalysis("NonSimpleStore", St)
1898 << "write with atomic ordering or volatile write";
1899 LLVM_DEBUG(dbgs() << "LAA: Found a non-simple store.\n")do { } while (false);
1900 HasComplexMemInst = true;
1901 continue;
1902 }
1903 NumStores++;
1904 Stores.push_back(St);
1905 DepChecker->addAccess(St);
1906 if (EnableMemAccessVersioningOfLoop)
1907 collectStridedAccess(St);
1908 }
1909 } // Next instr.
1910 } // Next block.
1911
1912 if (HasComplexMemInst
2.1
'HasComplexMemInst' is false
) {
3
Taking false branch
1913 CanVecMem = false;
1914 return;
1915 }
1916
1917 // Now we have two lists that hold the loads and the stores.
1918 // Next, we find the pointers that they use.
1919
1920 // Check if we see any stores. If there are no stores, then we don't
1921 // care if the pointers are *restrict*.
1922 if (!Stores.size()) {
4
Assuming the condition is false
5
Taking false branch
1923 LLVM_DEBUG(dbgs() << "LAA: Found a read-only loop!\n")do { } while (false);
1924 CanVecMem = true;
1925 return;
1926 }
1927
1928 MemoryDepChecker::DepCandidates DependentAccesses;
1929 AccessAnalysis Accesses(TheLoop, AA, LI, DependentAccesses, *PSE);
1930
1931 // Holds the analyzed pointers. We don't want to call getUnderlyingObjects
1932 // multiple times on the same object. If the ptr is accessed twice, once
1933 // for read and once for write, it will only appear once (on the write
1934 // list). This is okay, since we are going to check for conflicts between
1935 // writes and between reads and writes, but not between reads and reads.
1936 ValueSet Seen;
1937
1938 // Record uniform store addresses to identify if we have multiple stores
1939 // to the same address.
1940 ValueSet UniformStores;
1941
1942 for (StoreInst *ST : Stores) {
6
Assuming '__begin1' is equal to '__end1'
1943 Value *Ptr = ST->getPointerOperand();
1944
1945 if (isUniform(Ptr))
1946 HasDependenceInvolvingLoopInvariantAddress |=
1947 !UniformStores.insert(Ptr).second;
1948
1949 // If we did *not* see this pointer before, insert it to the read-write
1950 // list. At this phase it is only a 'write' list.
1951 if (Seen.insert(Ptr).second) {
1952 ++NumReadWrites;
1953
1954 MemoryLocation Loc = MemoryLocation::get(ST);
1955 // The TBAA metadata could have a control dependency on the predication
1956 // condition, so we cannot rely on it when determining whether or not we
1957 // need runtime pointer checks.
1958 if (blockNeedsPredication(ST->getParent(), TheLoop, DT))
1959 Loc.AATags.TBAA = nullptr;
1960
1961 Accesses.addStore(Loc);
1962 }
1963 }
1964
1965 if (IsAnnotatedParallel) {
7
Assuming 'IsAnnotatedParallel' is false
8
Taking false branch
1966 LLVM_DEBUG(do { } while (false)
1967 dbgs() << "LAA: A loop annotated parallel, ignore memory dependency "do { } while (false)
1968 << "checks.\n")do { } while (false);
1969 CanVecMem = true;
1970 return;
1971 }
1972
1973 for (LoadInst *LD : Loads) {
9
Assuming '__begin1' is equal to '__end1'
1974 Value *Ptr = LD->getPointerOperand();
1975 // If we did *not* see this pointer before, insert it to the
1976 // read list. If we *did* see it before, then it is already in
1977 // the read-write list. This allows us to vectorize expressions
1978 // such as A[i] += x; Because the address of A[i] is a read-write
1979 // pointer. This only works if the index of A[i] is consecutive.
1980 // If the address of i is unknown (for example A[B[i]]) then we may
1981 // read a few words, modify, and write a few words, and some of the
1982 // words may be written to the same address.
1983 bool IsReadOnlyPtr = false;
1984 if (Seen.insert(Ptr).second ||
1985 !getPtrStride(*PSE, Ptr, TheLoop, SymbolicStrides)) {
1986 ++NumReads;
1987 IsReadOnlyPtr = true;
1988 }
1989
1990 // See if there is an unsafe dependency between a load to a uniform address and
1991 // store to the same uniform address.
1992 if (UniformStores.count(Ptr)) {
1993 LLVM_DEBUG(dbgs() << "LAA: Found an unsafe dependency between a uniform "do { } while (false)
1994 "load and uniform store to the same address!\n")do { } while (false);
1995 HasDependenceInvolvingLoopInvariantAddress = true;
1996 }
1997
1998 MemoryLocation Loc = MemoryLocation::get(LD);
1999 // The TBAA metadata could have a control dependency on the predication
2000 // condition, so we cannot rely on it when determining whether or not we
2001 // need runtime pointer checks.
2002 if (blockNeedsPredication(LD->getParent(), TheLoop, DT))
2003 Loc.AATags.TBAA = nullptr;
2004
2005 Accesses.addLoad(Loc, IsReadOnlyPtr);
2006 }
2007
2008 // If we write (or read-write) to a single destination and there are no
2009 // other reads in this loop then is it safe to vectorize.
2010 if (NumReadWrites
9.1
'NumReadWrites' is not equal to 1
== 1 && NumReads == 0) {
2011 LLVM_DEBUG(dbgs() << "LAA: Found a write-only loop!\n")do { } while (false);
2012 CanVecMem = true;
2013 return;
2014 }
2015
2016 // Build dependence sets and check whether we need a runtime pointer bounds
2017 // check.
2018 Accesses.buildDependenceSets();
2019
2020 // Find pointers with computable bounds. We are going to use this information
2021 // to place a runtime bound check.
2022 bool CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE->getSE(),
10
Calling 'AccessAnalysis::canCheckPtrAtRT'
2023 TheLoop, SymbolicStrides);
2024 if (!CanDoRTIfNeeded) {
2025 recordAnalysis("CantIdentifyArrayBounds") << "cannot identify array bounds";
2026 LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because we can't find "do { } while (false)
2027 << "the array bounds.\n")do { } while (false);
2028 CanVecMem = false;
2029 return;
2030 }
2031
2032 LLVM_DEBUG(do { } while (false)
2033 dbgs() << "LAA: May be able to perform a memory runtime check if needed.\n")do { } while (false);
2034
2035 CanVecMem = true;
2036 if (Accesses.isDependencyCheckNeeded()) {
2037 LLVM_DEBUG(dbgs() << "LAA: Checking memory dependencies\n")do { } while (false);
2038 CanVecMem = DepChecker->areDepsSafe(
2039 DependentAccesses, Accesses.getDependenciesToCheck(), SymbolicStrides);
2040 MaxSafeDepDistBytes = DepChecker->getMaxSafeDepDistBytes();
2041
2042 if (!CanVecMem && DepChecker->shouldRetryWithRuntimeCheck()) {
2043 LLVM_DEBUG(dbgs() << "LAA: Retrying with memory checks\n")do { } while (false);
2044
2045 // Clear the dependency checks. We assume they are not needed.
2046 Accesses.resetDepChecks(*DepChecker);
2047
2048 PtrRtChecking->reset();
2049 PtrRtChecking->Need = true;
2050
2051 auto *SE = PSE->getSE();
2052 CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, SE, TheLoop,
2053 SymbolicStrides, true);
2054
2055 // Check that we found the bounds for the pointer.
2056 if (!CanDoRTIfNeeded) {
2057 recordAnalysis("CantCheckMemDepsAtRunTime")
2058 << "cannot check memory dependencies at runtime";
2059 LLVM_DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n")do { } while (false);
2060 CanVecMem = false;
2061 return;
2062 }
2063
2064 CanVecMem = true;
2065 }
2066 }
2067
2068 if (HasConvergentOp) {
2069 recordAnalysis("CantInsertRuntimeCheckWithConvergent")
2070 << "cannot add control dependency to convergent operation";
2071 LLVM_DEBUG(dbgs() << "LAA: We can't vectorize because a runtime check "do { } while (false)
2072 "would be needed with a convergent operation\n")do { } while (false);
2073 CanVecMem = false;
2074 return;
2075 }
2076
2077 if (CanVecMem)
2078 LLVM_DEBUG(do { } while (false)
2079 dbgs() << "LAA: No unsafe dependent memory operations in loop. We"do { } while (false)
2080 << (PtrRtChecking->Need ? "" : " don't")do { } while (false)
2081 << " need runtime memory checks.\n")do { } while (false);
2082 else {
2083 recordAnalysis("UnsafeMemDep")
2084 << "unsafe dependent memory operations in loop. Use "
2085 "#pragma loop distribute(enable) to allow loop distribution "
2086 "to attempt to isolate the offending operations into a separate "
2087 "loop";
2088 LLVM_DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n")do { } while (false);
2089 }
2090}
2091
2092bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
2093 DominatorTree *DT) {
2094 assert(TheLoop->contains(BB) && "Unknown block used")((void)0);
2095
2096 // Blocks that do not dominate the latch need predication.
2097 BasicBlock* Latch = TheLoop->getLoopLatch();
2098 return !DT->dominates(BB, Latch);
2099}
2100
2101OptimizationRemarkAnalysis &LoopAccessInfo::recordAnalysis(StringRef RemarkName,
2102 Instruction *I) {
2103 assert(!Report && "Multiple reports generated")((void)0);
2104
2105 Value *CodeRegion = TheLoop->getHeader();
2106 DebugLoc DL = TheLoop->getStartLoc();
2107
2108 if (I) {
2109 CodeRegion = I->getParent();
2110 // If there is no debug location attached to the instruction, revert back to
2111 // using the loop's.
2112 if (I->getDebugLoc())
2113 DL = I->getDebugLoc();
2114 }
2115
2116 Report = std::make_unique<OptimizationRemarkAnalysis>(DEBUG_TYPE"loop-accesses", RemarkName, DL,
2117 CodeRegion);
2118 return *Report;
2119}
2120
2121bool LoopAccessInfo::isUniform(Value *V) const {
2122 auto *SE = PSE->getSE();
2123 // Since we rely on SCEV for uniformity, if the type is not SCEVable, it is
2124 // never considered uniform.
2125 // TODO: Is this really what we want? Even without FP SCEV, we may want some
2126 // trivially loop-invariant FP values to be considered uniform.
2127 if (!SE->isSCEVable(V->getType()))
2128 return false;
2129 return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop));
2130}
2131
2132void LoopAccessInfo::collectStridedAccess(Value *MemAccess) {
2133 Value *Ptr = getLoadStorePointerOperand(MemAccess);
2134 if (!Ptr)
2135 return;
2136
2137 Value *Stride = getStrideFromPointer(Ptr, PSE->getSE(), TheLoop);
2138 if (!Stride)
2139 return;
2140
2141 LLVM_DEBUG(dbgs() << "LAA: Found a strided access that is a candidate for "do { } while (false)
2142 "versioning:")do { } while (false);
2143 LLVM_DEBUG(dbgs() << " Ptr: " << *Ptr << " Stride: " << *Stride << "\n")do { } while (false);
2144
2145 // Avoid adding the "Stride == 1" predicate when we know that
2146 // Stride >= Trip-Count. Such a predicate will effectively optimize a single
2147 // or zero iteration loop, as Trip-Count <= Stride == 1.
2148 //
2149 // TODO: We are currently not making a very informed decision on when it is
2150 // beneficial to apply stride versioning. It might make more sense that the
2151 // users of this analysis (such as the vectorizer) will trigger it, based on
2152 // their specific cost considerations; For example, in cases where stride
2153 // versioning does not help resolving memory accesses/dependences, the
2154 // vectorizer should evaluate the cost of the runtime test, and the benefit
2155 // of various possible stride specializations, considering the alternatives
2156 // of using gather/scatters (if available).
2157
2158 const SCEV *StrideExpr = PSE->getSCEV(Stride);
2159 const SCEV *BETakenCount = PSE->getBackedgeTakenCount();
2160
2161 // Match the types so we can compare the stride and the BETakenCount.
2162 // The Stride can be positive/negative, so we sign extend Stride;
2163 // The backedgeTakenCount is non-negative, so we zero extend BETakenCount.
2164 const DataLayout &DL = TheLoop->getHeader()->getModule()->getDataLayout();
2165 uint64_t StrideTypeSize = DL.getTypeAllocSize(StrideExpr->getType());
2166 uint64_t BETypeSize = DL.getTypeAllocSize(BETakenCount->getType());
2167 const SCEV *CastedStride = StrideExpr;
2168 const SCEV *CastedBECount = BETakenCount;
2169 ScalarEvolution *SE = PSE->getSE();
2170 if (BETypeSize >= StrideTypeSize)
2171 CastedStride = SE->getNoopOrSignExtend(StrideExpr, BETakenCount->getType());
2172 else
2173 CastedBECount = SE->getZeroExtendExpr(BETakenCount, StrideExpr->getType());
2174 const SCEV *StrideMinusBETaken = SE->getMinusSCEV(CastedStride, CastedBECount);
2175 // Since TripCount == BackEdgeTakenCount + 1, checking:
2176 // "Stride >= TripCount" is equivalent to checking:
2177 // Stride - BETakenCount > 0
2178 if (SE->isKnownPositive(StrideMinusBETaken)) {
2179 LLVM_DEBUG(do { } while (false)
2180 dbgs() << "LAA: Stride>=TripCount; No point in versioning as the "do { } while (false)
2181 "Stride==1 predicate will imply that the loop executes "do { } while (false)
2182 "at most once.\n")do { } while (false);
2183 return;
2184 }
2185 LLVM_DEBUG(dbgs() << "LAA: Found a strided access that we can version.")do { } while (false);
2186
2187 SymbolicStrides[Ptr] = Stride;
2188 StrideSet.insert(Stride);
2189}
2190
2191LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
2192 const TargetLibraryInfo *TLI, AAResults *AA,
2193 DominatorTree *DT, LoopInfo *LI)
2194 : PSE(std::make_unique<PredicatedScalarEvolution>(*SE, *L)),
2195 PtrRtChecking(std::make_unique<RuntimePointerChecking>(SE)),
2196 DepChecker(std::make_unique<MemoryDepChecker>(*PSE, L)), TheLoop(L),
2197 NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1), CanVecMem(false),
2198 HasConvergentOp(false),
2199 HasDependenceInvolvingLoopInvariantAddress(false) {
2200 if (canAnalyzeLoop())
2201 analyzeLoop(AA, LI, TLI, DT);
2202}
2203
2204void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
2205 if (CanVecMem) {
2206 OS.indent(Depth) << "Memory dependences are safe";
2207 if (MaxSafeDepDistBytes != -1ULL)
2208 OS << " with a maximum dependence distance of " << MaxSafeDepDistBytes
2209 << " bytes";
2210 if (PtrRtChecking->Need)
2211 OS << " with run-time checks";
2212 OS << "\n";
2213 }
2214
2215 if (HasConvergentOp)
2216 OS.indent(Depth) << "Has convergent operation in loop\n";
2217
2218 if (Report)
2219 OS.indent(Depth) << "Report: " << Report->getMsg() << "\n";
2220
2221 if (auto *Dependences = DepChecker->getDependences()) {
2222 OS.indent(Depth) << "Dependences:\n";
2223 for (auto &Dep : *Dependences) {
2224 Dep.print(OS, Depth + 2, DepChecker->getMemoryInstructions());
2225 OS << "\n";
2226 }
2227 } else
2228 OS.indent(Depth) << "Too many dependences, not recorded\n";
2229
2230 // List the pair of accesses need run-time checks to prove independence.
2231 PtrRtChecking->print(OS, Depth);
2232 OS << "\n";
2233
2234 OS.indent(Depth) << "Non vectorizable stores to invariant address were "
2235 << (HasDependenceInvolvingLoopInvariantAddress ? "" : "not ")
2236 << "found in loop.\n";
2237
2238 OS.indent(Depth) << "SCEV assumptions:\n";
2239 PSE->getUnionPredicate().print(OS, Depth);
2240
2241 OS << "\n";
2242
2243 OS.indent(Depth) << "Expressions re-written:\n";
2244 PSE->print(OS, Depth);
2245}
2246
2247LoopAccessLegacyAnalysis::LoopAccessLegacyAnalysis() : FunctionPass(ID) {
2248 initializeLoopAccessLegacyAnalysisPass(*PassRegistry::getPassRegistry());
2249}
2250
2251const LoopAccessInfo &LoopAccessLegacyAnalysis::getInfo(Loop *L) {
2252 auto &LAI = LoopAccessInfoMap[L];
2253
2254 if (!LAI)
2255 LAI = std::make_unique<LoopAccessInfo>(L, SE, TLI, AA, DT, LI);
2256
2257 return *LAI.get();
2258}
2259
2260void LoopAccessLegacyAnalysis::print(raw_ostream &OS, const Module *M) const {
2261 LoopAccessLegacyAnalysis &LAA = *const_cast<LoopAccessLegacyAnalysis *>(this);
2262
2263 for (Loop *TopLevelLoop : *LI)
2264 for (Loop *L : depth_first(TopLevelLoop)) {
2265 OS.indent(2) << L->getHeader()->getName() << ":\n";
2266 auto &LAI = LAA.getInfo(L);
2267 LAI.print(OS, 4);
2268 }
2269}
2270
2271bool LoopAccessLegacyAnalysis::runOnFunction(Function &F) {
2272 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
2273 auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
2274 TLI = TLIP ? &TLIP->getTLI(F) : nullptr;
2275 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
2276 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
2277 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
2278
2279 return false;
2280}
2281
2282void LoopAccessLegacyAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
2283 AU.addRequiredTransitive<ScalarEvolutionWrapperPass>();
2284 AU.addRequiredTransitive<AAResultsWrapperPass>();
2285 AU.addRequiredTransitive<DominatorTreeWrapperPass>();
2286 AU.addRequiredTransitive<LoopInfoWrapperPass>();
2287
2288 AU.setPreservesAll();
2289}
2290
2291char LoopAccessLegacyAnalysis::ID = 0;
2292static const char laa_name[] = "Loop Access Analysis";
2293#define LAA_NAME"loop-accesses" "loop-accesses"
2294
2295INITIALIZE_PASS_BEGIN(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true)static void *initializeLoopAccessLegacyAnalysisPassOnce(PassRegistry
&Registry) {
2296INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry);
2297INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)initializeScalarEvolutionWrapperPassPass(Registry);
2298INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
2299INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry);
2300INITIALIZE_PASS_END(LoopAccessLegacyAnalysis, LAA_NAME, laa_name, false, true)PassInfo *PI = new PassInfo( laa_name, "loop-accesses", &
LoopAccessLegacyAnalysis::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LoopAccessLegacyAnalysis>), false, true); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeLoopAccessLegacyAnalysisPassFlag
; void llvm::initializeLoopAccessLegacyAnalysisPass(PassRegistry
&Registry) { llvm::call_once(InitializeLoopAccessLegacyAnalysisPassFlag
, initializeLoopAccessLegacyAnalysisPassOnce, std::ref(Registry
)); }
2301
2302AnalysisKey LoopAccessAnalysis::Key;
2303
2304LoopAccessInfo LoopAccessAnalysis::run(Loop &L, LoopAnalysisManager &AM,
2305 LoopStandardAnalysisResults &AR) {
2306 return LoopAccessInfo(&L, &AR.SE, &AR.TLI, &AR.AA, &AR.DT, &AR.LI);
2307}
2308
2309namespace llvm {
2310
2311 Pass *createLAAPass() {
2312 return new LoopAccessLegacyAnalysis();
2313 }
2314
2315} // end namespace llvm