Bug Summary

File:src/gnu/usr.bin/clang/libLLVM/../../../llvm/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
Warning:line 4326, column 24
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 SimplifyCFG.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 static -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" -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 -stack-protector 2 -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/Transforms/Utils/SimplifyCFG.cpp
1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
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// Peephole optimize the CFG.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/ADT/APInt.h"
14#include "llvm/ADT/ArrayRef.h"
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/MapVector.h"
17#include "llvm/ADT/Optional.h"
18#include "llvm/ADT/STLExtras.h"
19#include "llvm/ADT/ScopeExit.h"
20#include "llvm/ADT/Sequence.h"
21#include "llvm/ADT/SetOperations.h"
22#include "llvm/ADT/SetVector.h"
23#include "llvm/ADT/SmallPtrSet.h"
24#include "llvm/ADT/SmallVector.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/ADT/StringRef.h"
27#include "llvm/Analysis/AssumptionCache.h"
28#include "llvm/Analysis/ConstantFolding.h"
29#include "llvm/Analysis/EHPersonalities.h"
30#include "llvm/Analysis/GuardUtils.h"
31#include "llvm/Analysis/InstructionSimplify.h"
32#include "llvm/Analysis/MemorySSA.h"
33#include "llvm/Analysis/MemorySSAUpdater.h"
34#include "llvm/Analysis/TargetTransformInfo.h"
35#include "llvm/Analysis/ValueTracking.h"
36#include "llvm/IR/Attributes.h"
37#include "llvm/IR/BasicBlock.h"
38#include "llvm/IR/CFG.h"
39#include "llvm/IR/Constant.h"
40#include "llvm/IR/ConstantRange.h"
41#include "llvm/IR/Constants.h"
42#include "llvm/IR/DataLayout.h"
43#include "llvm/IR/DerivedTypes.h"
44#include "llvm/IR/Function.h"
45#include "llvm/IR/GlobalValue.h"
46#include "llvm/IR/GlobalVariable.h"
47#include "llvm/IR/IRBuilder.h"
48#include "llvm/IR/InstrTypes.h"
49#include "llvm/IR/Instruction.h"
50#include "llvm/IR/Instructions.h"
51#include "llvm/IR/IntrinsicInst.h"
52#include "llvm/IR/Intrinsics.h"
53#include "llvm/IR/LLVMContext.h"
54#include "llvm/IR/MDBuilder.h"
55#include "llvm/IR/Metadata.h"
56#include "llvm/IR/Module.h"
57#include "llvm/IR/NoFolder.h"
58#include "llvm/IR/Operator.h"
59#include "llvm/IR/PatternMatch.h"
60#include "llvm/IR/PseudoProbe.h"
61#include "llvm/IR/Type.h"
62#include "llvm/IR/Use.h"
63#include "llvm/IR/User.h"
64#include "llvm/IR/Value.h"
65#include "llvm/IR/ValueHandle.h"
66#include "llvm/Support/BranchProbability.h"
67#include "llvm/Support/Casting.h"
68#include "llvm/Support/CommandLine.h"
69#include "llvm/Support/Debug.h"
70#include "llvm/Support/ErrorHandling.h"
71#include "llvm/Support/KnownBits.h"
72#include "llvm/Support/MathExtras.h"
73#include "llvm/Support/raw_ostream.h"
74#include "llvm/Transforms/Utils/BasicBlockUtils.h"
75#include "llvm/Transforms/Utils/Local.h"
76#include "llvm/Transforms/Utils/SSAUpdater.h"
77#include "llvm/Transforms/Utils/ValueMapper.h"
78#include <algorithm>
79#include <cassert>
80#include <climits>
81#include <cstddef>
82#include <cstdint>
83#include <iterator>
84#include <map>
85#include <set>
86#include <tuple>
87#include <utility>
88#include <vector>
89
90using namespace llvm;
91using namespace PatternMatch;
92
93#define DEBUG_TYPE"simplifycfg" "simplifycfg"
94
95cl::opt<bool> llvm::RequireAndPreserveDomTree(
96 "simplifycfg-require-and-preserve-domtree", cl::Hidden, cl::ZeroOrMore,
97 cl::init(false),
98 cl::desc("Temorary development switch used to gradually uplift SimplifyCFG "
99 "into preserving DomTree,"));
100
101// Chosen as 2 so as to be cheap, but still to have enough power to fold
102// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
103// To catch this, we need to fold a compare and a select, hence '2' being the
104// minimum reasonable default.
105static cl::opt<unsigned> PHINodeFoldingThreshold(
106 "phi-node-folding-threshold", cl::Hidden, cl::init(2),
107 cl::desc(
108 "Control the amount of phi node folding to perform (default = 2)"));
109
110static cl::opt<unsigned> TwoEntryPHINodeFoldingThreshold(
111 "two-entry-phi-node-folding-threshold", cl::Hidden, cl::init(4),
112 cl::desc("Control the maximal total instruction cost that we are willing "
113 "to speculatively execute to fold a 2-entry PHI node into a "
114 "select (default = 4)"));
115
116static cl::opt<bool>
117 HoistCommon("simplifycfg-hoist-common", cl::Hidden, cl::init(true),
118 cl::desc("Hoist common instructions up to the parent block"));
119
120static cl::opt<bool>
121 SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
122 cl::desc("Sink common instructions down to the end block"));
123
124static cl::opt<bool> HoistCondStores(
125 "simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
126 cl::desc("Hoist conditional stores if an unconditional store precedes"));
127
128static cl::opt<bool> MergeCondStores(
129 "simplifycfg-merge-cond-stores", cl::Hidden, cl::init(true),
130 cl::desc("Hoist conditional stores even if an unconditional store does not "
131 "precede - hoist multiple conditional stores into a single "
132 "predicated store"));
133
134static cl::opt<bool> MergeCondStoresAggressively(
135 "simplifycfg-merge-cond-stores-aggressively", cl::Hidden, cl::init(false),
136 cl::desc("When merging conditional stores, do so even if the resultant "
137 "basic blocks are unlikely to be if-converted as a result"));
138
139static cl::opt<bool> SpeculateOneExpensiveInst(
140 "speculate-one-expensive-inst", cl::Hidden, cl::init(true),
141 cl::desc("Allow exactly one expensive instruction to be speculatively "
142 "executed"));
143
144static cl::opt<unsigned> MaxSpeculationDepth(
145 "max-speculation-depth", cl::Hidden, cl::init(10),
146 cl::desc("Limit maximum recursion depth when calculating costs of "
147 "speculatively executed instructions"));
148
149static cl::opt<int>
150 MaxSmallBlockSize("simplifycfg-max-small-block-size", cl::Hidden,
151 cl::init(10),
152 cl::desc("Max size of a block which is still considered "
153 "small enough to thread through"));
154
155// Two is chosen to allow one negation and a logical combine.
156static cl::opt<unsigned>
157 BranchFoldThreshold("simplifycfg-branch-fold-threshold", cl::Hidden,
158 cl::init(2),
159 cl::desc("Maximum cost of combining conditions when "
160 "folding branches"));
161
162STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps")static llvm::Statistic NumBitMaps = {"simplifycfg", "NumBitMaps"
, "Number of switch instructions turned into bitmaps"}
;
163STATISTIC(NumLinearMaps,static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping"}
164 "Number of switch instructions turned into linear mapping")static llvm::Statistic NumLinearMaps = {"simplifycfg", "NumLinearMaps"
, "Number of switch instructions turned into linear mapping"}
;
165STATISTIC(NumLookupTables,static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables"}
166 "Number of switch instructions turned into lookup tables")static llvm::Statistic NumLookupTables = {"simplifycfg", "NumLookupTables"
, "Number of switch instructions turned into lookup tables"}
;
167STATISTIC(static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
}
168 NumLookupTablesHoles,static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
}
169 "Number of switch instructions turned into lookup tables (holes checked)")static llvm::Statistic NumLookupTablesHoles = {"simplifycfg",
"NumLookupTablesHoles", "Number of switch instructions turned into lookup tables (holes checked)"
}
;
170STATISTIC(NumTableCmpReuses, "Number of reused switch table lookup compares")static llvm::Statistic NumTableCmpReuses = {"simplifycfg", "NumTableCmpReuses"
, "Number of reused switch table lookup compares"}
;
171STATISTIC(NumFoldValueComparisonIntoPredecessors,static llvm::Statistic NumFoldValueComparisonIntoPredecessors
= {"simplifycfg", "NumFoldValueComparisonIntoPredecessors", "Number of value comparisons folded into predecessor basic blocks"
}
172 "Number of value comparisons folded into predecessor basic blocks")static llvm::Statistic NumFoldValueComparisonIntoPredecessors
= {"simplifycfg", "NumFoldValueComparisonIntoPredecessors", "Number of value comparisons folded into predecessor basic blocks"
}
;
173STATISTIC(NumFoldBranchToCommonDest,static llvm::Statistic NumFoldBranchToCommonDest = {"simplifycfg"
, "NumFoldBranchToCommonDest", "Number of branches folded into predecessor basic block"
}
174 "Number of branches folded into predecessor basic block")static llvm::Statistic NumFoldBranchToCommonDest = {"simplifycfg"
, "NumFoldBranchToCommonDest", "Number of branches folded into predecessor basic block"
}
;
175STATISTIC(static llvm::Statistic NumHoistCommonCode = {"simplifycfg", "NumHoistCommonCode"
, "Number of common instruction 'blocks' hoisted up to the begin block"
}
176 NumHoistCommonCode,static llvm::Statistic NumHoistCommonCode = {"simplifycfg", "NumHoistCommonCode"
, "Number of common instruction 'blocks' hoisted up to the begin block"
}
177 "Number of common instruction 'blocks' hoisted up to the begin block")static llvm::Statistic NumHoistCommonCode = {"simplifycfg", "NumHoistCommonCode"
, "Number of common instruction 'blocks' hoisted up to the begin block"
}
;
178STATISTIC(NumHoistCommonInstrs,static llvm::Statistic NumHoistCommonInstrs = {"simplifycfg",
"NumHoistCommonInstrs", "Number of common instructions hoisted up to the begin block"
}
179 "Number of common instructions hoisted up to the begin block")static llvm::Statistic NumHoistCommonInstrs = {"simplifycfg",
"NumHoistCommonInstrs", "Number of common instructions hoisted up to the begin block"
}
;
180STATISTIC(NumSinkCommonCode,static llvm::Statistic NumSinkCommonCode = {"simplifycfg", "NumSinkCommonCode"
, "Number of common instruction 'blocks' sunk down to the end block"
}
181 "Number of common instruction 'blocks' sunk down to the end block")static llvm::Statistic NumSinkCommonCode = {"simplifycfg", "NumSinkCommonCode"
, "Number of common instruction 'blocks' sunk down to the end block"
}
;
182STATISTIC(NumSinkCommonInstrs,static llvm::Statistic NumSinkCommonInstrs = {"simplifycfg", "NumSinkCommonInstrs"
, "Number of common instructions sunk down to the end block"}
183 "Number of common instructions sunk down to the end block")static llvm::Statistic NumSinkCommonInstrs = {"simplifycfg", "NumSinkCommonInstrs"
, "Number of common instructions sunk down to the end block"}
;
184STATISTIC(NumSpeculations, "Number of speculative executed instructions")static llvm::Statistic NumSpeculations = {"simplifycfg", "NumSpeculations"
, "Number of speculative executed instructions"}
;
185STATISTIC(NumInvokes,static llvm::Statistic NumInvokes = {"simplifycfg", "NumInvokes"
, "Number of invokes with empty resume blocks simplified into calls"
}
186 "Number of invokes with empty resume blocks simplified into calls")static llvm::Statistic NumInvokes = {"simplifycfg", "NumInvokes"
, "Number of invokes with empty resume blocks simplified into calls"
}
;
187
188namespace {
189
190// The first field contains the value that the switch produces when a certain
191// case group is selected, and the second field is a vector containing the
192// cases composing the case group.
193using SwitchCaseResultVectorTy =
194 SmallVector<std::pair<Constant *, SmallVector<ConstantInt *, 4>>, 2>;
195
196// The first field contains the phi node that generates a result of the switch
197// and the second field contains the value generated for a certain case in the
198// switch for that PHI.
199using SwitchCaseResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
200
201/// ValueEqualityComparisonCase - Represents a case of a switch.
202struct ValueEqualityComparisonCase {
203 ConstantInt *Value;
204 BasicBlock *Dest;
205
206 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest)
207 : Value(Value), Dest(Dest) {}
208
209 bool operator<(ValueEqualityComparisonCase RHS) const {
210 // Comparing pointers is ok as we only rely on the order for uniquing.
211 return Value < RHS.Value;
212 }
213
214 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; }
215};
216
217class SimplifyCFGOpt {
218 const TargetTransformInfo &TTI;
219 DomTreeUpdater *DTU;
220 const DataLayout &DL;
221 ArrayRef<WeakVH> LoopHeaders;
222 const SimplifyCFGOptions &Options;
223 bool Resimplify;
224
225 Value *isValueEqualityComparison(Instruction *TI);
226 BasicBlock *GetValueEqualityComparisonCases(
227 Instruction *TI, std::vector<ValueEqualityComparisonCase> &Cases);
228 bool SimplifyEqualityComparisonWithOnlyPredecessor(Instruction *TI,
229 BasicBlock *Pred,
230 IRBuilder<> &Builder);
231 bool PerformValueComparisonIntoPredecessorFolding(Instruction *TI, Value *&CV,
232 Instruction *PTI,
233 IRBuilder<> &Builder);
234 bool FoldValueComparisonIntoPredecessors(Instruction *TI,
235 IRBuilder<> &Builder);
236
237 bool simplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
238 bool simplifySingleResume(ResumeInst *RI);
239 bool simplifyCommonResume(ResumeInst *RI);
240 bool simplifyCleanupReturn(CleanupReturnInst *RI);
241 bool simplifyUnreachable(UnreachableInst *UI);
242 bool simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
243 bool simplifyIndirectBr(IndirectBrInst *IBI);
244 bool simplifyBranch(BranchInst *Branch, IRBuilder<> &Builder);
245 bool simplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder);
246 bool simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder);
247
248 bool tryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
249 IRBuilder<> &Builder);
250
251 bool HoistThenElseCodeToIf(BranchInst *BI, const TargetTransformInfo &TTI,
252 bool EqTermsOnly);
253 bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
254 const TargetTransformInfo &TTI);
255 bool SimplifyTerminatorOnSelect(Instruction *OldTerm, Value *Cond,
256 BasicBlock *TrueBB, BasicBlock *FalseBB,
257 uint32_t TrueWeight, uint32_t FalseWeight);
258 bool SimplifyBranchOnICmpChain(BranchInst *BI, IRBuilder<> &Builder,
259 const DataLayout &DL);
260 bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select);
261 bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI);
262 bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder);
263
264public:
265 SimplifyCFGOpt(const TargetTransformInfo &TTI, DomTreeUpdater *DTU,
266 const DataLayout &DL, ArrayRef<WeakVH> LoopHeaders,
267 const SimplifyCFGOptions &Opts)
268 : TTI(TTI), DTU(DTU), DL(DL), LoopHeaders(LoopHeaders), Options(Opts) {
269 assert((!DTU || !DTU->hasPostDomTree()) &&((void)0)
270 "SimplifyCFG is not yet capable of maintaining validity of a "((void)0)
271 "PostDomTree, so don't ask for it.")((void)0);
272 }
273
274 bool simplifyOnce(BasicBlock *BB);
275 bool simplifyOnceImpl(BasicBlock *BB);
276 bool run(BasicBlock *BB);
277
278 // Helper to set Resimplify and return change indication.
279 bool requestResimplify() {
280 Resimplify = true;
281 return true;
282 }
283};
284
285} // end anonymous namespace
286
287/// Return true if it is safe to merge these two
288/// terminator instructions together.
289static bool
290SafeToMergeTerminators(Instruction *SI1, Instruction *SI2,
291 SmallSetVector<BasicBlock *, 4> *FailBlocks = nullptr) {
292 if (SI1 == SI2)
293 return false; // Can't merge with self!
294
295 // It is not safe to merge these two switch instructions if they have a common
296 // successor, and if that successor has a PHI node, and if *that* PHI node has
297 // conflicting incoming values from the two switch blocks.
298 BasicBlock *SI1BB = SI1->getParent();
299 BasicBlock *SI2BB = SI2->getParent();
300
301 SmallPtrSet<BasicBlock *, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
302 bool Fail = false;
303 for (BasicBlock *Succ : successors(SI2BB))
304 if (SI1Succs.count(Succ))
305 for (BasicBlock::iterator BBI = Succ->begin(); isa<PHINode>(BBI); ++BBI) {
306 PHINode *PN = cast<PHINode>(BBI);
307 if (PN->getIncomingValueForBlock(SI1BB) !=
308 PN->getIncomingValueForBlock(SI2BB)) {
309 if (FailBlocks)
310 FailBlocks->insert(Succ);
311 Fail = true;
312 }
313 }
314
315 return !Fail;
316}
317
318/// Update PHI nodes in Succ to indicate that there will now be entries in it
319/// from the 'NewPred' block. The values that will be flowing into the PHI nodes
320/// will be the same as those coming in from ExistPred, an existing predecessor
321/// of Succ.
322static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
323 BasicBlock *ExistPred,
324 MemorySSAUpdater *MSSAU = nullptr) {
325 for (PHINode &PN : Succ->phis())
326 PN.addIncoming(PN.getIncomingValueForBlock(ExistPred), NewPred);
327 if (MSSAU)
328 if (auto *MPhi = MSSAU->getMemorySSA()->getMemoryAccess(Succ))
329 MPhi->addIncoming(MPhi->getIncomingValueForBlock(ExistPred), NewPred);
330}
331
332/// Compute an abstract "cost" of speculating the given instruction,
333/// which is assumed to be safe to speculate. TCC_Free means cheap,
334/// TCC_Basic means less cheap, and TCC_Expensive means prohibitively
335/// expensive.
336static InstructionCost computeSpeculationCost(const User *I,
337 const TargetTransformInfo &TTI) {
338 assert(isSafeToSpeculativelyExecute(I) &&((void)0)
339 "Instruction is not safe to speculatively execute!")((void)0);
340 return TTI.getUserCost(I, TargetTransformInfo::TCK_SizeAndLatency);
341}
342
343/// If we have a merge point of an "if condition" as accepted above,
344/// return true if the specified value dominates the block. We
345/// don't handle the true generality of domination here, just a special case
346/// which works well enough for us.
347///
348/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
349/// see if V (which must be an instruction) and its recursive operands
350/// that do not dominate BB have a combined cost lower than Budget and
351/// are non-trapping. If both are true, the instruction is inserted into the
352/// set and true is returned.
353///
354/// The cost for most non-trapping instructions is defined as 1 except for
355/// Select whose cost is 2.
356///
357/// After this function returns, Cost is increased by the cost of
358/// V plus its non-dominating operands. If that cost is greater than
359/// Budget, false is returned and Cost is undefined.
360static bool dominatesMergePoint(Value *V, BasicBlock *BB,
361 SmallPtrSetImpl<Instruction *> &AggressiveInsts,
362 InstructionCost &Cost,
363 InstructionCost Budget,
364 const TargetTransformInfo &TTI,
365 unsigned Depth = 0) {
366 // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
367 // so limit the recursion depth.
368 // TODO: While this recursion limit does prevent pathological behavior, it
369 // would be better to track visited instructions to avoid cycles.
370 if (Depth == MaxSpeculationDepth)
371 return false;
372
373 Instruction *I = dyn_cast<Instruction>(V);
374 if (!I) {
375 // Non-instructions all dominate instructions, but not all constantexprs
376 // can be executed unconditionally.
377 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
378 if (C->canTrap())
379 return false;
380 return true;
381 }
382 BasicBlock *PBB = I->getParent();
383
384 // We don't want to allow weird loops that might have the "if condition" in
385 // the bottom of this block.
386 if (PBB == BB)
387 return false;
388
389 // If this instruction is defined in a block that contains an unconditional
390 // branch to BB, then it must be in the 'conditional' part of the "if
391 // statement". If not, it definitely dominates the region.
392 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
393 if (!BI || BI->isConditional() || BI->getSuccessor(0) != BB)
394 return true;
395
396 // If we have seen this instruction before, don't count it again.
397 if (AggressiveInsts.count(I))
398 return true;
399
400 // Okay, it looks like the instruction IS in the "condition". Check to
401 // see if it's a cheap instruction to unconditionally compute, and if it
402 // only uses stuff defined outside of the condition. If so, hoist it out.
403 if (!isSafeToSpeculativelyExecute(I))
404 return false;
405
406 Cost += computeSpeculationCost(I, TTI);
407
408 // Allow exactly one instruction to be speculated regardless of its cost
409 // (as long as it is safe to do so).
410 // This is intended to flatten the CFG even if the instruction is a division
411 // or other expensive operation. The speculation of an expensive instruction
412 // is expected to be undone in CodeGenPrepare if the speculation has not
413 // enabled further IR optimizations.
414 if (Cost > Budget &&
415 (!SpeculateOneExpensiveInst || !AggressiveInsts.empty() || Depth > 0 ||
416 !Cost.isValid()))
417 return false;
418
419 // Okay, we can only really hoist these out if their operands do
420 // not take us over the cost threshold.
421 for (Use &Op : I->operands())
422 if (!dominatesMergePoint(Op, BB, AggressiveInsts, Cost, Budget, TTI,
423 Depth + 1))
424 return false;
425 // Okay, it's safe to do this! Remember this instruction.
426 AggressiveInsts.insert(I);
427 return true;
428}
429
430/// Extract ConstantInt from value, looking through IntToPtr
431/// and PointerNullValue. Return NULL if value is not a constant int.
432static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
433 // Normal constant int.
434 ConstantInt *CI = dyn_cast<ConstantInt>(V);
435 if (CI || !isa<Constant>(V) || !V->getType()->isPointerTy())
436 return CI;
437
438 // This is some kind of pointer constant. Turn it into a pointer-sized
439 // ConstantInt if possible.
440 IntegerType *PtrTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
441
442 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
443 if (isa<ConstantPointerNull>(V))
444 return ConstantInt::get(PtrTy, 0);
445
446 // IntToPtr const int.
447 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
448 if (CE->getOpcode() == Instruction::IntToPtr)
449 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
450 // The constant is very likely to have the right type already.
451 if (CI->getType() == PtrTy)
452 return CI;
453 else
454 return cast<ConstantInt>(
455 ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
456 }
457 return nullptr;
458}
459
460namespace {
461
462/// Given a chain of or (||) or and (&&) comparison of a value against a
463/// constant, this will try to recover the information required for a switch
464/// structure.
465/// It will depth-first traverse the chain of comparison, seeking for patterns
466/// like %a == 12 or %a < 4 and combine them to produce a set of integer
467/// representing the different cases for the switch.
468/// Note that if the chain is composed of '||' it will build the set of elements
469/// that matches the comparisons (i.e. any of this value validate the chain)
470/// while for a chain of '&&' it will build the set elements that make the test
471/// fail.
472struct ConstantComparesGatherer {
473 const DataLayout &DL;
474
475 /// Value found for the switch comparison
476 Value *CompValue = nullptr;
477
478 /// Extra clause to be checked before the switch
479 Value *Extra = nullptr;
480
481 /// Set of integers to match in switch
482 SmallVector<ConstantInt *, 8> Vals;
483
484 /// Number of comparisons matched in the and/or chain
485 unsigned UsedICmps = 0;
486
487 /// Construct and compute the result for the comparison instruction Cond
488 ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL) : DL(DL) {
489 gather(Cond);
490 }
491
492 ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
493 ConstantComparesGatherer &
494 operator=(const ConstantComparesGatherer &) = delete;
495
496private:
497 /// Try to set the current value used for the comparison, it succeeds only if
498 /// it wasn't set before or if the new value is the same as the old one
499 bool setValueOnce(Value *NewVal) {
500 if (CompValue && CompValue != NewVal)
501 return false;
502 CompValue = NewVal;
503 return (CompValue != nullptr);
504 }
505
506 /// Try to match Instruction "I" as a comparison against a constant and
507 /// populates the array Vals with the set of values that match (or do not
508 /// match depending on isEQ).
509 /// Return false on failure. On success, the Value the comparison matched
510 /// against is placed in CompValue.
511 /// If CompValue is already set, the function is expected to fail if a match
512 /// is found but the value compared to is different.
513 bool matchInstruction(Instruction *I, bool isEQ) {
514 // If this is an icmp against a constant, handle this as one of the cases.
515 ICmpInst *ICI;
516 ConstantInt *C;
517 if (!((ICI = dyn_cast<ICmpInst>(I)) &&
518 (C = GetConstantInt(I->getOperand(1), DL)))) {
519 return false;
520 }
521
522 Value *RHSVal;
523 const APInt *RHSC;
524
525 // Pattern match a special case
526 // (x & ~2^z) == y --> x == y || x == y|2^z
527 // This undoes a transformation done by instcombine to fuse 2 compares.
528 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) {
529 // It's a little bit hard to see why the following transformations are
530 // correct. Here is a CVC3 program to verify them for 64-bit values:
531
532 /*
533 ONE : BITVECTOR(64) = BVZEROEXTEND(0bin1, 63);
534 x : BITVECTOR(64);
535 y : BITVECTOR(64);
536 z : BITVECTOR(64);
537 mask : BITVECTOR(64) = BVSHL(ONE, z);
538 QUERY( (y & ~mask = y) =>
539 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
540 );
541 QUERY( (y | mask = y) =>
542 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
543 );
544 */
545
546 // Please note that each pattern must be a dual implication (<--> or
547 // iff). One directional implication can create spurious matches. If the
548 // implication is only one-way, an unsatisfiable condition on the left
549 // side can imply a satisfiable condition on the right side. Dual
550 // implication ensures that satisfiable conditions are transformed to
551 // other satisfiable conditions and unsatisfiable conditions are
552 // transformed to other unsatisfiable conditions.
553
554 // Here is a concrete example of a unsatisfiable condition on the left
555 // implying a satisfiable condition on the right:
556 //
557 // mask = (1 << z)
558 // (x & ~mask) == y --> (x == y || x == (y | mask))
559 //
560 // Substituting y = 3, z = 0 yields:
561 // (x & -2) == 3 --> (x == 3 || x == 2)
562
563 // Pattern match a special case:
564 /*
565 QUERY( (y & ~mask = y) =>
566 ((x & ~mask = y) <=> (x = y OR x = (y | mask)))
567 );
568 */
569 if (match(ICI->getOperand(0),
570 m_And(m_Value(RHSVal), m_APInt(RHSC)))) {
571 APInt Mask = ~*RHSC;
572 if (Mask.isPowerOf2() && (C->getValue() & ~Mask) == C->getValue()) {
573 // If we already have a value for the switch, it has to match!
574 if (!setValueOnce(RHSVal))
575 return false;
576
577 Vals.push_back(C);
578 Vals.push_back(
579 ConstantInt::get(C->getContext(),
580 C->getValue() | Mask));
581 UsedICmps++;
582 return true;
583 }
584 }
585
586 // Pattern match a special case:
587 /*
588 QUERY( (y | mask = y) =>
589 ((x | mask = y) <=> (x = y OR x = (y & ~mask)))
590 );
591 */
592 if (match(ICI->getOperand(0),
593 m_Or(m_Value(RHSVal), m_APInt(RHSC)))) {
594 APInt Mask = *RHSC;
595 if (Mask.isPowerOf2() && (C->getValue() | Mask) == C->getValue()) {
596 // If we already have a value for the switch, it has to match!
597 if (!setValueOnce(RHSVal))
598 return false;
599
600 Vals.push_back(C);
601 Vals.push_back(ConstantInt::get(C->getContext(),
602 C->getValue() & ~Mask));
603 UsedICmps++;
604 return true;
605 }
606 }
607
608 // If we already have a value for the switch, it has to match!
609 if (!setValueOnce(ICI->getOperand(0)))
610 return false;
611
612 UsedICmps++;
613 Vals.push_back(C);
614 return ICI->getOperand(0);
615 }
616
617 // If we have "x ult 3", for example, then we can add 0,1,2 to the set.
618 ConstantRange Span =
619 ConstantRange::makeExactICmpRegion(ICI->getPredicate(), C->getValue());
620
621 // Shift the range if the compare is fed by an add. This is the range
622 // compare idiom as emitted by instcombine.
623 Value *CandidateVal = I->getOperand(0);
624 if (match(I->getOperand(0), m_Add(m_Value(RHSVal), m_APInt(RHSC)))) {
625 Span = Span.subtract(*RHSC);
626 CandidateVal = RHSVal;
627 }
628
629 // If this is an and/!= check, then we are looking to build the set of
630 // value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
631 // x != 0 && x != 1.
632 if (!isEQ)
633 Span = Span.inverse();
634
635 // If there are a ton of values, we don't want to make a ginormous switch.
636 if (Span.isSizeLargerThan(8) || Span.isEmptySet()) {
637 return false;
638 }
639
640 // If we already have a value for the switch, it has to match!
641 if (!setValueOnce(CandidateVal))
642 return false;
643
644 // Add all values from the range to the set
645 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
646 Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
647
648 UsedICmps++;
649 return true;
650 }
651
652 /// Given a potentially 'or'd or 'and'd together collection of icmp
653 /// eq/ne/lt/gt instructions that compare a value against a constant, extract
654 /// the value being compared, and stick the list constants into the Vals
655 /// vector.
656 /// One "Extra" case is allowed to differ from the other.
657 void gather(Value *V) {
658 bool isEQ = match(V, m_LogicalOr(m_Value(), m_Value()));
659
660 // Keep a stack (SmallVector for efficiency) for depth-first traversal
661 SmallVector<Value *, 8> DFT;
662 SmallPtrSet<Value *, 8> Visited;
663
664 // Initialize
665 Visited.insert(V);
666 DFT.push_back(V);
667
668 while (!DFT.empty()) {
669 V = DFT.pop_back_val();
670
671 if (Instruction *I = dyn_cast<Instruction>(V)) {
672 // If it is a || (or && depending on isEQ), process the operands.
673 Value *Op0, *Op1;
674 if (isEQ ? match(I, m_LogicalOr(m_Value(Op0), m_Value(Op1)))
675 : match(I, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
676 if (Visited.insert(Op1).second)
677 DFT.push_back(Op1);
678 if (Visited.insert(Op0).second)
679 DFT.push_back(Op0);
680
681 continue;
682 }
683
684 // Try to match the current instruction
685 if (matchInstruction(I, isEQ))
686 // Match succeed, continue the loop
687 continue;
688 }
689
690 // One element of the sequence of || (or &&) could not be match as a
691 // comparison against the same value as the others.
692 // We allow only one "Extra" case to be checked before the switch
693 if (!Extra) {
694 Extra = V;
695 continue;
696 }
697 // Failed to parse a proper sequence, abort now
698 CompValue = nullptr;
699 break;
700 }
701 }
702};
703
704} // end anonymous namespace
705
706static void EraseTerminatorAndDCECond(Instruction *TI,
707 MemorySSAUpdater *MSSAU = nullptr) {
708 Instruction *Cond = nullptr;
709 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
710 Cond = dyn_cast<Instruction>(SI->getCondition());
711 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
712 if (BI->isConditional())
713 Cond = dyn_cast<Instruction>(BI->getCondition());
714 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
715 Cond = dyn_cast<Instruction>(IBI->getAddress());
716 }
717
718 TI->eraseFromParent();
719 if (Cond)
720 RecursivelyDeleteTriviallyDeadInstructions(Cond, nullptr, MSSAU);
721}
722
723/// Return true if the specified terminator checks
724/// to see if a value is equal to constant integer value.
725Value *SimplifyCFGOpt::isValueEqualityComparison(Instruction *TI) {
726 Value *CV = nullptr;
727 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
728 // Do not permit merging of large switch instructions into their
729 // predecessors unless there is only one predecessor.
730 if (!SI->getParent()->hasNPredecessorsOrMore(128 / SI->getNumSuccessors()))
731 CV = SI->getCondition();
732 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
733 if (BI->isConditional() && BI->getCondition()->hasOneUse())
734 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
735 if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), DL))
736 CV = ICI->getOperand(0);
737 }
738
739 // Unwrap any lossless ptrtoint cast.
740 if (CV) {
741 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) {
742 Value *Ptr = PTII->getPointerOperand();
743 if (PTII->getType() == DL.getIntPtrType(Ptr->getType()))
744 CV = Ptr;
745 }
746 }
747 return CV;
748}
749
750/// Given a value comparison instruction,
751/// decode all of the 'cases' that it represents and return the 'default' block.
752BasicBlock *SimplifyCFGOpt::GetValueEqualityComparisonCases(
753 Instruction *TI, std::vector<ValueEqualityComparisonCase> &Cases) {
754 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
755 Cases.reserve(SI->getNumCases());
756 for (auto Case : SI->cases())
757 Cases.push_back(ValueEqualityComparisonCase(Case.getCaseValue(),
758 Case.getCaseSuccessor()));
759 return SI->getDefaultDest();
760 }
761
762 BranchInst *BI = cast<BranchInst>(TI);
763 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
764 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
765 Cases.push_back(ValueEqualityComparisonCase(
766 GetConstantInt(ICI->getOperand(1), DL), Succ));
767 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
768}
769
770/// Given a vector of bb/value pairs, remove any entries
771/// in the list that match the specified block.
772static void
773EliminateBlockCases(BasicBlock *BB,
774 std::vector<ValueEqualityComparisonCase> &Cases) {
775 llvm::erase_value(Cases, BB);
776}
777
778/// Return true if there are any keys in C1 that exist in C2 as well.
779static bool ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1,
780 std::vector<ValueEqualityComparisonCase> &C2) {
781 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2;
782
783 // Make V1 be smaller than V2.
784 if (V1->size() > V2->size())
785 std::swap(V1, V2);
786
787 if (V1->empty())
788 return false;
789 if (V1->size() == 1) {
790 // Just scan V2.
791 ConstantInt *TheVal = (*V1)[0].Value;
792 for (unsigned i = 0, e = V2->size(); i != e; ++i)
793 if (TheVal == (*V2)[i].Value)
794 return true;
795 }
796
797 // Otherwise, just sort both lists and compare element by element.
798 array_pod_sort(V1->begin(), V1->end());
799 array_pod_sort(V2->begin(), V2->end());
800 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
801 while (i1 != e1 && i2 != e2) {
802 if ((*V1)[i1].Value == (*V2)[i2].Value)
803 return true;
804 if ((*V1)[i1].Value < (*V2)[i2].Value)
805 ++i1;
806 else
807 ++i2;
808 }
809 return false;
810}
811
812// Set branch weights on SwitchInst. This sets the metadata if there is at
813// least one non-zero weight.
814static void setBranchWeights(SwitchInst *SI, ArrayRef<uint32_t> Weights) {
815 // Check that there is at least one non-zero weight. Otherwise, pass
816 // nullptr to setMetadata which will erase the existing metadata.
817 MDNode *N = nullptr;
818 if (llvm::any_of(Weights, [](uint32_t W) { return W != 0; }))
819 N = MDBuilder(SI->getParent()->getContext()).createBranchWeights(Weights);
820 SI->setMetadata(LLVMContext::MD_prof, N);
821}
822
823// Similar to the above, but for branch and select instructions that take
824// exactly 2 weights.
825static void setBranchWeights(Instruction *I, uint32_t TrueWeight,
826 uint32_t FalseWeight) {
827 assert(isa<BranchInst>(I) || isa<SelectInst>(I))((void)0);
828 // Check that there is at least one non-zero weight. Otherwise, pass
829 // nullptr to setMetadata which will erase the existing metadata.
830 MDNode *N = nullptr;
831 if (TrueWeight || FalseWeight)
832 N = MDBuilder(I->getParent()->getContext())
833 .createBranchWeights(TrueWeight, FalseWeight);
834 I->setMetadata(LLVMContext::MD_prof, N);
835}
836
837/// If TI is known to be a terminator instruction and its block is known to
838/// only have a single predecessor block, check to see if that predecessor is
839/// also a value comparison with the same value, and if that comparison
840/// determines the outcome of this comparison. If so, simplify TI. This does a
841/// very limited form of jump threading.
842bool SimplifyCFGOpt::SimplifyEqualityComparisonWithOnlyPredecessor(
843 Instruction *TI, BasicBlock *Pred, IRBuilder<> &Builder) {
844 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
845 if (!PredVal)
846 return false; // Not a value comparison in predecessor.
847
848 Value *ThisVal = isValueEqualityComparison(TI);
849 assert(ThisVal && "This isn't a value comparison!!")((void)0);
850 if (ThisVal != PredVal)
851 return false; // Different predicates.
852
853 // TODO: Preserve branch weight metadata, similarly to how
854 // FoldValueComparisonIntoPredecessors preserves it.
855
856 // Find out information about when control will move from Pred to TI's block.
857 std::vector<ValueEqualityComparisonCase> PredCases;
858 BasicBlock *PredDef =
859 GetValueEqualityComparisonCases(Pred->getTerminator(), PredCases);
860 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
861
862 // Find information about how control leaves this block.
863 std::vector<ValueEqualityComparisonCase> ThisCases;
864 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
865 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
866
867 // If TI's block is the default block from Pred's comparison, potentially
868 // simplify TI based on this knowledge.
869 if (PredDef == TI->getParent()) {
870 // If we are here, we know that the value is none of those cases listed in
871 // PredCases. If there are any cases in ThisCases that are in PredCases, we
872 // can simplify TI.
873 if (!ValuesOverlap(PredCases, ThisCases))
874 return false;
875
876 if (isa<BranchInst>(TI)) {
877 // Okay, one of the successors of this condbr is dead. Convert it to a
878 // uncond br.
879 assert(ThisCases.size() == 1 && "Branch can only have one case!")((void)0);
880 // Insert the new branch.
881 Instruction *NI = Builder.CreateBr(ThisDef);
882 (void)NI;
883
884 // Remove PHI node entries for the dead edge.
885 ThisCases[0].Dest->removePredecessor(PredDef);
886
887 LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()do { } while (false)
888 << "Through successor TI: " << *TI << "Leaving: " << *NIdo { } while (false)
889 << "\n")do { } while (false);
890
891 EraseTerminatorAndDCECond(TI);
892
893 if (DTU)
894 DTU->applyUpdates(
895 {{DominatorTree::Delete, PredDef, ThisCases[0].Dest}});
896
897 return true;
898 }
899
900 SwitchInstProfUpdateWrapper SI = *cast<SwitchInst>(TI);
901 // Okay, TI has cases that are statically dead, prune them away.
902 SmallPtrSet<Constant *, 16> DeadCases;
903 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
904 DeadCases.insert(PredCases[i].Value);
905
906 LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()do { } while (false)
907 << "Through successor TI: " << *TI)do { } while (false);
908
909 SmallDenseMap<BasicBlock *, int, 8> NumPerSuccessorCases;
910 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
911 --i;
912 auto *Successor = i->getCaseSuccessor();
913 if (DTU)
914 ++NumPerSuccessorCases[Successor];
915 if (DeadCases.count(i->getCaseValue())) {
916 Successor->removePredecessor(PredDef);
917 SI.removeCase(i);
918 if (DTU)
919 --NumPerSuccessorCases[Successor];
920 }
921 }
922
923 if (DTU) {
924 std::vector<DominatorTree::UpdateType> Updates;
925 for (const std::pair<BasicBlock *, int> &I : NumPerSuccessorCases)
926 if (I.second == 0)
927 Updates.push_back({DominatorTree::Delete, PredDef, I.first});
928 DTU->applyUpdates(Updates);
929 }
930
931 LLVM_DEBUG(dbgs() << "Leaving: " << *TI << "\n")do { } while (false);
932 return true;
933 }
934
935 // Otherwise, TI's block must correspond to some matched value. Find out
936 // which value (or set of values) this is.
937 ConstantInt *TIV = nullptr;
938 BasicBlock *TIBB = TI->getParent();
939 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
940 if (PredCases[i].Dest == TIBB) {
941 if (TIV)
942 return false; // Cannot handle multiple values coming to this block.
943 TIV = PredCases[i].Value;
944 }
945 assert(TIV && "No edge from pred to succ?")((void)0);
946
947 // Okay, we found the one constant that our value can be if we get into TI's
948 // BB. Find out which successor will unconditionally be branched to.
949 BasicBlock *TheRealDest = nullptr;
950 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
951 if (ThisCases[i].Value == TIV) {
952 TheRealDest = ThisCases[i].Dest;
953 break;
954 }
955
956 // If not handled by any explicit cases, it is handled by the default case.
957 if (!TheRealDest)
958 TheRealDest = ThisDef;
959
960 SmallPtrSet<BasicBlock *, 2> RemovedSuccs;
961
962 // Remove PHI node entries for dead edges.
963 BasicBlock *CheckEdge = TheRealDest;
964 for (BasicBlock *Succ : successors(TIBB))
965 if (Succ != CheckEdge) {
966 if (Succ != TheRealDest)
967 RemovedSuccs.insert(Succ);
968 Succ->removePredecessor(TIBB);
969 } else
970 CheckEdge = nullptr;
971
972 // Insert the new branch.
973 Instruction *NI = Builder.CreateBr(TheRealDest);
974 (void)NI;
975
976 LLVM_DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()do { } while (false)
977 << "Through successor TI: " << *TI << "Leaving: " << *NIdo { } while (false)
978 << "\n")do { } while (false);
979
980 EraseTerminatorAndDCECond(TI);
981 if (DTU) {
982 SmallVector<DominatorTree::UpdateType, 2> Updates;
983 Updates.reserve(RemovedSuccs.size());
984 for (auto *RemovedSucc : RemovedSuccs)
985 Updates.push_back({DominatorTree::Delete, TIBB, RemovedSucc});
986 DTU->applyUpdates(Updates);
987 }
988 return true;
989}
990
991namespace {
992
993/// This class implements a stable ordering of constant
994/// integers that does not depend on their address. This is important for
995/// applications that sort ConstantInt's to ensure uniqueness.
996struct ConstantIntOrdering {
997 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
998 return LHS->getValue().ult(RHS->getValue());
999 }
1000};
1001
1002} // end anonymous namespace
1003
1004static int ConstantIntSortPredicate(ConstantInt *const *P1,
1005 ConstantInt *const *P2) {
1006 const ConstantInt *LHS = *P1;
1007 const ConstantInt *RHS = *P2;
1008 if (LHS == RHS)
1009 return 0;
1010 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1;
1011}
1012
1013static inline bool HasBranchWeights(const Instruction *I) {
1014 MDNode *ProfMD = I->getMetadata(LLVMContext::MD_prof);
1015 if (ProfMD && ProfMD->getOperand(0))
1016 if (MDString *MDS = dyn_cast<MDString>(ProfMD->getOperand(0)))
1017 return MDS->getString().equals("branch_weights");
1018
1019 return false;
1020}
1021
1022/// Get Weights of a given terminator, the default weight is at the front
1023/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
1024/// metadata.
1025static void GetBranchWeights(Instruction *TI,
1026 SmallVectorImpl<uint64_t> &Weights) {
1027 MDNode *MD = TI->getMetadata(LLVMContext::MD_prof);
1028 assert(MD)((void)0);
1029 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
1030 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(i));
1031 Weights.push_back(CI->getValue().getZExtValue());
1032 }
1033
1034 // If TI is a conditional eq, the default case is the false case,
1035 // and the corresponding branch-weight data is at index 2. We swap the
1036 // default weight to be the first entry.
1037 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1038 assert(Weights.size() == 2)((void)0);
1039 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
1040 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1041 std::swap(Weights.front(), Weights.back());
1042 }
1043}
1044
1045/// Keep halving the weights until all can fit in uint32_t.
1046static void FitWeights(MutableArrayRef<uint64_t> Weights) {
1047 uint64_t Max = *std::max_element(Weights.begin(), Weights.end());
1048 if (Max > UINT_MAX(2147483647 *2U +1U)) {
1049 unsigned Offset = 32 - countLeadingZeros(Max);
1050 for (uint64_t &I : Weights)
1051 I >>= Offset;
1052 }
1053}
1054
1055static void CloneInstructionsIntoPredecessorBlockAndUpdateSSAUses(
1056 BasicBlock *BB, BasicBlock *PredBlock, ValueToValueMapTy &VMap) {
1057 Instruction *PTI = PredBlock->getTerminator();
1058
1059 // If we have bonus instructions, clone them into the predecessor block.
1060 // Note that there may be multiple predecessor blocks, so we cannot move
1061 // bonus instructions to a predecessor block.
1062 for (Instruction &BonusInst : *BB) {
1063 if (isa<DbgInfoIntrinsic>(BonusInst) || BonusInst.isTerminator())
1064 continue;
1065
1066 Instruction *NewBonusInst = BonusInst.clone();
1067
1068 if (PTI->getDebugLoc() != NewBonusInst->getDebugLoc()) {
1069 // Unless the instruction has the same !dbg location as the original
1070 // branch, drop it. When we fold the bonus instructions we want to make
1071 // sure we reset their debug locations in order to avoid stepping on
1072 // dead code caused by folding dead branches.
1073 NewBonusInst->setDebugLoc(DebugLoc());
1074 }
1075
1076 RemapInstruction(NewBonusInst, VMap,
1077 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
1078 VMap[&BonusInst] = NewBonusInst;
1079
1080 // If we moved a load, we cannot any longer claim any knowledge about
1081 // its potential value. The previous information might have been valid
1082 // only given the branch precondition.
1083 // For an analogous reason, we must also drop all the metadata whose
1084 // semantics we don't understand. We *can* preserve !annotation, because
1085 // it is tied to the instruction itself, not the value or position.
1086 // Similarly strip attributes on call parameters that may cause UB in
1087 // location the call is moved to.
1088 NewBonusInst->dropUndefImplyingAttrsAndUnknownMetadata(
1089 LLVMContext::MD_annotation);
1090
1091 PredBlock->getInstList().insert(PTI->getIterator(), NewBonusInst);
1092 NewBonusInst->takeName(&BonusInst);
1093 BonusInst.setName(NewBonusInst->getName() + ".old");
1094
1095 // Update (liveout) uses of bonus instructions,
1096 // now that the bonus instruction has been cloned into predecessor.
1097 // Note that we expect to be in a block-closed SSA form for this to work!
1098 for (Use &U : make_early_inc_range(BonusInst.uses())) {
1099 auto *UI = cast<Instruction>(U.getUser());
1100 auto *PN = dyn_cast<PHINode>(UI);
1101 if (!PN) {
1102 assert(UI->getParent() == BB && BonusInst.comesBefore(UI) &&((void)0)
1103 "If the user is not a PHI node, then it should be in the same "((void)0)
1104 "block as, and come after, the original bonus instruction.")((void)0);
1105 continue; // Keep using the original bonus instruction.
1106 }
1107 // Is this the block-closed SSA form PHI node?
1108 if (PN->getIncomingBlock(U) == BB)
1109 continue; // Great, keep using the original bonus instruction.
1110 // The only other alternative is an "use" when coming from
1111 // the predecessor block - here we should refer to the cloned bonus instr.
1112 assert(PN->getIncomingBlock(U) == PredBlock &&((void)0)
1113 "Not in block-closed SSA form?")((void)0);
1114 U.set(NewBonusInst);
1115 }
1116 }
1117}
1118
1119bool SimplifyCFGOpt::PerformValueComparisonIntoPredecessorFolding(
1120 Instruction *TI, Value *&CV, Instruction *PTI, IRBuilder<> &Builder) {
1121 BasicBlock *BB = TI->getParent();
1122 BasicBlock *Pred = PTI->getParent();
1123
1124 SmallVector<DominatorTree::UpdateType, 32> Updates;
1125
1126 // Figure out which 'cases' to copy from SI to PSI.
1127 std::vector<ValueEqualityComparisonCase> BBCases;
1128 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
1129
1130 std::vector<ValueEqualityComparisonCase> PredCases;
1131 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
1132
1133 // Based on whether the default edge from PTI goes to BB or not, fill in
1134 // PredCases and PredDefault with the new switch cases we would like to
1135 // build.
1136 SmallMapVector<BasicBlock *, int, 8> NewSuccessors;
1137
1138 // Update the branch weight metadata along the way
1139 SmallVector<uint64_t, 8> Weights;
1140 bool PredHasWeights = HasBranchWeights(PTI);
1141 bool SuccHasWeights = HasBranchWeights(TI);
1142
1143 if (PredHasWeights) {
1144 GetBranchWeights(PTI, Weights);
1145 // branch-weight metadata is inconsistent here.
1146 if (Weights.size() != 1 + PredCases.size())
1147 PredHasWeights = SuccHasWeights = false;
1148 } else if (SuccHasWeights)
1149 // If there are no predecessor weights but there are successor weights,
1150 // populate Weights with 1, which will later be scaled to the sum of
1151 // successor's weights
1152 Weights.assign(1 + PredCases.size(), 1);
1153
1154 SmallVector<uint64_t, 8> SuccWeights;
1155 if (SuccHasWeights) {
1156 GetBranchWeights(TI, SuccWeights);
1157 // branch-weight metadata is inconsistent here.
1158 if (SuccWeights.size() != 1 + BBCases.size())
1159 PredHasWeights = SuccHasWeights = false;
1160 } else if (PredHasWeights)
1161 SuccWeights.assign(1 + BBCases.size(), 1);
1162
1163 if (PredDefault == BB) {
1164 // If this is the default destination from PTI, only the edges in TI
1165 // that don't occur in PTI, or that branch to BB will be activated.
1166 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1167 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1168 if (PredCases[i].Dest != BB)
1169 PTIHandled.insert(PredCases[i].Value);
1170 else {
1171 // The default destination is BB, we don't need explicit targets.
1172 std::swap(PredCases[i], PredCases.back());
1173
1174 if (PredHasWeights || SuccHasWeights) {
1175 // Increase weight for the default case.
1176 Weights[0] += Weights[i + 1];
1177 std::swap(Weights[i + 1], Weights.back());
1178 Weights.pop_back();
1179 }
1180
1181 PredCases.pop_back();
1182 --i;
1183 --e;
1184 }
1185
1186 // Reconstruct the new switch statement we will be building.
1187 if (PredDefault != BBDefault) {
1188 PredDefault->removePredecessor(Pred);
1189 if (DTU && PredDefault != BB)
1190 Updates.push_back({DominatorTree::Delete, Pred, PredDefault});
1191 PredDefault = BBDefault;
1192 ++NewSuccessors[BBDefault];
1193 }
1194
1195 unsigned CasesFromPred = Weights.size();
1196 uint64_t ValidTotalSuccWeight = 0;
1197 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1198 if (!PTIHandled.count(BBCases[i].Value) && BBCases[i].Dest != BBDefault) {
1199 PredCases.push_back(BBCases[i]);
1200 ++NewSuccessors[BBCases[i].Dest];
1201 if (SuccHasWeights || PredHasWeights) {
1202 // The default weight is at index 0, so weight for the ith case
1203 // should be at index i+1. Scale the cases from successor by
1204 // PredDefaultWeight (Weights[0]).
1205 Weights.push_back(Weights[0] * SuccWeights[i + 1]);
1206 ValidTotalSuccWeight += SuccWeights[i + 1];
1207 }
1208 }
1209
1210 if (SuccHasWeights || PredHasWeights) {
1211 ValidTotalSuccWeight += SuccWeights[0];
1212 // Scale the cases from predecessor by ValidTotalSuccWeight.
1213 for (unsigned i = 1; i < CasesFromPred; ++i)
1214 Weights[i] *= ValidTotalSuccWeight;
1215 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
1216 Weights[0] *= SuccWeights[0];
1217 }
1218 } else {
1219 // If this is not the default destination from PSI, only the edges
1220 // in SI that occur in PSI with a destination of BB will be
1221 // activated.
1222 std::set<ConstantInt *, ConstantIntOrdering> PTIHandled;
1223 std::map<ConstantInt *, uint64_t> WeightsForHandled;
1224 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
1225 if (PredCases[i].Dest == BB) {
1226 PTIHandled.insert(PredCases[i].Value);
1227
1228 if (PredHasWeights || SuccHasWeights) {
1229 WeightsForHandled[PredCases[i].Value] = Weights[i + 1];
1230 std::swap(Weights[i + 1], Weights.back());
1231 Weights.pop_back();
1232 }
1233
1234 std::swap(PredCases[i], PredCases.back());
1235 PredCases.pop_back();
1236 --i;
1237 --e;
1238 }
1239
1240 // Okay, now we know which constants were sent to BB from the
1241 // predecessor. Figure out where they will all go now.
1242 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
1243 if (PTIHandled.count(BBCases[i].Value)) {
1244 // If this is one we are capable of getting...
1245 if (PredHasWeights || SuccHasWeights)
1246 Weights.push_back(WeightsForHandled[BBCases[i].Value]);
1247 PredCases.push_back(BBCases[i]);
1248 ++NewSuccessors[BBCases[i].Dest];
1249 PTIHandled.erase(BBCases[i].Value); // This constant is taken care of
1250 }
1251
1252 // If there are any constants vectored to BB that TI doesn't handle,
1253 // they must go to the default destination of TI.
1254 for (ConstantInt *I : PTIHandled) {
1255 if (PredHasWeights || SuccHasWeights)
1256 Weights.push_back(WeightsForHandled[I]);
1257 PredCases.push_back(ValueEqualityComparisonCase(I, BBDefault));
1258 ++NewSuccessors[BBDefault];
1259 }
1260 }
1261
1262 // Okay, at this point, we know which new successor Pred will get. Make
1263 // sure we update the number of entries in the PHI nodes for these
1264 // successors.
1265 SmallPtrSet<BasicBlock *, 2> SuccsOfPred;
1266 if (DTU) {
1267 SuccsOfPred = {succ_begin(Pred), succ_end(Pred)};
1268 Updates.reserve(Updates.size() + NewSuccessors.size());
1269 }
1270 for (const std::pair<BasicBlock *, int /*Num*/> &NewSuccessor :
1271 NewSuccessors) {
1272 for (auto I : seq(0, NewSuccessor.second)) {
1273 (void)I;
1274 AddPredecessorToBlock(NewSuccessor.first, Pred, BB);
1275 }
1276 if (DTU && !SuccsOfPred.contains(NewSuccessor.first))
1277 Updates.push_back({DominatorTree::Insert, Pred, NewSuccessor.first});
1278 }
1279
1280 Builder.SetInsertPoint(PTI);
1281 // Convert pointer to int before we switch.
1282 if (CV->getType()->isPointerTy()) {
1283 CV =
1284 Builder.CreatePtrToInt(CV, DL.getIntPtrType(CV->getType()), "magicptr");
1285 }
1286
1287 // Now that the successors are updated, create the new Switch instruction.
1288 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault, PredCases.size());
1289 NewSI->setDebugLoc(PTI->getDebugLoc());
1290 for (ValueEqualityComparisonCase &V : PredCases)
1291 NewSI->addCase(V.Value, V.Dest);
1292
1293 if (PredHasWeights || SuccHasWeights) {
1294 // Halve the weights if any of them cannot fit in an uint32_t
1295 FitWeights(Weights);
1296
1297 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
1298
1299 setBranchWeights(NewSI, MDWeights);
1300 }
1301
1302 EraseTerminatorAndDCECond(PTI);
1303
1304 // Okay, last check. If BB is still a successor of PSI, then we must
1305 // have an infinite loop case. If so, add an infinitely looping block
1306 // to handle the case to preserve the behavior of the code.
1307 BasicBlock *InfLoopBlock = nullptr;
1308 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
1309 if (NewSI->getSuccessor(i) == BB) {
1310 if (!InfLoopBlock) {
1311 // Insert it at the end of the function, because it's either code,
1312 // or it won't matter if it's hot. :)
1313 InfLoopBlock =
1314 BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
1315 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1316 if (DTU)
1317 Updates.push_back(
1318 {DominatorTree::Insert, InfLoopBlock, InfLoopBlock});
1319 }
1320 NewSI->setSuccessor(i, InfLoopBlock);
1321 }
1322
1323 if (DTU) {
1324 if (InfLoopBlock)
1325 Updates.push_back({DominatorTree::Insert, Pred, InfLoopBlock});
1326
1327 Updates.push_back({DominatorTree::Delete, Pred, BB});
1328
1329 DTU->applyUpdates(Updates);
1330 }
1331
1332 ++NumFoldValueComparisonIntoPredecessors;
1333 return true;
1334}
1335
1336/// The specified terminator is a value equality comparison instruction
1337/// (either a switch or a branch on "X == c").
1338/// See if any of the predecessors of the terminator block are value comparisons
1339/// on the same value. If so, and if safe to do so, fold them together.
1340bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(Instruction *TI,
1341 IRBuilder<> &Builder) {
1342 BasicBlock *BB = TI->getParent();
1343 Value *CV = isValueEqualityComparison(TI); // CondVal
1344 assert(CV && "Not a comparison?")((void)0);
1345
1346 bool Changed = false;
1347
1348 SmallSetVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
1349 while (!Preds.empty()) {
1350 BasicBlock *Pred = Preds.pop_back_val();
1351 Instruction *PTI = Pred->getTerminator();
1352
1353 // Don't try to fold into itself.
1354 if (Pred == BB)
1355 continue;
1356
1357 // See if the predecessor is a comparison with the same value.
1358 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
1359 if (PCV != CV)
1360 continue;
1361
1362 SmallSetVector<BasicBlock *, 4> FailBlocks;
1363 if (!SafeToMergeTerminators(TI, PTI, &FailBlocks)) {
1364 for (auto *Succ : FailBlocks) {
1365 if (!SplitBlockPredecessors(Succ, TI->getParent(), ".fold.split", DTU))
1366 return false;
1367 }
1368 }
1369
1370 PerformValueComparisonIntoPredecessorFolding(TI, CV, PTI, Builder);
1371 Changed = true;
1372 }
1373 return Changed;
1374}
1375
1376// If we would need to insert a select that uses the value of this invoke
1377// (comments in HoistThenElseCodeToIf explain why we would need to do this), we
1378// can't hoist the invoke, as there is nowhere to put the select in this case.
1379static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
1380 Instruction *I1, Instruction *I2) {
1381 for (BasicBlock *Succ : successors(BB1)) {
1382 for (const PHINode &PN : Succ->phis()) {
1383 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1384 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1385 if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) {
1386 return false;
1387 }
1388 }
1389 }
1390 return true;
1391}
1392
1393static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValueMayBeModified = false);
1394
1395/// Given a conditional branch that goes to BB1 and BB2, hoist any common code
1396/// in the two blocks up into the branch block. The caller of this function
1397/// guarantees that BI's block dominates BB1 and BB2. If EqTermsOnly is given,
1398/// only perform hoisting in case both blocks only contain a terminator. In that
1399/// case, only the original BI will be replaced and selects for PHIs are added.
1400bool SimplifyCFGOpt::HoistThenElseCodeToIf(BranchInst *BI,
1401 const TargetTransformInfo &TTI,
1402 bool EqTermsOnly) {
1403 // This does very trivial matching, with limited scanning, to find identical
1404 // instructions in the two blocks. In particular, we don't want to get into
1405 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
1406 // such, we currently just scan for obviously identical instructions in an
1407 // identical order.
1408 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
1409 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
1410
1411 // If either of the blocks has it's address taken, then we can't do this fold,
1412 // because the code we'd hoist would no longer run when we jump into the block
1413 // by it's address.
1414 if (BB1->hasAddressTaken() || BB2->hasAddressTaken())
1415 return false;
1416
1417 BasicBlock::iterator BB1_Itr = BB1->begin();
1418 BasicBlock::iterator BB2_Itr = BB2->begin();
1419
1420 Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
1421 // Skip debug info if it is not identical.
1422 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1423 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1424 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1425 while (isa<DbgInfoIntrinsic>(I1))
1426 I1 = &*BB1_Itr++;
1427 while (isa<DbgInfoIntrinsic>(I2))
1428 I2 = &*BB2_Itr++;
1429 }
1430 // FIXME: Can we define a safety predicate for CallBr?
1431 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
1432 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) ||
1433 isa<CallBrInst>(I1))
1434 return false;
1435
1436 BasicBlock *BIParent = BI->getParent();
1437
1438 bool Changed = false;
1439
1440 auto _ = make_scope_exit([&]() {
1441 if (Changed)
1442 ++NumHoistCommonCode;
1443 });
1444
1445 // Check if only hoisting terminators is allowed. This does not add new
1446 // instructions to the hoist location.
1447 if (EqTermsOnly) {
1448 // Skip any debug intrinsics, as they are free to hoist.
1449 auto *I1NonDbg = &*skipDebugIntrinsics(I1->getIterator());
1450 auto *I2NonDbg = &*skipDebugIntrinsics(I2->getIterator());
1451 if (!I1NonDbg->isIdenticalToWhenDefined(I2NonDbg))
1452 return false;
1453 if (!I1NonDbg->isTerminator())
1454 return false;
1455 // Now we know that we only need to hoist debug instrinsics and the
1456 // terminator. Let the loop below handle those 2 cases.
1457 }
1458
1459 do {
1460 // If we are hoisting the terminator instruction, don't move one (making a
1461 // broken BB), instead clone it, and remove BI.
1462 if (I1->isTerminator())
1463 goto HoistTerminator;
1464
1465 // If we're going to hoist a call, make sure that the two instructions we're
1466 // commoning/hoisting are both marked with musttail, or neither of them is
1467 // marked as such. Otherwise, we might end up in a situation where we hoist
1468 // from a block where the terminator is a `ret` to a block where the terminator
1469 // is a `br`, and `musttail` calls expect to be followed by a return.
1470 auto *C1 = dyn_cast<CallInst>(I1);
1471 auto *C2 = dyn_cast<CallInst>(I2);
1472 if (C1 && C2)
1473 if (C1->isMustTailCall() != C2->isMustTailCall())
1474 return Changed;
1475
1476 if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
1477 return Changed;
1478
1479 // If any of the two call sites has nomerge attribute, stop hoisting.
1480 if (const auto *CB1 = dyn_cast<CallBase>(I1))
1481 if (CB1->cannotMerge())
1482 return Changed;
1483 if (const auto *CB2 = dyn_cast<CallBase>(I2))
1484 if (CB2->cannotMerge())
1485 return Changed;
1486
1487 if (isa<DbgInfoIntrinsic>(I1) || isa<DbgInfoIntrinsic>(I2)) {
1488 assert (isa<DbgInfoIntrinsic>(I1) && isa<DbgInfoIntrinsic>(I2))((void)0);
1489 // The debug location is an integral part of a debug info intrinsic
1490 // and can't be separated from it or replaced. Instead of attempting
1491 // to merge locations, simply hoist both copies of the intrinsic.
1492 BIParent->getInstList().splice(BI->getIterator(),
1493 BB1->getInstList(), I1);
1494 BIParent->getInstList().splice(BI->getIterator(),
1495 BB2->getInstList(), I2);
1496 Changed = true;
1497 } else {
1498 // For a normal instruction, we just move one to right before the branch,
1499 // then replace all uses of the other with the first. Finally, we remove
1500 // the now redundant second instruction.
1501 BIParent->getInstList().splice(BI->getIterator(),
1502 BB1->getInstList(), I1);
1503 if (!I2->use_empty())
1504 I2->replaceAllUsesWith(I1);
1505 I1->andIRFlags(I2);
1506 unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
1507 LLVMContext::MD_range,
1508 LLVMContext::MD_fpmath,
1509 LLVMContext::MD_invariant_load,
1510 LLVMContext::MD_nonnull,
1511 LLVMContext::MD_invariant_group,
1512 LLVMContext::MD_align,
1513 LLVMContext::MD_dereferenceable,
1514 LLVMContext::MD_dereferenceable_or_null,
1515 LLVMContext::MD_mem_parallel_loop_access,
1516 LLVMContext::MD_access_group,
1517 LLVMContext::MD_preserve_access_index};
1518 combineMetadata(I1, I2, KnownIDs, true);
1519
1520 // I1 and I2 are being combined into a single instruction. Its debug
1521 // location is the merged locations of the original instructions.
1522 I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
1523
1524 I2->eraseFromParent();
1525 Changed = true;
1526 }
1527 ++NumHoistCommonInstrs;
1528
1529 I1 = &*BB1_Itr++;
1530 I2 = &*BB2_Itr++;
1531 // Skip debug info if it is not identical.
1532 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
1533 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
1534 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
1535 while (isa<DbgInfoIntrinsic>(I1))
1536 I1 = &*BB1_Itr++;
1537 while (isa<DbgInfoIntrinsic>(I2))
1538 I2 = &*BB2_Itr++;
1539 }
1540 } while (I1->isIdenticalToWhenDefined(I2));
1541
1542 return true;
1543
1544HoistTerminator:
1545 // It may not be possible to hoist an invoke.
1546 // FIXME: Can we define a safety predicate for CallBr?
1547 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
1548 return Changed;
1549
1550 // TODO: callbr hoisting currently disabled pending further study.
1551 if (isa<CallBrInst>(I1))
1552 return Changed;
1553
1554 for (BasicBlock *Succ : successors(BB1)) {
1555 for (PHINode &PN : Succ->phis()) {
1556 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1557 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1558 if (BB1V == BB2V)
1559 continue;
1560
1561 // Check for passingValueIsAlwaysUndefined here because we would rather
1562 // eliminate undefined control flow then converting it to a select.
1563 if (passingValueIsAlwaysUndefined(BB1V, &PN) ||
1564 passingValueIsAlwaysUndefined(BB2V, &PN))
1565 return Changed;
1566
1567 if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
1568 return Changed;
1569 if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
1570 return Changed;
1571 }
1572 }
1573
1574 // Okay, it is safe to hoist the terminator.
1575 Instruction *NT = I1->clone();
1576 BIParent->getInstList().insert(BI->getIterator(), NT);
1577 if (!NT->getType()->isVoidTy()) {
1578 I1->replaceAllUsesWith(NT);
1579 I2->replaceAllUsesWith(NT);
1580 NT->takeName(I1);
1581 }
1582 Changed = true;
1583 ++NumHoistCommonInstrs;
1584
1585 // Ensure terminator gets a debug location, even an unknown one, in case
1586 // it involves inlinable calls.
1587 NT->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
1588
1589 // PHIs created below will adopt NT's merged DebugLoc.
1590 IRBuilder<NoFolder> Builder(NT);
1591
1592 // Hoisting one of the terminators from our successor is a great thing.
1593 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
1594 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
1595 // nodes, so we insert select instruction to compute the final result.
1596 std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects;
1597 for (BasicBlock *Succ : successors(BB1)) {
1598 for (PHINode &PN : Succ->phis()) {
1599 Value *BB1V = PN.getIncomingValueForBlock(BB1);
1600 Value *BB2V = PN.getIncomingValueForBlock(BB2);
1601 if (BB1V == BB2V)
1602 continue;
1603
1604 // These values do not agree. Insert a select instruction before NT
1605 // that determines the right value.
1606 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
1607 if (!SI) {
1608 // Propagate fast-math-flags from phi node to its replacement select.
1609 IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
1610 if (isa<FPMathOperator>(PN))
1611 Builder.setFastMathFlags(PN.getFastMathFlags());
1612
1613 SI = cast<SelectInst>(
1614 Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
1615 BB1V->getName() + "." + BB2V->getName(), BI));
1616 }
1617
1618 // Make the PHI node use the select for all incoming values for BB1/BB2
1619 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
1620 if (PN.getIncomingBlock(i) == BB1 || PN.getIncomingBlock(i) == BB2)
1621 PN.setIncomingValue(i, SI);
1622 }
1623 }
1624
1625 SmallVector<DominatorTree::UpdateType, 4> Updates;
1626
1627 // Update any PHI nodes in our new successors.
1628 for (BasicBlock *Succ : successors(BB1)) {
1629 AddPredecessorToBlock(Succ, BIParent, BB1);
1630 if (DTU)
1631 Updates.push_back({DominatorTree::Insert, BIParent, Succ});
1632 }
1633
1634 if (DTU)
1635 for (BasicBlock *Succ : successors(BI))
1636 Updates.push_back({DominatorTree::Delete, BIParent, Succ});
1637
1638 EraseTerminatorAndDCECond(BI);
1639 if (DTU)
1640 DTU->applyUpdates(Updates);
1641 return Changed;
1642}
1643
1644// Check lifetime markers.
1645static bool isLifeTimeMarker(const Instruction *I) {
1646 if (auto II = dyn_cast<IntrinsicInst>(I)) {
1647 switch (II->getIntrinsicID()) {
1648 default:
1649 break;
1650 case Intrinsic::lifetime_start:
1651 case Intrinsic::lifetime_end:
1652 return true;
1653 }
1654 }
1655 return false;
1656}
1657
1658// TODO: Refine this. This should avoid cases like turning constant memcpy sizes
1659// into variables.
1660static bool replacingOperandWithVariableIsCheap(const Instruction *I,
1661 int OpIdx) {
1662 return !isa<IntrinsicInst>(I);
1663}
1664
1665// All instructions in Insts belong to different blocks that all unconditionally
1666// branch to a common successor. Analyze each instruction and return true if it
1667// would be possible to sink them into their successor, creating one common
1668// instruction instead. For every value that would be required to be provided by
1669// PHI node (because an operand varies in each input block), add to PHIOperands.
1670static bool canSinkInstructions(
1671 ArrayRef<Instruction *> Insts,
1672 DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) {
1673 // Prune out obviously bad instructions to move. Each instruction must have
1674 // exactly zero or one use, and we check later that use is by a single, common
1675 // PHI instruction in the successor.
1676 bool HasUse = !Insts.front()->user_empty();
1677 for (auto *I : Insts) {
1678 // These instructions may change or break semantics if moved.
1679 if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
1680 I->getType()->isTokenTy())
1681 return false;
1682
1683 // Do not try to sink an instruction in an infinite loop - it can cause
1684 // this algorithm to infinite loop.
1685 if (I->getParent()->getSingleSuccessor() == I->getParent())
1686 return false;
1687
1688 // Conservatively return false if I is an inline-asm instruction. Sinking
1689 // and merging inline-asm instructions can potentially create arguments
1690 // that cannot satisfy the inline-asm constraints.
1691 // If the instruction has nomerge attribute, return false.
1692 if (const auto *C = dyn_cast<CallBase>(I))
1693 if (C->isInlineAsm() || C->cannotMerge())
1694 return false;
1695
1696 // Each instruction must have zero or one use.
1697 if (HasUse && !I->hasOneUse())
1698 return false;
1699 if (!HasUse && !I->user_empty())
1700 return false;
1701 }
1702
1703 const Instruction *I0 = Insts.front();
1704 for (auto *I : Insts)
1705 if (!I->isSameOperationAs(I0))
1706 return false;
1707
1708 // All instructions in Insts are known to be the same opcode. If they have a
1709 // use, check that the only user is a PHI or in the same block as the
1710 // instruction, because if a user is in the same block as an instruction we're
1711 // contemplating sinking, it must already be determined to be sinkable.
1712 if (HasUse) {
1713 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1714 auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0);
1715 if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool {
1716 auto *U = cast<Instruction>(*I->user_begin());
1717 return (PNUse &&
1718 PNUse->getParent() == Succ &&
1719 PNUse->getIncomingValueForBlock(I->getParent()) == I) ||
1720 U->getParent() == I->getParent();
1721 }))
1722 return false;
1723 }
1724
1725 // Because SROA can't handle speculating stores of selects, try not to sink
1726 // loads, stores or lifetime markers of allocas when we'd have to create a
1727 // PHI for the address operand. Also, because it is likely that loads or
1728 // stores of allocas will disappear when Mem2Reg/SROA is run, don't sink
1729 // them.
1730 // This can cause code churn which can have unintended consequences down
1731 // the line - see https://llvm.org/bugs/show_bug.cgi?id=30244.
1732 // FIXME: This is a workaround for a deficiency in SROA - see
1733 // https://llvm.org/bugs/show_bug.cgi?id=30188
1734 if (isa<StoreInst>(I0) && any_of(Insts, [](const Instruction *I) {
1735 return isa<AllocaInst>(I->getOperand(1)->stripPointerCasts());
1736 }))
1737 return false;
1738 if (isa<LoadInst>(I0) && any_of(Insts, [](const Instruction *I) {
1739 return isa<AllocaInst>(I->getOperand(0)->stripPointerCasts());
1740 }))
1741 return false;
1742 if (isLifeTimeMarker(I0) && any_of(Insts, [](const Instruction *I) {
1743 return isa<AllocaInst>(I->getOperand(1)->stripPointerCasts());
1744 }))
1745 return false;
1746
1747 // For calls to be sinkable, they must all be indirect, or have same callee.
1748 // I.e. if we have two direct calls to different callees, we don't want to
1749 // turn that into an indirect call. Likewise, if we have an indirect call,
1750 // and a direct call, we don't actually want to have a single indirect call.
1751 if (isa<CallBase>(I0)) {
1752 auto IsIndirectCall = [](const Instruction *I) {
1753 return cast<CallBase>(I)->isIndirectCall();
1754 };
1755 bool HaveIndirectCalls = any_of(Insts, IsIndirectCall);
1756 bool AllCallsAreIndirect = all_of(Insts, IsIndirectCall);
1757 if (HaveIndirectCalls) {
1758 if (!AllCallsAreIndirect)
1759 return false;
1760 } else {
1761 // All callees must be identical.
1762 Value *Callee = nullptr;
1763 for (const Instruction *I : Insts) {
1764 Value *CurrCallee = cast<CallBase>(I)->getCalledOperand();
1765 if (!Callee)
1766 Callee = CurrCallee;
1767 else if (Callee != CurrCallee)
1768 return false;
1769 }
1770 }
1771 }
1772
1773 for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) {
1774 Value *Op = I0->getOperand(OI);
1775 if (Op->getType()->isTokenTy())
1776 // Don't touch any operand of token type.
1777 return false;
1778
1779 auto SameAsI0 = [&I0, OI](const Instruction *I) {
1780 assert(I->getNumOperands() == I0->getNumOperands())((void)0);
1781 return I->getOperand(OI) == I0->getOperand(OI);
1782 };
1783 if (!all_of(Insts, SameAsI0)) {
1784 if ((isa<Constant>(Op) && !replacingOperandWithVariableIsCheap(I0, OI)) ||
1785 !canReplaceOperandWithVariable(I0, OI))
1786 // We can't create a PHI from this GEP.
1787 return false;
1788 for (auto *I : Insts)
1789 PHIOperands[I].push_back(I->getOperand(OI));
1790 }
1791 }
1792 return true;
1793}
1794
1795// Assuming canSinkInstructions(Blocks) has returned true, sink the last
1796// instruction of every block in Blocks to their common successor, commoning
1797// into one instruction.
1798static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
1799 auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0);
1800
1801 // canSinkInstructions returning true guarantees that every block has at
1802 // least one non-terminator instruction.
1803 SmallVector<Instruction*,4> Insts;
1804 for (auto *BB : Blocks) {
1805 Instruction *I = BB->getTerminator();
1806 do {
1807 I = I->getPrevNode();
1808 } while (isa<DbgInfoIntrinsic>(I) && I != &BB->front());
1809 if (!isa<DbgInfoIntrinsic>(I))
1810 Insts.push_back(I);
1811 }
1812
1813 // The only checking we need to do now is that all users of all instructions
1814 // are the same PHI node. canSinkInstructions should have checked this but
1815 // it is slightly over-aggressive - it gets confused by commutative
1816 // instructions so double-check it here.
1817 Instruction *I0 = Insts.front();
1818 if (!I0->user_empty()) {
1819 auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
1820 if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
1821 auto *U = cast<Instruction>(*I->user_begin());
1822 return U == PNUse;
1823 }))
1824 return false;
1825 }
1826
1827 // We don't need to do any more checking here; canSinkInstructions should
1828 // have done it all for us.
1829 SmallVector<Value*, 4> NewOperands;
1830 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
1831 // This check is different to that in canSinkInstructions. There, we
1832 // cared about the global view once simplifycfg (and instcombine) have
1833 // completed - it takes into account PHIs that become trivially
1834 // simplifiable. However here we need a more local view; if an operand
1835 // differs we create a PHI and rely on instcombine to clean up the very
1836 // small mess we may make.
1837 bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) {
1838 return I->getOperand(O) != I0->getOperand(O);
1839 });
1840 if (!NeedPHI) {
1841 NewOperands.push_back(I0->getOperand(O));
1842 continue;
1843 }
1844
1845 // Create a new PHI in the successor block and populate it.
1846 auto *Op = I0->getOperand(O);
1847 assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!")((void)0);
1848 auto *PN = PHINode::Create(Op->getType(), Insts.size(),
1849 Op->getName() + ".sink", &BBEnd->front());
1850 for (auto *I : Insts)
1851 PN->addIncoming(I->getOperand(O), I->getParent());
1852 NewOperands.push_back(PN);
1853 }
1854
1855 // Arbitrarily use I0 as the new "common" instruction; remap its operands
1856 // and move it to the start of the successor block.
1857 for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
1858 I0->getOperandUse(O).set(NewOperands[O]);
1859 I0->moveBefore(&*BBEnd->getFirstInsertionPt());
1860
1861 // Update metadata and IR flags, and merge debug locations.
1862 for (auto *I : Insts)
1863 if (I != I0) {
1864 // The debug location for the "common" instruction is the merged locations
1865 // of all the commoned instructions. We start with the original location
1866 // of the "common" instruction and iteratively merge each location in the
1867 // loop below.
1868 // This is an N-way merge, which will be inefficient if I0 is a CallInst.
1869 // However, as N-way merge for CallInst is rare, so we use simplified API
1870 // instead of using complex API for N-way merge.
1871 I0->applyMergedLocation(I0->getDebugLoc(), I->getDebugLoc());
1872 combineMetadataForCSE(I0, I, true);
1873 I0->andIRFlags(I);
1874 }
1875
1876 if (!I0->user_empty()) {
1877 // canSinkLastInstruction checked that all instructions were used by
1878 // one and only one PHI node. Find that now, RAUW it to our common
1879 // instruction and nuke it.
1880 auto *PN = cast<PHINode>(*I0->user_begin());
1881 PN->replaceAllUsesWith(I0);
1882 PN->eraseFromParent();
1883 }
1884
1885 // Finally nuke all instructions apart from the common instruction.
1886 for (auto *I : Insts)
1887 if (I != I0)
1888 I->eraseFromParent();
1889
1890 return true;
1891}
1892
1893namespace {
1894
1895 // LockstepReverseIterator - Iterates through instructions
1896 // in a set of blocks in reverse order from the first non-terminator.
1897 // For example (assume all blocks have size n):
1898 // LockstepReverseIterator I([B1, B2, B3]);
1899 // *I-- = [B1[n], B2[n], B3[n]];
1900 // *I-- = [B1[n-1], B2[n-1], B3[n-1]];
1901 // *I-- = [B1[n-2], B2[n-2], B3[n-2]];
1902 // ...
1903 class LockstepReverseIterator {
1904 ArrayRef<BasicBlock*> Blocks;
1905 SmallVector<Instruction*,4> Insts;
1906 bool Fail;
1907
1908 public:
1909 LockstepReverseIterator(ArrayRef<BasicBlock*> Blocks) : Blocks(Blocks) {
1910 reset();
1911 }
1912
1913 void reset() {
1914 Fail = false;
1915 Insts.clear();
1916 for (auto *BB : Blocks) {
1917 Instruction *Inst = BB->getTerminator();
1918 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1919 Inst = Inst->getPrevNode();
1920 if (!Inst) {
1921 // Block wasn't big enough.
1922 Fail = true;
1923 return;
1924 }
1925 Insts.push_back(Inst);
1926 }
1927 }
1928
1929 bool isValid() const {
1930 return !Fail;
1931 }
1932
1933 void operator--() {
1934 if (Fail)
1935 return;
1936 for (auto *&Inst : Insts) {
1937 for (Inst = Inst->getPrevNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1938 Inst = Inst->getPrevNode();
1939 // Already at beginning of block.
1940 if (!Inst) {
1941 Fail = true;
1942 return;
1943 }
1944 }
1945 }
1946
1947 void operator++() {
1948 if (Fail)
1949 return;
1950 for (auto *&Inst : Insts) {
1951 for (Inst = Inst->getNextNode(); Inst && isa<DbgInfoIntrinsic>(Inst);)
1952 Inst = Inst->getNextNode();
1953 // Already at end of block.
1954 if (!Inst) {
1955 Fail = true;
1956 return;
1957 }
1958 }
1959 }
1960
1961 ArrayRef<Instruction*> operator * () const {
1962 return Insts;
1963 }
1964 };
1965
1966} // end anonymous namespace
1967
1968/// Check whether BB's predecessors end with unconditional branches. If it is
1969/// true, sink any common code from the predecessors to BB.
1970static bool SinkCommonCodeFromPredecessors(BasicBlock *BB,
1971 DomTreeUpdater *DTU) {
1972 // We support two situations:
1973 // (1) all incoming arcs are unconditional
1974 // (2) there are non-unconditional incoming arcs
1975 //
1976 // (2) is very common in switch defaults and
1977 // else-if patterns;
1978 //
1979 // if (a) f(1);
1980 // else if (b) f(2);
1981 //
1982 // produces:
1983 //
1984 // [if]
1985 // / \
1986 // [f(1)] [if]
1987 // | | \
1988 // | | |
1989 // | [f(2)]|
1990 // \ | /
1991 // [ end ]
1992 //
1993 // [end] has two unconditional predecessor arcs and one conditional. The
1994 // conditional refers to the implicit empty 'else' arc. This conditional
1995 // arc can also be caused by an empty default block in a switch.
1996 //
1997 // In this case, we attempt to sink code from all *unconditional* arcs.
1998 // If we can sink instructions from these arcs (determined during the scan
1999 // phase below) we insert a common successor for all unconditional arcs and
2000 // connect that to [end], to enable sinking:
2001 //
2002 // [if]
2003 // / \
2004 // [x(1)] [if]
2005 // | | \
2006 // | | \
2007 // | [x(2)] |
2008 // \ / |
2009 // [sink.split] |
2010 // \ /
2011 // [ end ]
2012 //
2013 SmallVector<BasicBlock*,4> UnconditionalPreds;
2014 bool HaveNonUnconditionalPredecessors = false;
2015 for (auto *PredBB : predecessors(BB)) {
2016 auto *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
2017 if (PredBr && PredBr->isUnconditional())
2018 UnconditionalPreds.push_back(PredBB);
2019 else
2020 HaveNonUnconditionalPredecessors = true;
2021 }
2022 if (UnconditionalPreds.size() < 2)
2023 return false;
2024
2025 // We take a two-step approach to tail sinking. First we scan from the end of
2026 // each block upwards in lockstep. If the n'th instruction from the end of each
2027 // block can be sunk, those instructions are added to ValuesToSink and we
2028 // carry on. If we can sink an instruction but need to PHI-merge some operands
2029 // (because they're not identical in each instruction) we add these to
2030 // PHIOperands.
2031 int ScanIdx = 0;
2032 SmallPtrSet<Value*,4> InstructionsToSink;
2033 DenseMap<Instruction*, SmallVector<Value*,4>> PHIOperands;
2034 LockstepReverseIterator LRI(UnconditionalPreds);
2035 while (LRI.isValid() &&
2036 canSinkInstructions(*LRI, PHIOperands)) {
2037 LLVM_DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0]do { } while (false)
2038 << "\n")do { } while (false);
2039 InstructionsToSink.insert((*LRI).begin(), (*LRI).end());
2040 ++ScanIdx;
2041 --LRI;
2042 }
2043
2044 // If no instructions can be sunk, early-return.
2045 if (ScanIdx == 0)
2046 return false;
2047
2048 // Okay, we *could* sink last ScanIdx instructions. But how many can we
2049 // actually sink before encountering instruction that is unprofitable to sink?
2050 auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) {
2051 unsigned NumPHIdValues = 0;
2052 for (auto *I : *LRI)
2053 for (auto *V : PHIOperands[I]) {
2054 if (InstructionsToSink.count(V) == 0)
2055 ++NumPHIdValues;
2056 // FIXME: this check is overly optimistic. We may end up not sinking
2057 // said instruction, due to the very same profitability check.
2058 // See @creating_too_many_phis in sink-common-code.ll.
2059 }
2060 LLVM_DEBUG(dbgs() << "SINK: #phid values: " << NumPHIdValues << "\n")do { } while (false);
2061 unsigned NumPHIInsts = NumPHIdValues / UnconditionalPreds.size();
2062 if ((NumPHIdValues % UnconditionalPreds.size()) != 0)
2063 NumPHIInsts++;
2064
2065 return NumPHIInsts <= 1;
2066 };
2067
2068 // We've determined that we are going to sink last ScanIdx instructions,
2069 // and recorded them in InstructionsToSink. Now, some instructions may be
2070 // unprofitable to sink. But that determination depends on the instructions
2071 // that we are going to sink.
2072
2073 // First, forward scan: find the first instruction unprofitable to sink,
2074 // recording all the ones that are profitable to sink.
2075 // FIXME: would it be better, after we detect that not all are profitable.
2076 // to either record the profitable ones, or erase the unprofitable ones?
2077 // Maybe we need to choose (at runtime) the one that will touch least instrs?
2078 LRI.reset();
2079 int Idx = 0;
2080 SmallPtrSet<Value *, 4> InstructionsProfitableToSink;
2081 while (Idx < ScanIdx) {
2082 if (!ProfitableToSinkInstruction(LRI)) {
2083 // Too many PHIs would be created.
2084 LLVM_DEBUG(do { } while (false)
2085 dbgs() << "SINK: stopping here, too many PHIs would be created!\n")do { } while (false);
2086 break;
2087 }
2088 InstructionsProfitableToSink.insert((*LRI).begin(), (*LRI).end());
2089 --LRI;
2090 ++Idx;
2091 }
2092
2093 // If no instructions can be sunk, early-return.
2094 if (Idx == 0)
2095 return false;
2096
2097 // Did we determine that (only) some instructions are unprofitable to sink?
2098 if (Idx < ScanIdx) {
2099 // Okay, some instructions are unprofitable.
2100 ScanIdx = Idx;
2101 InstructionsToSink = InstructionsProfitableToSink;
2102
2103 // But, that may make other instructions unprofitable, too.
2104 // So, do a backward scan, do any earlier instructions become unprofitable?
2105 assert(!ProfitableToSinkInstruction(LRI) &&((void)0)
2106 "We already know that the last instruction is unprofitable to sink")((void)0);
2107 ++LRI;
2108 --Idx;
2109 while (Idx >= 0) {
2110 // If we detect that an instruction becomes unprofitable to sink,
2111 // all earlier instructions won't be sunk either,
2112 // so preemptively keep InstructionsProfitableToSink in sync.
2113 // FIXME: is this the most performant approach?
2114 for (auto *I : *LRI)
2115 InstructionsProfitableToSink.erase(I);
2116 if (!ProfitableToSinkInstruction(LRI)) {
2117 // Everything starting with this instruction won't be sunk.
2118 ScanIdx = Idx;
2119 InstructionsToSink = InstructionsProfitableToSink;
2120 }
2121 ++LRI;
2122 --Idx;
2123 }
2124 }
2125
2126 // If no instructions can be sunk, early-return.
2127 if (ScanIdx == 0)
2128 return false;
2129
2130 bool Changed = false;
2131
2132 if (HaveNonUnconditionalPredecessors) {
2133 // It is always legal to sink common instructions from unconditional
2134 // predecessors. However, if not all predecessors are unconditional,
2135 // this transformation might be pessimizing. So as a rule of thumb,
2136 // don't do it unless we'd sink at least one non-speculatable instruction.
2137 // See https://bugs.llvm.org/show_bug.cgi?id=30244
2138 LRI.reset();
2139 int Idx = 0;
2140 bool Profitable = false;
2141 while (Idx < ScanIdx) {
2142 if (!isSafeToSpeculativelyExecute((*LRI)[0])) {
2143 Profitable = true;
2144 break;
2145 }
2146 --LRI;
2147 ++Idx;
2148 }
2149 if (!Profitable)
2150 return false;
2151
2152 LLVM_DEBUG(dbgs() << "SINK: Splitting edge\n")do { } while (false);
2153 // We have a conditional edge and we're going to sink some instructions.
2154 // Insert a new block postdominating all blocks we're going to sink from.
2155 if (!SplitBlockPredecessors(BB, UnconditionalPreds, ".sink.split", DTU))
2156 // Edges couldn't be split.
2157 return false;
2158 Changed = true;
2159 }
2160
2161 // Now that we've analyzed all potential sinking candidates, perform the
2162 // actual sink. We iteratively sink the last non-terminator of the source
2163 // blocks into their common successor unless doing so would require too
2164 // many PHI instructions to be generated (currently only one PHI is allowed
2165 // per sunk instruction).
2166 //
2167 // We can use InstructionsToSink to discount values needing PHI-merging that will
2168 // actually be sunk in a later iteration. This allows us to be more
2169 // aggressive in what we sink. This does allow a false positive where we
2170 // sink presuming a later value will also be sunk, but stop half way through
2171 // and never actually sink it which means we produce more PHIs than intended.
2172 // This is unlikely in practice though.
2173 int SinkIdx = 0;
2174 for (; SinkIdx != ScanIdx; ++SinkIdx) {
2175 LLVM_DEBUG(dbgs() << "SINK: Sink: "do { } while (false)
2176 << *UnconditionalPreds[0]->getTerminator()->getPrevNode()do { } while (false)
2177 << "\n")do { } while (false);
2178
2179 // Because we've sunk every instruction in turn, the current instruction to
2180 // sink is always at index 0.
2181 LRI.reset();
2182
2183 if (!sinkLastInstruction(UnconditionalPreds)) {
2184 LLVM_DEBUG(do { } while (false)
2185 dbgs()do { } while (false)
2186 << "SINK: stopping here, failed to actually sink instruction!\n")do { } while (false);
2187 break;
2188 }
2189
2190 NumSinkCommonInstrs++;
2191 Changed = true;
2192 }
2193 if (SinkIdx != 0)
2194 ++NumSinkCommonCode;
2195 return Changed;
2196}
2197
2198/// Determine if we can hoist sink a sole store instruction out of a
2199/// conditional block.
2200///
2201/// We are looking for code like the following:
2202/// BrBB:
2203/// store i32 %add, i32* %arrayidx2
2204/// ... // No other stores or function calls (we could be calling a memory
2205/// ... // function).
2206/// %cmp = icmp ult %x, %y
2207/// br i1 %cmp, label %EndBB, label %ThenBB
2208/// ThenBB:
2209/// store i32 %add5, i32* %arrayidx2
2210/// br label EndBB
2211/// EndBB:
2212/// ...
2213/// We are going to transform this into:
2214/// BrBB:
2215/// store i32 %add, i32* %arrayidx2
2216/// ... //
2217/// %cmp = icmp ult %x, %y
2218/// %add.add5 = select i1 %cmp, i32 %add, %add5
2219/// store i32 %add.add5, i32* %arrayidx2
2220/// ...
2221///
2222/// \return The pointer to the value of the previous store if the store can be
2223/// hoisted into the predecessor block. 0 otherwise.
2224static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
2225 BasicBlock *StoreBB, BasicBlock *EndBB) {
2226 StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
2227 if (!StoreToHoist)
2228 return nullptr;
2229
2230 // Volatile or atomic.
2231 if (!StoreToHoist->isSimple())
2232 return nullptr;
2233
2234 Value *StorePtr = StoreToHoist->getPointerOperand();
2235 Type *StoreTy = StoreToHoist->getValueOperand()->getType();
2236
2237 // Look for a store to the same pointer in BrBB.
2238 unsigned MaxNumInstToLookAt = 9;
2239 // Skip pseudo probe intrinsic calls which are not really killing any memory
2240 // accesses.
2241 for (Instruction &CurI : reverse(BrBB->instructionsWithoutDebug(true))) {
2242 if (!MaxNumInstToLookAt)
2243 break;
2244 --MaxNumInstToLookAt;
2245
2246 // Could be calling an instruction that affects memory like free().
2247 if (CurI.mayWriteToMemory() && !isa<StoreInst>(CurI))
2248 return nullptr;
2249
2250 if (auto *SI = dyn_cast<StoreInst>(&CurI)) {
2251 // Found the previous store to same location and type. Make sure it is
2252 // simple, to avoid introducing a spurious non-atomic write after an
2253 // atomic write.
2254 if (SI->getPointerOperand() == StorePtr &&
2255 SI->getValueOperand()->getType() == StoreTy && SI->isSimple())
2256 // Found the previous store, return its value operand.
2257 return SI->getValueOperand();
2258 return nullptr; // Unknown store.
2259 }
2260 }
2261
2262 return nullptr;
2263}
2264
2265/// Estimate the cost of the insertion(s) and check that the PHI nodes can be
2266/// converted to selects.
2267static bool validateAndCostRequiredSelects(BasicBlock *BB, BasicBlock *ThenBB,
2268 BasicBlock *EndBB,
2269 unsigned &SpeculatedInstructions,
2270 InstructionCost &Cost,
2271 const TargetTransformInfo &TTI) {
2272 TargetTransformInfo::TargetCostKind CostKind =
2273 BB->getParent()->hasMinSize()
2274 ? TargetTransformInfo::TCK_CodeSize
2275 : TargetTransformInfo::TCK_SizeAndLatency;
2276
2277 bool HaveRewritablePHIs = false;
2278 for (PHINode &PN : EndBB->phis()) {
2279 Value *OrigV = PN.getIncomingValueForBlock(BB);
2280 Value *ThenV = PN.getIncomingValueForBlock(ThenBB);
2281
2282 // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
2283 // Skip PHIs which are trivial.
2284 if (ThenV == OrigV)
2285 continue;
2286
2287 Cost += TTI.getCmpSelInstrCost(Instruction::Select, PN.getType(), nullptr,
2288 CmpInst::BAD_ICMP_PREDICATE, CostKind);
2289
2290 // Don't convert to selects if we could remove undefined behavior instead.
2291 if (passingValueIsAlwaysUndefined(OrigV, &PN) ||
2292 passingValueIsAlwaysUndefined(ThenV, &PN))
2293 return false;
2294
2295 HaveRewritablePHIs = true;
2296 ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
2297 ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
2298 if (!OrigCE && !ThenCE)
2299 continue; // Known safe and cheap.
2300
2301 if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
2302 (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
2303 return false;
2304 InstructionCost OrigCost = OrigCE ? computeSpeculationCost(OrigCE, TTI) : 0;
2305 InstructionCost ThenCost = ThenCE ? computeSpeculationCost(ThenCE, TTI) : 0;
2306 InstructionCost MaxCost =
2307 2 * PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
2308 if (OrigCost + ThenCost > MaxCost)
2309 return false;
2310
2311 // Account for the cost of an unfolded ConstantExpr which could end up
2312 // getting expanded into Instructions.
2313 // FIXME: This doesn't account for how many operations are combined in the
2314 // constant expression.
2315 ++SpeculatedInstructions;
2316 if (SpeculatedInstructions > 1)
2317 return false;
2318 }
2319
2320 return HaveRewritablePHIs;
2321}
2322
2323/// Speculate a conditional basic block flattening the CFG.
2324///
2325/// Note that this is a very risky transform currently. Speculating
2326/// instructions like this is most often not desirable. Instead, there is an MI
2327/// pass which can do it with full awareness of the resource constraints.
2328/// However, some cases are "obvious" and we should do directly. An example of
2329/// this is speculating a single, reasonably cheap instruction.
2330///
2331/// There is only one distinct advantage to flattening the CFG at the IR level:
2332/// it makes very common but simplistic optimizations such as are common in
2333/// instcombine and the DAG combiner more powerful by removing CFG edges and
2334/// modeling their effects with easier to reason about SSA value graphs.
2335///
2336///
2337/// An illustration of this transform is turning this IR:
2338/// \code
2339/// BB:
2340/// %cmp = icmp ult %x, %y
2341/// br i1 %cmp, label %EndBB, label %ThenBB
2342/// ThenBB:
2343/// %sub = sub %x, %y
2344/// br label BB2
2345/// EndBB:
2346/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ]
2347/// ...
2348/// \endcode
2349///
2350/// Into this IR:
2351/// \code
2352/// BB:
2353/// %cmp = icmp ult %x, %y
2354/// %sub = sub %x, %y
2355/// %cond = select i1 %cmp, 0, %sub
2356/// ...
2357/// \endcode
2358///
2359/// \returns true if the conditional block is removed.
2360bool SimplifyCFGOpt::SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
2361 const TargetTransformInfo &TTI) {
2362 // Be conservative for now. FP select instruction can often be expensive.
2363 Value *BrCond = BI->getCondition();
2364 if (isa<FCmpInst>(BrCond))
2365 return false;
2366
2367 BasicBlock *BB = BI->getParent();
2368 BasicBlock *EndBB = ThenBB->getTerminator()->getSuccessor(0);
2369 InstructionCost Budget =
2370 PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
2371
2372 // If ThenBB is actually on the false edge of the conditional branch, remember
2373 // to swap the select operands later.
2374 bool Invert = false;
2375 if (ThenBB != BI->getSuccessor(0)) {
2376 assert(ThenBB == BI->getSuccessor(1) && "No edge from 'if' block?")((void)0);
2377 Invert = true;
2378 }
2379 assert(EndBB == BI->getSuccessor(!Invert) && "No edge from to end block")((void)0);
2380
2381 // If the branch is non-unpredictable, and is predicted to *not* branch to
2382 // the `then` block, then avoid speculating it.
2383 if (!BI->getMetadata(LLVMContext::MD_unpredictable)) {
2384 uint64_t TWeight, FWeight;
2385 if (BI->extractProfMetadata(TWeight, FWeight) && (TWeight + FWeight) != 0) {
2386 uint64_t EndWeight = Invert ? TWeight : FWeight;
2387 BranchProbability BIEndProb =
2388 BranchProbability::getBranchProbability(EndWeight, TWeight + FWeight);
2389 BranchProbability Likely = TTI.getPredictableBranchThreshold();
2390 if (BIEndProb >= Likely)
2391 return false;
2392 }
2393 }
2394
2395 // Keep a count of how many times instructions are used within ThenBB when
2396 // they are candidates for sinking into ThenBB. Specifically:
2397 // - They are defined in BB, and
2398 // - They have no side effects, and
2399 // - All of their uses are in ThenBB.
2400 SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
2401
2402 SmallVector<Instruction *, 4> SpeculatedDbgIntrinsics;
2403
2404 unsigned SpeculatedInstructions = 0;
2405 Value *SpeculatedStoreValue = nullptr;
2406 StoreInst *SpeculatedStore = nullptr;
2407 for (BasicBlock::iterator BBI = ThenBB->begin(),
2408 BBE = std::prev(ThenBB->end());
2409 BBI != BBE; ++BBI) {
2410 Instruction *I = &*BBI;
2411 // Skip debug info.
2412 if (isa<DbgInfoIntrinsic>(I)) {
2413 SpeculatedDbgIntrinsics.push_back(I);
2414 continue;
2415 }
2416
2417 // Skip pseudo probes. The consequence is we lose track of the branch
2418 // probability for ThenBB, which is fine since the optimization here takes
2419 // place regardless of the branch probability.
2420 if (isa<PseudoProbeInst>(I)) {
2421 // The probe should be deleted so that it will not be over-counted when
2422 // the samples collected on the non-conditional path are counted towards
2423 // the conditional path. We leave it for the counts inference algorithm to
2424 // figure out a proper count for an unknown probe.
2425 SpeculatedDbgIntrinsics.push_back(I);
2426 continue;
2427 }
2428
2429 // Only speculatively execute a single instruction (not counting the
2430 // terminator) for now.
2431 ++SpeculatedInstructions;
2432 if (SpeculatedInstructions > 1)
2433 return false;
2434
2435 // Don't hoist the instruction if it's unsafe or expensive.
2436 if (!isSafeToSpeculativelyExecute(I) &&
2437 !(HoistCondStores && (SpeculatedStoreValue = isSafeToSpeculateStore(
2438 I, BB, ThenBB, EndBB))))
2439 return false;
2440 if (!SpeculatedStoreValue &&
2441 computeSpeculationCost(I, TTI) >
2442 PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic)
2443 return false;
2444
2445 // Store the store speculation candidate.
2446 if (SpeculatedStoreValue)
2447 SpeculatedStore = cast<StoreInst>(I);
2448
2449 // Do not hoist the instruction if any of its operands are defined but not
2450 // used in BB. The transformation will prevent the operand from
2451 // being sunk into the use block.
2452 for (Use &Op : I->operands()) {
2453 Instruction *OpI = dyn_cast<Instruction>(Op);
2454 if (!OpI || OpI->getParent() != BB || OpI->mayHaveSideEffects())
2455 continue; // Not a candidate for sinking.
2456
2457 ++SinkCandidateUseCounts[OpI];
2458 }
2459 }
2460
2461 // Consider any sink candidates which are only used in ThenBB as costs for
2462 // speculation. Note, while we iterate over a DenseMap here, we are summing
2463 // and so iteration order isn't significant.
2464 for (SmallDenseMap<Instruction *, unsigned, 4>::iterator
2465 I = SinkCandidateUseCounts.begin(),
2466 E = SinkCandidateUseCounts.end();
2467 I != E; ++I)
2468 if (I->first->hasNUses(I->second)) {
2469 ++SpeculatedInstructions;
2470 if (SpeculatedInstructions > 1)
2471 return false;
2472 }
2473
2474 // Check that we can insert the selects and that it's not too expensive to do
2475 // so.
2476 bool Convert = SpeculatedStore != nullptr;
2477 InstructionCost Cost = 0;
2478 Convert |= validateAndCostRequiredSelects(BB, ThenBB, EndBB,
2479 SpeculatedInstructions,
2480 Cost, TTI);
2481 if (!Convert || Cost > Budget)
2482 return false;
2483
2484 // If we get here, we can hoist the instruction and if-convert.
2485 LLVM_DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";)do { } while (false);
2486
2487 // Insert a select of the value of the speculated store.
2488 if (SpeculatedStoreValue) {
2489 IRBuilder<NoFolder> Builder(BI);
2490 Value *TrueV = SpeculatedStore->getValueOperand();
2491 Value *FalseV = SpeculatedStoreValue;
2492 if (Invert)
2493 std::swap(TrueV, FalseV);
2494 Value *S = Builder.CreateSelect(
2495 BrCond, TrueV, FalseV, "spec.store.select", BI);
2496 SpeculatedStore->setOperand(0, S);
2497 SpeculatedStore->applyMergedLocation(BI->getDebugLoc(),
2498 SpeculatedStore->getDebugLoc());
2499 }
2500
2501 // Metadata can be dependent on the condition we are hoisting above.
2502 // Conservatively strip all metadata on the instruction. Drop the debug loc
2503 // to avoid making it appear as if the condition is a constant, which would
2504 // be misleading while debugging.
2505 // Similarly strip attributes that maybe dependent on condition we are
2506 // hoisting above.
2507 for (auto &I : *ThenBB) {
2508 if (!SpeculatedStoreValue || &I != SpeculatedStore)
2509 I.setDebugLoc(DebugLoc());
2510 I.dropUndefImplyingAttrsAndUnknownMetadata();
2511 }
2512
2513 // Hoist the instructions.
2514 BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
2515 ThenBB->begin(), std::prev(ThenBB->end()));
2516
2517 // Insert selects and rewrite the PHI operands.
2518 IRBuilder<NoFolder> Builder(BI);
2519 for (PHINode &PN : EndBB->phis()) {
2520 unsigned OrigI = PN.getBasicBlockIndex(BB);
2521 unsigned ThenI = PN.getBasicBlockIndex(ThenBB);
2522 Value *OrigV = PN.getIncomingValue(OrigI);
2523 Value *ThenV = PN.getIncomingValue(ThenI);
2524
2525 // Skip PHIs which are trivial.
2526 if (OrigV == ThenV)
2527 continue;
2528
2529 // Create a select whose true value is the speculatively executed value and
2530 // false value is the pre-existing value. Swap them if the branch
2531 // destinations were inverted.
2532 Value *TrueV = ThenV, *FalseV = OrigV;
2533 if (Invert)
2534 std::swap(TrueV, FalseV);
2535 Value *V = Builder.CreateSelect(BrCond, TrueV, FalseV, "spec.select", BI);
2536 PN.setIncomingValue(OrigI, V);
2537 PN.setIncomingValue(ThenI, V);
2538 }
2539
2540 // Remove speculated dbg intrinsics.
2541 // FIXME: Is it possible to do this in a more elegant way? Moving/merging the
2542 // dbg value for the different flows and inserting it after the select.
2543 for (Instruction *I : SpeculatedDbgIntrinsics)
2544 I->eraseFromParent();
2545
2546 ++NumSpeculations;
2547 return true;
2548}
2549
2550/// Return true if we can thread a branch across this block.
2551static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
2552 int Size = 0;
2553
2554 SmallPtrSet<const Value *, 32> EphValues;
2555 auto IsEphemeral = [&](const Value *V) {
2556 if (isa<AssumeInst>(V))
2557 return true;
2558 return isSafeToSpeculativelyExecute(V) &&
2559 all_of(V->users(),
2560 [&](const User *U) { return EphValues.count(U); });
2561 };
2562
2563 // Walk the loop in reverse so that we can identify ephemeral values properly
2564 // (values only feeding assumes).
2565 for (Instruction &I : reverse(BB->instructionsWithoutDebug())) {
2566 // Can't fold blocks that contain noduplicate or convergent calls.
2567 if (CallInst *CI = dyn_cast<CallInst>(&I))
2568 if (CI->cannotDuplicate() || CI->isConvergent())
2569 return false;
2570
2571 // Ignore ephemeral values which are deleted during codegen.
2572 if (IsEphemeral(&I))
2573 EphValues.insert(&I);
2574 // We will delete Phis while threading, so Phis should not be accounted in
2575 // block's size.
2576 else if (!isa<PHINode>(I)) {
2577 if (Size++ > MaxSmallBlockSize)
2578 return false; // Don't clone large BB's.
2579 }
2580
2581 // We can only support instructions that do not define values that are
2582 // live outside of the current basic block.
2583 for (User *U : I.users()) {
2584 Instruction *UI = cast<Instruction>(U);
2585 if (UI->getParent() != BB || isa<PHINode>(UI))
2586 return false;
2587 }
2588
2589 // Looks ok, continue checking.
2590 }
2591
2592 return true;
2593}
2594
2595/// If we have a conditional branch on a PHI node value that is defined in the
2596/// same block as the branch and if any PHI entries are constants, thread edges
2597/// corresponding to that entry to be branches to their ultimate destination.
2598static bool FoldCondBranchOnPHI(BranchInst *BI, DomTreeUpdater *DTU,
2599 const DataLayout &DL, AssumptionCache *AC) {
2600 BasicBlock *BB = BI->getParent();
2601 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
2602 // NOTE: we currently cannot transform this case if the PHI node is used
2603 // outside of the block.
2604 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
2605 return false;
2606
2607 // Degenerate case of a single entry PHI.
2608 if (PN->getNumIncomingValues() == 1) {
2609 FoldSingleEntryPHINodes(PN->getParent());
2610 return true;
2611 }
2612
2613 // Now we know that this block has multiple preds and two succs.
2614 if (!BlockIsSimpleEnoughToThreadThrough(BB))
2615 return false;
2616
2617 // Okay, this is a simple enough basic block. See if any phi values are
2618 // constants.
2619 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2620 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
2621 if (!CB || !CB->getType()->isIntegerTy(1))
2622 continue;
2623
2624 // Okay, we now know that all edges from PredBB should be revectored to
2625 // branch to RealDest.
2626 BasicBlock *PredBB = PN->getIncomingBlock(i);
2627 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
2628
2629 if (RealDest == BB)
2630 continue; // Skip self loops.
2631 // Skip if the predecessor's terminator is an indirect branch.
2632 if (isa<IndirectBrInst>(PredBB->getTerminator()))
2633 continue;
2634
2635 SmallVector<DominatorTree::UpdateType, 3> Updates;
2636
2637 // The dest block might have PHI nodes, other predecessors and other
2638 // difficult cases. Instead of being smart about this, just insert a new
2639 // block that jumps to the destination block, effectively splitting
2640 // the edge we are about to create.
2641 BasicBlock *EdgeBB =
2642 BasicBlock::Create(BB->getContext(), RealDest->getName() + ".critedge",
2643 RealDest->getParent(), RealDest);
2644 BranchInst *CritEdgeBranch = BranchInst::Create(RealDest, EdgeBB);
2645 if (DTU)
2646 Updates.push_back({DominatorTree::Insert, EdgeBB, RealDest});
2647 CritEdgeBranch->setDebugLoc(BI->getDebugLoc());
2648
2649 // Update PHI nodes.
2650 AddPredecessorToBlock(RealDest, EdgeBB, BB);
2651
2652 // BB may have instructions that are being threaded over. Clone these
2653 // instructions into EdgeBB. We know that there will be no uses of the
2654 // cloned instructions outside of EdgeBB.
2655 BasicBlock::iterator InsertPt = EdgeBB->begin();
2656 DenseMap<Value *, Value *> TranslateMap; // Track translated values.
2657 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
2658 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
2659 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
2660 continue;
2661 }
2662 // Clone the instruction.
2663 Instruction *N = BBI->clone();
2664 if (BBI->hasName())
2665 N->setName(BBI->getName() + ".c");
2666
2667 // Update operands due to translation.
2668 for (Use &Op : N->operands()) {
2669 DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(Op);
2670 if (PI != TranslateMap.end())
2671 Op = PI->second;
2672 }
2673
2674 // Check for trivial simplification.
2675 if (Value *V = SimplifyInstruction(N, {DL, nullptr, nullptr, AC})) {
2676 if (!BBI->use_empty())
2677 TranslateMap[&*BBI] = V;
2678 if (!N->mayHaveSideEffects()) {
2679 N->deleteValue(); // Instruction folded away, don't need actual inst
2680 N = nullptr;
2681 }
2682 } else {
2683 if (!BBI->use_empty())
2684 TranslateMap[&*BBI] = N;
2685 }
2686 if (N) {
2687 // Insert the new instruction into its new home.
2688 EdgeBB->getInstList().insert(InsertPt, N);
2689
2690 // Register the new instruction with the assumption cache if necessary.
2691 if (auto *Assume = dyn_cast<AssumeInst>(N))
2692 if (AC)
2693 AC->registerAssumption(Assume);
2694 }
2695 }
2696
2697 // Loop over all of the edges from PredBB to BB, changing them to branch
2698 // to EdgeBB instead.
2699 Instruction *PredBBTI = PredBB->getTerminator();
2700 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
2701 if (PredBBTI->getSuccessor(i) == BB) {
2702 BB->removePredecessor(PredBB);
2703 PredBBTI->setSuccessor(i, EdgeBB);
2704 }
2705
2706 if (DTU) {
2707 Updates.push_back({DominatorTree::Insert, PredBB, EdgeBB});
2708 Updates.push_back({DominatorTree::Delete, PredBB, BB});
2709
2710 DTU->applyUpdates(Updates);
2711 }
2712
2713 // Recurse, simplifying any other constants.
2714 return FoldCondBranchOnPHI(BI, DTU, DL, AC) || true;
2715 }
2716
2717 return false;
2718}
2719
2720/// Given a BB that starts with the specified two-entry PHI node,
2721/// see if we can eliminate it.
2722static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
2723 DomTreeUpdater *DTU, const DataLayout &DL) {
2724 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
2725 // statement", which has a very simple dominance structure. Basically, we
2726 // are trying to find the condition that is being branched on, which
2727 // subsequently causes this merge to happen. We really want control
2728 // dependence information for this check, but simplifycfg can't keep it up
2729 // to date, and this catches most of the cases we care about anyway.
2730 BasicBlock *BB = PN->getParent();
2731
2732 BasicBlock *IfTrue, *IfFalse;
2733 BranchInst *DomBI = GetIfCondition(BB, IfTrue, IfFalse);
2734 if (!DomBI)
2735 return false;
2736 Value *IfCond = DomBI->getCondition();
2737 // Don't bother if the branch will be constant folded trivially.
2738 if (isa<ConstantInt>(IfCond))
2739 return false;
2740
2741 BasicBlock *DomBlock = DomBI->getParent();
2742 SmallVector<BasicBlock *, 2> IfBlocks;
2743 llvm::copy_if(
2744 PN->blocks(), std::back_inserter(IfBlocks), [](BasicBlock *IfBlock) {
2745 return cast<BranchInst>(IfBlock->getTerminator())->isUnconditional();
2746 });
2747 assert((IfBlocks.size() == 1 || IfBlocks.size() == 2) &&((void)0)
2748 "Will have either one or two blocks to speculate.")((void)0);
2749
2750 // If the branch is non-unpredictable, see if we either predictably jump to
2751 // the merge bb (if we have only a single 'then' block), or if we predictably
2752 // jump to one specific 'then' block (if we have two of them).
2753 // It isn't beneficial to speculatively execute the code
2754 // from the block that we know is predictably not entered.
2755 if (!DomBI->getMetadata(LLVMContext::MD_unpredictable)) {
2756 uint64_t TWeight, FWeight;
2757 if (DomBI->extractProfMetadata(TWeight, FWeight) &&
2758 (TWeight + FWeight) != 0) {
2759 BranchProbability BITrueProb =
2760 BranchProbability::getBranchProbability(TWeight, TWeight + FWeight);
2761 BranchProbability Likely = TTI.getPredictableBranchThreshold();
2762 BranchProbability BIFalseProb = BITrueProb.getCompl();
2763 if (IfBlocks.size() == 1) {
2764 BranchProbability BIBBProb =
2765 DomBI->getSuccessor(0) == BB ? BITrueProb : BIFalseProb;
2766 if (BIBBProb >= Likely)
2767 return false;
2768 } else {
2769 if (BITrueProb >= Likely || BIFalseProb >= Likely)
2770 return false;
2771 }
2772 }
2773 }
2774
2775 // Don't try to fold an unreachable block. For example, the phi node itself
2776 // can't be the candidate if-condition for a select that we want to form.
2777 if (auto *IfCondPhiInst = dyn_cast<PHINode>(IfCond))
2778 if (IfCondPhiInst->getParent() == BB)
2779 return false;
2780
2781 // Okay, we found that we can merge this two-entry phi node into a select.
2782 // Doing so would require us to fold *all* two entry phi nodes in this block.
2783 // At some point this becomes non-profitable (particularly if the target
2784 // doesn't support cmov's). Only do this transformation if there are two or
2785 // fewer PHI nodes in this block.
2786 unsigned NumPhis = 0;
2787 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
2788 if (NumPhis > 2)
2789 return false;
2790
2791 // Loop over the PHI's seeing if we can promote them all to select
2792 // instructions. While we are at it, keep track of the instructions
2793 // that need to be moved to the dominating block.
2794 SmallPtrSet<Instruction *, 4> AggressiveInsts;
2795 InstructionCost Cost = 0;
2796 InstructionCost Budget =
2797 TwoEntryPHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
2798
2799 bool Changed = false;
2800 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
2801 PHINode *PN = cast<PHINode>(II++);
2802 if (Value *V = SimplifyInstruction(PN, {DL, PN})) {
2803 PN->replaceAllUsesWith(V);
2804 PN->eraseFromParent();
2805 Changed = true;
2806 continue;
2807 }
2808
2809 if (!dominatesMergePoint(PN->getIncomingValue(0), BB, AggressiveInsts,
2810 Cost, Budget, TTI) ||
2811 !dominatesMergePoint(PN->getIncomingValue(1), BB, AggressiveInsts,
2812 Cost, Budget, TTI))
2813 return Changed;
2814 }
2815
2816 // If we folded the first phi, PN dangles at this point. Refresh it. If
2817 // we ran out of PHIs then we simplified them all.
2818 PN = dyn_cast<PHINode>(BB->begin());
2819 if (!PN)
2820 return true;
2821
2822 // Return true if at least one of these is a 'not', and another is either
2823 // a 'not' too, or a constant.
2824 auto CanHoistNotFromBothValues = [](Value *V0, Value *V1) {
2825 if (!match(V0, m_Not(m_Value())))
2826 std::swap(V0, V1);
2827 auto Invertible = m_CombineOr(m_Not(m_Value()), m_AnyIntegralConstant());
2828 return match(V0, m_Not(m_Value())) && match(V1, Invertible);
2829 };
2830
2831 // Don't fold i1 branches on PHIs which contain binary operators or
2832 // (possibly inverted) select form of or/ands, unless one of
2833 // the incoming values is an 'not' and another one is freely invertible.
2834 // These can often be turned into switches and other things.
2835 auto IsBinOpOrAnd = [](Value *V) {
2836 return match(
2837 V, m_CombineOr(
2838 m_BinOp(),
2839 m_CombineOr(m_Select(m_Value(), m_ImmConstant(), m_Value()),
2840 m_Select(m_Value(), m_Value(), m_ImmConstant()))));
2841 };
2842 if (PN->getType()->isIntegerTy(1) &&
2843 (IsBinOpOrAnd(PN->getIncomingValue(0)) ||
2844 IsBinOpOrAnd(PN->getIncomingValue(1)) || IsBinOpOrAnd(IfCond)) &&
2845 !CanHoistNotFromBothValues(PN->getIncomingValue(0),
2846 PN->getIncomingValue(1)))
2847 return Changed;
2848
2849 // If all PHI nodes are promotable, check to make sure that all instructions
2850 // in the predecessor blocks can be promoted as well. If not, we won't be able
2851 // to get rid of the control flow, so it's not worth promoting to select
2852 // instructions.
2853 for (BasicBlock *IfBlock : IfBlocks)
2854 for (BasicBlock::iterator I = IfBlock->begin(); !I->isTerminator(); ++I)
2855 if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I) &&
2856 !isa<PseudoProbeInst>(I)) {
2857 // This is not an aggressive instruction that we can promote.
2858 // Because of this, we won't be able to get rid of the control flow, so
2859 // the xform is not worth it.
2860 return Changed;
2861 }
2862
2863 // If either of the blocks has it's address taken, we can't do this fold.
2864 if (any_of(IfBlocks,
2865 [](BasicBlock *IfBlock) { return IfBlock->hasAddressTaken(); }))
2866 return Changed;
2867
2868 LLVM_DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfConddo { } while (false)
2869 << " T: " << IfTrue->getName()do { } while (false)
2870 << " F: " << IfFalse->getName() << "\n")do { } while (false);
2871
2872 // If we can still promote the PHI nodes after this gauntlet of tests,
2873 // do all of the PHI's now.
2874
2875 // Move all 'aggressive' instructions, which are defined in the
2876 // conditional parts of the if's up to the dominating block.
2877 for (BasicBlock *IfBlock : IfBlocks)
2878 hoistAllInstructionsInto(DomBlock, DomBI, IfBlock);
2879
2880 IRBuilder<NoFolder> Builder(DomBI);
2881 // Propagate fast-math-flags from phi nodes to replacement selects.
2882 IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
2883 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
2884 if (isa<FPMathOperator>(PN))
2885 Builder.setFastMathFlags(PN->getFastMathFlags());
2886
2887 // Change the PHI node into a select instruction.
2888 Value *TrueVal = PN->getIncomingValueForBlock(IfTrue);
2889 Value *FalseVal = PN->getIncomingValueForBlock(IfFalse);
2890
2891 Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
2892 PN->replaceAllUsesWith(Sel);
2893 Sel->takeName(PN);
2894 PN->eraseFromParent();
2895 }
2896
2897 // At this point, all IfBlocks are empty, so our if statement
2898 // has been flattened. Change DomBlock to jump directly to our new block to
2899 // avoid other simplifycfg's kicking in on the diamond.
2900 Builder.CreateBr(BB);
2901
2902 SmallVector<DominatorTree::UpdateType, 3> Updates;
2903 if (DTU) {
2904 Updates.push_back({DominatorTree::Insert, DomBlock, BB});
2905 for (auto *Successor : successors(DomBlock))
2906 Updates.push_back({DominatorTree::Delete, DomBlock, Successor});
2907 }
2908
2909 DomBI->eraseFromParent();
2910 if (DTU)
2911 DTU->applyUpdates(Updates);
2912
2913 return true;
2914}
2915
2916static Value *createLogicalOp(IRBuilderBase &Builder,
2917 Instruction::BinaryOps Opc, Value *LHS,
2918 Value *RHS, const Twine &Name = "") {
2919 // Try to relax logical op to binary op.
2920 if (impliesPoison(RHS, LHS))
2921 return Builder.CreateBinOp(Opc, LHS, RHS, Name);
2922 if (Opc == Instruction::And)
2923 return Builder.CreateLogicalAnd(LHS, RHS, Name);
2924 if (Opc == Instruction::Or)
2925 return Builder.CreateLogicalOr(LHS, RHS, Name);
2926 llvm_unreachable("Invalid logical opcode")__builtin_unreachable();
2927}
2928
2929/// Return true if either PBI or BI has branch weight available, and store
2930/// the weights in {Pred|Succ}{True|False}Weight. If one of PBI and BI does
2931/// not have branch weight, use 1:1 as its weight.
2932static bool extractPredSuccWeights(BranchInst *PBI, BranchInst *BI,
2933 uint64_t &PredTrueWeight,
2934 uint64_t &PredFalseWeight,
2935 uint64_t &SuccTrueWeight,
2936 uint64_t &SuccFalseWeight) {
2937 bool PredHasWeights =
2938 PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
2939 bool SuccHasWeights =
2940 BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
2941 if (PredHasWeights || SuccHasWeights) {
2942 if (!PredHasWeights)
2943 PredTrueWeight = PredFalseWeight = 1;
2944 if (!SuccHasWeights)
2945 SuccTrueWeight = SuccFalseWeight = 1;
2946 return true;
2947 } else {
2948 return false;
2949 }
2950}
2951
2952/// Determine if the two branches share a common destination and deduce a glue
2953/// that joins the branches' conditions to arrive at the common destination if
2954/// that would be profitable.
2955static Optional<std::pair<Instruction::BinaryOps, bool>>
2956shouldFoldCondBranchesToCommonDestination(BranchInst *BI, BranchInst *PBI,
2957 const TargetTransformInfo *TTI) {
2958 assert(BI && PBI && BI->isConditional() && PBI->isConditional() &&((void)0)
2959 "Both blocks must end with a conditional branches.")((void)0);
2960 assert(is_contained(predecessors(BI->getParent()), PBI->getParent()) &&((void)0)
2961 "PredBB must be a predecessor of BB.")((void)0);
2962
2963 // We have the potential to fold the conditions together, but if the
2964 // predecessor branch is predictable, we may not want to merge them.
2965 uint64_t PTWeight, PFWeight;
2966 BranchProbability PBITrueProb, Likely;
2967 if (TTI && !PBI->getMetadata(LLVMContext::MD_unpredictable) &&
2968 PBI->extractProfMetadata(PTWeight, PFWeight) &&
2969 (PTWeight + PFWeight) != 0) {
2970 PBITrueProb =
2971 BranchProbability::getBranchProbability(PTWeight, PTWeight + PFWeight);
2972 Likely = TTI->getPredictableBranchThreshold();
2973 }
2974
2975 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
2976 // Speculate the 2nd condition unless the 1st is probably true.
2977 if (PBITrueProb.isUnknown() || PBITrueProb < Likely)
2978 return {{Instruction::Or, false}};
2979 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
2980 // Speculate the 2nd condition unless the 1st is probably false.
2981 if (PBITrueProb.isUnknown() || PBITrueProb.getCompl() < Likely)
2982 return {{Instruction::And, false}};
2983 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
2984 // Speculate the 2nd condition unless the 1st is probably true.
2985 if (PBITrueProb.isUnknown() || PBITrueProb < Likely)
2986 return {{Instruction::And, true}};
2987 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
2988 // Speculate the 2nd condition unless the 1st is probably false.
2989 if (PBITrueProb.isUnknown() || PBITrueProb.getCompl() < Likely)
2990 return {{Instruction::Or, true}};
2991 }
2992 return None;
2993}
2994
2995static bool performBranchToCommonDestFolding(BranchInst *BI, BranchInst *PBI,
2996 DomTreeUpdater *DTU,
2997 MemorySSAUpdater *MSSAU,
2998 const TargetTransformInfo *TTI) {
2999 BasicBlock *BB = BI->getParent();
3000 BasicBlock *PredBlock = PBI->getParent();
3001
3002 // Determine if the two branches share a common destination.
3003 Instruction::BinaryOps Opc;
3004 bool InvertPredCond;
3005 std::tie(Opc, InvertPredCond) =
3006 *shouldFoldCondBranchesToCommonDestination(BI, PBI, TTI);
3007
3008 LLVM_DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB)do { } while (false);
3009
3010 IRBuilder<> Builder(PBI);
3011 // The builder is used to create instructions to eliminate the branch in BB.
3012 // If BB's terminator has !annotation metadata, add it to the new
3013 // instructions.
3014 Builder.CollectMetadataToCopy(BB->getTerminator(),
3015 {LLVMContext::MD_annotation});
3016
3017 // If we need to invert the condition in the pred block to match, do so now.
3018 if (InvertPredCond) {
3019 Value *NewCond = PBI->getCondition();
3020 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
3021 CmpInst *CI = cast<CmpInst>(NewCond);
3022 CI->setPredicate(CI->getInversePredicate());
3023 } else {
3024 NewCond =
3025 Builder.CreateNot(NewCond, PBI->getCondition()->getName() + ".not");
3026 }
3027
3028 PBI->setCondition(NewCond);
3029 PBI->swapSuccessors();
3030 }
3031
3032 BasicBlock *UniqueSucc =
3033 PBI->getSuccessor(0) == BB ? BI->getSuccessor(0) : BI->getSuccessor(1);
3034
3035 // Before cloning instructions, notify the successor basic block that it
3036 // is about to have a new predecessor. This will update PHI nodes,
3037 // which will allow us to update live-out uses of bonus instructions.
3038 AddPredecessorToBlock(UniqueSucc, PredBlock, BB, MSSAU);
3039
3040 // Try to update branch weights.
3041 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
3042 if (extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
3043 SuccTrueWeight, SuccFalseWeight)) {
3044 SmallVector<uint64_t, 8> NewWeights;
3045
3046 if (PBI->getSuccessor(0) == BB) {
3047 // PBI: br i1 %x, BB, FalseDest
3048 // BI: br i1 %y, UniqueSucc, FalseDest
3049 // TrueWeight is TrueWeight for PBI * TrueWeight for BI.
3050 NewWeights.push_back(PredTrueWeight * SuccTrueWeight);
3051 // FalseWeight is FalseWeight for PBI * TotalWeight for BI +
3052 // TrueWeight for PBI * FalseWeight for BI.
3053 // We assume that total weights of a BranchInst can fit into 32 bits.
3054 // Therefore, we will not have overflow using 64-bit arithmetic.
3055 NewWeights.push_back(PredFalseWeight *
3056 (SuccFalseWeight + SuccTrueWeight) +
3057 PredTrueWeight * SuccFalseWeight);
3058 } else {
3059 // PBI: br i1 %x, TrueDest, BB
3060 // BI: br i1 %y, TrueDest, UniqueSucc
3061 // TrueWeight is TrueWeight for PBI * TotalWeight for BI +
3062 // FalseWeight for PBI * TrueWeight for BI.
3063 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight + SuccTrueWeight) +
3064 PredFalseWeight * SuccTrueWeight);
3065 // FalseWeight is FalseWeight for PBI * FalseWeight for BI.
3066 NewWeights.push_back(PredFalseWeight * SuccFalseWeight);
3067 }
3068
3069 // Halve the weights if any of them cannot fit in an uint32_t
3070 FitWeights(NewWeights);
3071
3072 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(), NewWeights.end());
3073 setBranchWeights(PBI, MDWeights[0], MDWeights[1]);
3074
3075 // TODO: If BB is reachable from all paths through PredBlock, then we
3076 // could replace PBI's branch probabilities with BI's.
3077 } else
3078 PBI->setMetadata(LLVMContext::MD_prof, nullptr);
3079
3080 // Now, update the CFG.
3081 PBI->setSuccessor(PBI->getSuccessor(0) != BB, UniqueSucc);
3082
3083 if (DTU)
3084 DTU->applyUpdates({{DominatorTree::Insert, PredBlock, UniqueSucc},
3085 {DominatorTree::Delete, PredBlock, BB}});
3086
3087 // If BI was a loop latch, it may have had associated loop metadata.
3088 // We need to copy it to the new latch, that is, PBI.
3089 if (MDNode *LoopMD = BI->getMetadata(LLVMContext::MD_loop))
3090 PBI->setMetadata(LLVMContext::MD_loop, LoopMD);
3091
3092 ValueToValueMapTy VMap; // maps original values to cloned values
3093 CloneInstructionsIntoPredecessorBlockAndUpdateSSAUses(BB, PredBlock, VMap);
3094
3095 // Now that the Cond was cloned into the predecessor basic block,
3096 // or/and the two conditions together.
3097 Value *BICond = VMap[BI->getCondition()];
3098 PBI->setCondition(
3099 createLogicalOp(Builder, Opc, PBI->getCondition(), BICond, "or.cond"));
3100
3101 // Copy any debug value intrinsics into the end of PredBlock.
3102 for (Instruction &I : *BB) {
3103 if (isa<DbgInfoIntrinsic>(I)) {
3104 Instruction *NewI = I.clone();
3105 RemapInstruction(NewI, VMap,
3106 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
3107 NewI->insertBefore(PBI);
3108 }
3109 }
3110
3111 ++NumFoldBranchToCommonDest;
3112 return true;
3113}
3114
3115/// If this basic block is simple enough, and if a predecessor branches to us
3116/// and one of our successors, fold the block into the predecessor and use
3117/// logical operations to pick the right destination.
3118bool llvm::FoldBranchToCommonDest(BranchInst *BI, DomTreeUpdater *DTU,
3119 MemorySSAUpdater *MSSAU,
3120 const TargetTransformInfo *TTI,
3121 unsigned BonusInstThreshold) {
3122 // If this block ends with an unconditional branch,
3123 // let SpeculativelyExecuteBB() deal with it.
3124 if (!BI->isConditional())
3125 return false;
3126
3127 BasicBlock *BB = BI->getParent();
3128 TargetTransformInfo::TargetCostKind CostKind =
3129 BB->getParent()->hasMinSize() ? TargetTransformInfo::TCK_CodeSize
3130 : TargetTransformInfo::TCK_SizeAndLatency;
3131
3132 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
3133
3134 if (!Cond || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
3135 Cond->getParent() != BB || !Cond->hasOneUse())
3136 return false;
3137
3138 // Cond is known to be a compare or binary operator. Check to make sure that
3139 // neither operand is a potentially-trapping constant expression.
3140 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
3141 if (CE->canTrap())
3142 return false;
3143 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
3144 if (CE->canTrap())
3145 return false;
3146
3147 // Finally, don't infinitely unroll conditional loops.
3148 if (is_contained(successors(BB), BB))
3149 return false;
3150
3151 // With which predecessors will we want to deal with?
3152 SmallVector<BasicBlock *, 8> Preds;
3153 for (BasicBlock *PredBlock : predecessors(BB)) {
3154 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
3155
3156 // Check that we have two conditional branches. If there is a PHI node in
3157 // the common successor, verify that the same value flows in from both
3158 // blocks.
3159 if (!PBI || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
3160 continue;
3161
3162 // Determine if the two branches share a common destination.
3163 Instruction::BinaryOps Opc;
3164 bool InvertPredCond;
3165 if (auto Recipe = shouldFoldCondBranchesToCommonDestination(BI, PBI, TTI))
3166 std::tie(Opc, InvertPredCond) = *Recipe;
3167 else
3168 continue;
3169
3170 // Check the cost of inserting the necessary logic before performing the
3171 // transformation.
3172 if (TTI) {
3173 Type *Ty = BI->getCondition()->getType();
3174 InstructionCost Cost = TTI->getArithmeticInstrCost(Opc, Ty, CostKind);
3175 if (InvertPredCond && (!PBI->getCondition()->hasOneUse() ||
3176 !isa<CmpInst>(PBI->getCondition())))
3177 Cost += TTI->getArithmeticInstrCost(Instruction::Xor, Ty, CostKind);
3178
3179 if (Cost > BranchFoldThreshold)
3180 continue;
3181 }
3182
3183 // Ok, we do want to deal with this predecessor. Record it.
3184 Preds.emplace_back(PredBlock);
3185 }
3186
3187 // If there aren't any predecessors into which we can fold,
3188 // don't bother checking the cost.
3189 if (Preds.empty())
3190 return false;
3191
3192 // Only allow this transformation if computing the condition doesn't involve
3193 // too many instructions and these involved instructions can be executed
3194 // unconditionally. We denote all involved instructions except the condition
3195 // as "bonus instructions", and only allow this transformation when the
3196 // number of the bonus instructions we'll need to create when cloning into
3197 // each predecessor does not exceed a certain threshold.
3198 unsigned NumBonusInsts = 0;
3199 const unsigned PredCount = Preds.size();
3200 for (Instruction &I : *BB) {
3201 // Don't check the branch condition comparison itself.
3202 if (&I == Cond)
3203 continue;
3204 // Ignore dbg intrinsics, and the terminator.
3205 if (isa<DbgInfoIntrinsic>(I) || isa<BranchInst>(I))
3206 continue;
3207 // I must be safe to execute unconditionally.
3208 if (!isSafeToSpeculativelyExecute(&I))
3209 return false;
3210
3211 // Account for the cost of duplicating this instruction into each
3212 // predecessor.
3213 NumBonusInsts += PredCount;
3214 // Early exits once we reach the limit.
3215 if (NumBonusInsts > BonusInstThreshold)
3216 return false;
3217
3218 auto IsBCSSAUse = [BB, &I](Use &U) {
3219 auto *UI = cast<Instruction>(U.getUser());
3220 if (auto *PN = dyn_cast<PHINode>(UI))
3221 return PN->getIncomingBlock(U) == BB;
3222 return UI->getParent() == BB && I.comesBefore(UI);
3223 };
3224
3225 // Does this instruction require rewriting of uses?
3226 if (!all_of(I.uses(), IsBCSSAUse))
3227 return false;
3228 }
3229
3230 // Ok, we have the budget. Perform the transformation.
3231 for (BasicBlock *PredBlock : Preds) {
3232 auto *PBI = cast<BranchInst>(PredBlock->getTerminator());
3233 return performBranchToCommonDestFolding(BI, PBI, DTU, MSSAU, TTI);
3234 }
3235 return false;
3236}
3237
3238// If there is only one store in BB1 and BB2, return it, otherwise return
3239// nullptr.
3240static StoreInst *findUniqueStoreInBlocks(BasicBlock *BB1, BasicBlock *BB2) {
3241 StoreInst *S = nullptr;
3242 for (auto *BB : {BB1, BB2}) {
3243 if (!BB)
3244 continue;
3245 for (auto &I : *BB)
3246 if (auto *SI = dyn_cast<StoreInst>(&I)) {
3247 if (S)
3248 // Multiple stores seen.
3249 return nullptr;
3250 else
3251 S = SI;
3252 }
3253 }
3254 return S;
3255}
3256
3257static Value *ensureValueAvailableInSuccessor(Value *V, BasicBlock *BB,
3258 Value *AlternativeV = nullptr) {
3259 // PHI is going to be a PHI node that allows the value V that is defined in
3260 // BB to be referenced in BB's only successor.
3261 //
3262 // If AlternativeV is nullptr, the only value we care about in PHI is V. It
3263 // doesn't matter to us what the other operand is (it'll never get used). We
3264 // could just create a new PHI with an undef incoming value, but that could
3265 // increase register pressure if EarlyCSE/InstCombine can't fold it with some
3266 // other PHI. So here we directly look for some PHI in BB's successor with V
3267 // as an incoming operand. If we find one, we use it, else we create a new
3268 // one.
3269 //
3270 // If AlternativeV is not nullptr, we care about both incoming values in PHI.
3271 // PHI must be exactly: phi <ty> [ %BB, %V ], [ %OtherBB, %AlternativeV]
3272 // where OtherBB is the single other predecessor of BB's only successor.
3273 PHINode *PHI = nullptr;
3274 BasicBlock *Succ = BB->getSingleSuccessor();
3275
3276 for (auto I = Succ->begin(); isa<PHINode>(I); ++I)
3277 if (cast<PHINode>(I)->getIncomingValueForBlock(BB) == V) {
3278 PHI = cast<PHINode>(I);
3279 if (!AlternativeV)
3280 break;
3281
3282 assert(Succ->hasNPredecessors(2))((void)0);
3283 auto PredI = pred_begin(Succ);
3284 BasicBlock *OtherPredBB = *PredI == BB ? *++PredI : *PredI;
3285 if (PHI->getIncomingValueForBlock(OtherPredBB) == AlternativeV)
3286 break;
3287 PHI = nullptr;
3288 }
3289 if (PHI)
3290 return PHI;
3291
3292 // If V is not an instruction defined in BB, just return it.
3293 if (!AlternativeV &&
3294 (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB))
3295 return V;
3296
3297 PHI = PHINode::Create(V->getType(), 2, "simplifycfg.merge", &Succ->front());
3298 PHI->addIncoming(V, BB);
3299 for (BasicBlock *PredBB : predecessors(Succ))
3300 if (PredBB != BB)
3301 PHI->addIncoming(
3302 AlternativeV ? AlternativeV : UndefValue::get(V->getType()), PredBB);
3303 return PHI;
3304}
3305
3306static bool mergeConditionalStoreToAddress(
3307 BasicBlock *PTB, BasicBlock *PFB, BasicBlock *QTB, BasicBlock *QFB,
3308 BasicBlock *PostBB, Value *Address, bool InvertPCond, bool InvertQCond,
3309 DomTreeUpdater *DTU, const DataLayout &DL, const TargetTransformInfo &TTI) {
3310 // For every pointer, there must be exactly two stores, one coming from
3311 // PTB or PFB, and the other from QTB or QFB. We don't support more than one
3312 // store (to any address) in PTB,PFB or QTB,QFB.
3313 // FIXME: We could relax this restriction with a bit more work and performance
3314 // testing.
3315 StoreInst *PStore = findUniqueStoreInBlocks(PTB, PFB);
3316 StoreInst *QStore = findUniqueStoreInBlocks(QTB, QFB);
3317 if (!PStore || !QStore)
3318 return false;
3319
3320 // Now check the stores are compatible.
3321 if (!QStore->isUnordered() || !PStore->isUnordered())
3322 return false;
3323
3324 // Check that sinking the store won't cause program behavior changes. Sinking
3325 // the store out of the Q blocks won't change any behavior as we're sinking
3326 // from a block to its unconditional successor. But we're moving a store from
3327 // the P blocks down through the middle block (QBI) and past both QFB and QTB.
3328 // So we need to check that there are no aliasing loads or stores in
3329 // QBI, QTB and QFB. We also need to check there are no conflicting memory
3330 // operations between PStore and the end of its parent block.
3331 //
3332 // The ideal way to do this is to query AliasAnalysis, but we don't
3333 // preserve AA currently so that is dangerous. Be super safe and just
3334 // check there are no other memory operations at all.
3335 for (auto &I : *QFB->getSinglePredecessor())
3336 if (I.mayReadOrWriteMemory())
3337 return false;
3338 for (auto &I : *QFB)
3339 if (&I != QStore && I.mayReadOrWriteMemory())
3340 return false;
3341 if (QTB)
3342 for (auto &I : *QTB)
3343 if (&I != QStore && I.mayReadOrWriteMemory())
3344 return false;
3345 for (auto I = BasicBlock::iterator(PStore), E = PStore->getParent()->end();
3346 I != E; ++I)
3347 if (&*I != PStore && I->mayReadOrWriteMemory())
3348 return false;
3349
3350 // If we're not in aggressive mode, we only optimize if we have some
3351 // confidence that by optimizing we'll allow P and/or Q to be if-converted.
3352 auto IsWorthwhile = [&](BasicBlock *BB, ArrayRef<StoreInst *> FreeStores) {
3353 if (!BB)
3354 return true;
3355 // Heuristic: if the block can be if-converted/phi-folded and the
3356 // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
3357 // thread this store.
3358 InstructionCost Cost = 0;
3359 InstructionCost Budget =
3360 PHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
3361 for (auto &I : BB->instructionsWithoutDebug()) {
3362 // Consider terminator instruction to be free.
3363 if (I.isTerminator())
3364 continue;
3365 // If this is one the stores that we want to speculate out of this BB,
3366 // then don't count it's cost, consider it to be free.
3367 if (auto *S = dyn_cast<StoreInst>(&I))
3368 if (llvm::find(FreeStores, S))
3369 continue;
3370 // Else, we have a white-list of instructions that we are ak speculating.
3371 if (!isa<BinaryOperator>(I) && !isa<GetElementPtrInst>(I))
3372 return false; // Not in white-list - not worthwhile folding.
3373 // And finally, if this is a non-free instruction that we are okay
3374 // speculating, ensure that we consider the speculation budget.
3375 Cost += TTI.getUserCost(&I, TargetTransformInfo::TCK_SizeAndLatency);
3376 if (Cost > Budget)
3377 return false; // Eagerly refuse to fold as soon as we're out of budget.
3378 }
3379 assert(Cost <= Budget &&((void)0)
3380 "When we run out of budget we will eagerly return from within the "((void)0)
3381 "per-instruction loop.")((void)0);
3382 return true;
3383 };
3384
3385 const std::array<StoreInst *, 2> FreeStores = {PStore, QStore};
3386 if (!MergeCondStoresAggressively &&
3387 (!IsWorthwhile(PTB, FreeStores) || !IsWorthwhile(PFB, FreeStores) ||
3388 !IsWorthwhile(QTB, FreeStores) || !IsWorthwhile(QFB, FreeStores)))
3389 return false;
3390
3391 // If PostBB has more than two predecessors, we need to split it so we can
3392 // sink the store.
3393 if (std::next(pred_begin(PostBB), 2) != pred_end(PostBB)) {
3394 // We know that QFB's only successor is PostBB. And QFB has a single
3395 // predecessor. If QTB exists, then its only successor is also PostBB.
3396 // If QTB does not exist, then QFB's only predecessor has a conditional
3397 // branch to QFB and PostBB.
3398 BasicBlock *TruePred = QTB ? QTB : QFB->getSinglePredecessor();
3399 BasicBlock *NewBB =
3400 SplitBlockPredecessors(PostBB, {QFB, TruePred}, "condstore.split", DTU);
3401 if (!NewBB)
3402 return false;
3403 PostBB = NewBB;
3404 }
3405
3406 // OK, we're going to sink the stores to PostBB. The store has to be
3407 // conditional though, so first create the predicate.
3408 Value *PCond = cast<BranchInst>(PFB->getSinglePredecessor()->getTerminator())
3409 ->getCondition();
3410 Value *QCond = cast<BranchInst>(QFB->getSinglePredecessor()->getTerminator())
3411 ->getCondition();
3412
3413 Value *PPHI = ensureValueAvailableInSuccessor(PStore->getValueOperand(),
3414 PStore->getParent());
3415 Value *QPHI = ensureValueAvailableInSuccessor(QStore->getValueOperand(),
3416 QStore->getParent(), PPHI);
3417
3418 IRBuilder<> QB(&*PostBB->getFirstInsertionPt());
3419
3420 Value *PPred = PStore->getParent() == PTB ? PCond : QB.CreateNot(PCond);
3421 Value *QPred = QStore->getParent() == QTB ? QCond : QB.CreateNot(QCond);
3422
3423 if (InvertPCond)
3424 PPred = QB.CreateNot(PPred);
3425 if (InvertQCond)
3426 QPred = QB.CreateNot(QPred);
3427 Value *CombinedPred = QB.CreateOr(PPred, QPred);
3428
3429 auto *T = SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(),
3430 /*Unreachable=*/false,
3431 /*BranchWeights=*/nullptr, DTU);
3432 QB.SetInsertPoint(T);
3433 StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
3434 AAMDNodes AAMD;
3435 PStore->getAAMetadata(AAMD, /*Merge=*/false);
3436 PStore->getAAMetadata(AAMD, /*Merge=*/true);
3437 SI->setAAMetadata(AAMD);
3438 // Choose the minimum alignment. If we could prove both stores execute, we
3439 // could use biggest one. In this case, though, we only know that one of the
3440 // stores executes. And we don't know it's safe to take the alignment from a
3441 // store that doesn't execute.
3442 SI->setAlignment(std::min(PStore->getAlign(), QStore->getAlign()));
3443
3444 QStore->eraseFromParent();
3445 PStore->eraseFromParent();
3446
3447 return true;
3448}
3449
3450static bool mergeConditionalStores(BranchInst *PBI, BranchInst *QBI,
3451 DomTreeUpdater *DTU, const DataLayout &DL,
3452 const TargetTransformInfo &TTI) {
3453 // The intention here is to find diamonds or triangles (see below) where each
3454 // conditional block contains a store to the same address. Both of these
3455 // stores are conditional, so they can't be unconditionally sunk. But it may
3456 // be profitable to speculatively sink the stores into one merged store at the
3457 // end, and predicate the merged store on the union of the two conditions of
3458 // PBI and QBI.
3459 //
3460 // This can reduce the number of stores executed if both of the conditions are
3461 // true, and can allow the blocks to become small enough to be if-converted.
3462 // This optimization will also chain, so that ladders of test-and-set
3463 // sequences can be if-converted away.
3464 //
3465 // We only deal with simple diamonds or triangles:
3466 //
3467 // PBI or PBI or a combination of the two
3468 // / \ | \
3469 // PTB PFB | PFB
3470 // \ / | /
3471 // QBI QBI
3472 // / \ | \
3473 // QTB QFB | QFB
3474 // \ / | /
3475 // PostBB PostBB
3476 //
3477 // We model triangles as a type of diamond with a nullptr "true" block.
3478 // Triangles are canonicalized so that the fallthrough edge is represented by
3479 // a true condition, as in the diagram above.
3480 BasicBlock *PTB = PBI->getSuccessor(0);
3481 BasicBlock *PFB = PBI->getSuccessor(1);
3482 BasicBlock *QTB = QBI->getSuccessor(0);
3483 BasicBlock *QFB = QBI->getSuccessor(1);
3484 BasicBlock *PostBB = QFB->getSingleSuccessor();
3485
3486 // Make sure we have a good guess for PostBB. If QTB's only successor is
3487 // QFB, then QFB is a better PostBB.
3488 if (QTB->getSingleSuccessor() == QFB)
3489 PostBB = QFB;
3490
3491 // If we couldn't find a good PostBB, stop.
3492 if (!PostBB)
3493 return false;
3494
3495 bool InvertPCond = false, InvertQCond = false;
3496 // Canonicalize fallthroughs to the true branches.
3497 if (PFB == QBI->getParent()) {
3498 std::swap(PFB, PTB);
3499 InvertPCond = true;
3500 }
3501 if (QFB == PostBB) {
3502 std::swap(QFB, QTB);
3503 InvertQCond = true;
3504 }
3505
3506 // From this point on we can assume PTB or QTB may be fallthroughs but PFB
3507 // and QFB may not. Model fallthroughs as a nullptr block.
3508 if (PTB == QBI->getParent())
3509 PTB = nullptr;
3510 if (QTB == PostBB)
3511 QTB = nullptr;
3512
3513 // Legality bailouts. We must have at least the non-fallthrough blocks and
3514 // the post-dominating block, and the non-fallthroughs must only have one
3515 // predecessor.
3516 auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
3517 return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S;
3518 };
3519 if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
3520 !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
3521 return false;
3522 if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||
3523 (QTB && !HasOnePredAndOneSucc(QTB, QBI->getParent(), PostBB)))
3524 return false;
3525 if (!QBI->getParent()->hasNUses(2))
3526 return false;
3527
3528 // OK, this is a sequence of two diamonds or triangles.
3529 // Check if there are stores in PTB or PFB that are repeated in QTB or QFB.
3530 SmallPtrSet<Value *, 4> PStoreAddresses, QStoreAddresses;
3531 for (auto *BB : {PTB, PFB}) {
3532 if (!BB)
3533 continue;
3534 for (auto &I : *BB)
3535 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3536 PStoreAddresses.insert(SI->getPointerOperand());
3537 }
3538 for (auto *BB : {QTB, QFB}) {
3539 if (!BB)
3540 continue;
3541 for (auto &I : *BB)
3542 if (StoreInst *SI = dyn_cast<StoreInst>(&I))
3543 QStoreAddresses.insert(SI->getPointerOperand());
3544 }
3545
3546 set_intersect(PStoreAddresses, QStoreAddresses);
3547 // set_intersect mutates PStoreAddresses in place. Rename it here to make it
3548 // clear what it contains.
3549 auto &CommonAddresses = PStoreAddresses;
3550
3551 bool Changed = false;
3552 for (auto *Address : CommonAddresses)
3553 Changed |=
3554 mergeConditionalStoreToAddress(PTB, PFB, QTB, QFB, PostBB, Address,
3555 InvertPCond, InvertQCond, DTU, DL, TTI);
3556 return Changed;
3557}
3558
3559/// If the previous block ended with a widenable branch, determine if reusing
3560/// the target block is profitable and legal. This will have the effect of
3561/// "widening" PBI, but doesn't require us to reason about hosting safety.
3562static bool tryWidenCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
3563 DomTreeUpdater *DTU) {
3564 // TODO: This can be generalized in two important ways:
3565 // 1) We can allow phi nodes in IfFalseBB and simply reuse all the input
3566 // values from the PBI edge.
3567 // 2) We can sink side effecting instructions into BI's fallthrough
3568 // successor provided they doesn't contribute to computation of
3569 // BI's condition.
3570 Value *CondWB, *WC;
3571 BasicBlock *IfTrueBB, *IfFalseBB;
3572 if (!parseWidenableBranch(PBI, CondWB, WC, IfTrueBB, IfFalseBB) ||
3573 IfTrueBB != BI->getParent() || !BI->getParent()->getSinglePredecessor())
3574 return false;
3575 if (!IfFalseBB->phis().empty())
3576 return false; // TODO
3577 // Use lambda to lazily compute expensive condition after cheap ones.
3578 auto NoSideEffects = [](BasicBlock &BB) {
3579 return !llvm::any_of(BB, [](const Instruction &I) {
3580 return I.mayWriteToMemory() || I.mayHaveSideEffects();
3581 });
3582 };
3583 if (BI->getSuccessor(1) != IfFalseBB && // no inf looping
3584 BI->getSuccessor(1)->getTerminatingDeoptimizeCall() && // profitability
3585 NoSideEffects(*BI->getParent())) {
3586 auto *OldSuccessor = BI->getSuccessor(1);
3587 OldSuccessor->removePredecessor(BI->getParent());
3588 BI->setSuccessor(1, IfFalseBB);
3589 if (DTU)
3590 DTU->applyUpdates(
3591 {{DominatorTree::Insert, BI->getParent(), IfFalseBB},
3592 {DominatorTree::Delete, BI->getParent(), OldSuccessor}});
3593 return true;
3594 }
3595 if (BI->getSuccessor(0) != IfFalseBB && // no inf looping
3596 BI->getSuccessor(0)->getTerminatingDeoptimizeCall() && // profitability
3597 NoSideEffects(*BI->getParent())) {
3598 auto *OldSuccessor = BI->getSuccessor(0);
3599 OldSuccessor->removePredecessor(BI->getParent());
3600 BI->setSuccessor(0, IfFalseBB);
3601 if (DTU)
3602 DTU->applyUpdates(
3603 {{DominatorTree::Insert, BI->getParent(), IfFalseBB},
3604 {DominatorTree::Delete, BI->getParent(), OldSuccessor}});
3605 return true;
3606 }
3607 return false;
3608}
3609
3610/// If we have a conditional branch as a predecessor of another block,
3611/// this function tries to simplify it. We know
3612/// that PBI and BI are both conditional branches, and BI is in one of the
3613/// successor blocks of PBI - PBI branches to BI.
3614static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
3615 DomTreeUpdater *DTU,
3616 const DataLayout &DL,
3617 const TargetTransformInfo &TTI) {
3618 assert(PBI->isConditional() && BI->isConditional())((void)0);
3619 BasicBlock *BB = BI->getParent();
3620
3621 // If this block ends with a branch instruction, and if there is a
3622 // predecessor that ends on a branch of the same condition, make
3623 // this conditional branch redundant.
3624 if (PBI->getCondition() == BI->getCondition() &&
3625 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3626 // Okay, the outcome of this conditional branch is statically
3627 // knowable. If this block had a single pred, handle specially.
3628 if (BB->getSinglePredecessor()) {
3629 // Turn this into a branch on constant.
3630 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3631 BI->setCondition(
3632 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue));
3633 return true; // Nuke the branch on constant.
3634 }
3635
3636 // Otherwise, if there are multiple predecessors, insert a PHI that merges
3637 // in the constant and simplify the block result. Subsequent passes of
3638 // simplifycfg will thread the block.
3639 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
3640 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
3641 PHINode *NewPN = PHINode::Create(
3642 Type::getInt1Ty(BB->getContext()), std::distance(PB, PE),
3643 BI->getCondition()->getName() + ".pr", &BB->front());
3644 // Okay, we're going to insert the PHI node. Since PBI is not the only
3645 // predecessor, compute the PHI'd conditional value for all of the preds.
3646 // Any predecessor where the condition is not computable we keep symbolic.
3647 for (pred_iterator PI = PB; PI != PE; ++PI) {
3648 BasicBlock *P = *PI;
3649 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && PBI != BI &&
3650 PBI->isConditional() && PBI->getCondition() == BI->getCondition() &&
3651 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
3652 bool CondIsTrue = PBI->getSuccessor(0) == BB;
3653 NewPN->addIncoming(
3654 ConstantInt::get(Type::getInt1Ty(BB->getContext()), CondIsTrue),
3655 P);
3656 } else {
3657 NewPN->addIncoming(BI->getCondition(), P);
3658 }
3659 }
3660
3661 BI->setCondition(NewPN);
3662 return true;
3663 }
3664 }
3665
3666 // If the previous block ended with a widenable branch, determine if reusing
3667 // the target block is profitable and legal. This will have the effect of
3668 // "widening" PBI, but doesn't require us to reason about hosting safety.
3669 if (tryWidenCondBranchToCondBranch(PBI, BI, DTU))
3670 return true;
3671
3672 if (auto *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
3673 if (CE->canTrap())
3674 return false;
3675
3676 // If both branches are conditional and both contain stores to the same
3677 // address, remove the stores from the conditionals and create a conditional
3678 // merged store at the end.
3679 if (MergeCondStores && mergeConditionalStores(PBI, BI, DTU, DL, TTI))
3680 return true;
3681
3682 // If this is a conditional branch in an empty block, and if any
3683 // predecessors are a conditional branch to one of our destinations,
3684 // fold the conditions into logical ops and one cond br.
3685
3686 // Ignore dbg intrinsics.
3687 if (&*BB->instructionsWithoutDebug().begin() != BI)
3688 return false;
3689
3690 int PBIOp, BIOp;
3691 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
3692 PBIOp = 0;
3693 BIOp = 0;
3694 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
3695 PBIOp = 0;
3696 BIOp = 1;
3697 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
3698 PBIOp = 1;
3699 BIOp = 0;
3700 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
3701 PBIOp = 1;
3702 BIOp = 1;
3703 } else {
3704 return false;
3705 }
3706
3707 // Check to make sure that the other destination of this branch
3708 // isn't BB itself. If so, this is an infinite loop that will
3709 // keep getting unwound.
3710 if (PBI->getSuccessor(PBIOp) == BB)
3711 return false;
3712
3713 // Do not perform this transformation if it would require
3714 // insertion of a large number of select instructions. For targets
3715 // without predication/cmovs, this is a big pessimization.
3716
3717 // Also do not perform this transformation if any phi node in the common
3718 // destination block can trap when reached by BB or PBB (PR17073). In that
3719 // case, it would be unsafe to hoist the operation into a select instruction.
3720
3721 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
3722 BasicBlock *RemovedDest = PBI->getSuccessor(PBIOp ^ 1);
3723 unsigned NumPhis = 0;
3724 for (BasicBlock::iterator II = CommonDest->begin(); isa<PHINode>(II);
3725 ++II, ++NumPhis) {
3726 if (NumPhis > 2) // Disable this xform.
3727 return false;
3728
3729 PHINode *PN = cast<PHINode>(II);
3730 Value *BIV = PN->getIncomingValueForBlock(BB);
3731 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BIV))
3732 if (CE->canTrap())
3733 return false;
3734
3735 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
3736 Value *PBIV = PN->getIncomingValue(PBBIdx);
3737 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(PBIV))
3738 if (CE->canTrap())
3739 return false;
3740 }
3741
3742 // Finally, if everything is ok, fold the branches to logical ops.
3743 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
3744
3745 LLVM_DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()do { } while (false)
3746 << "AND: " << *BI->getParent())do { } while (false);
3747
3748 SmallVector<DominatorTree::UpdateType, 5> Updates;
3749
3750 // If OtherDest *is* BB, then BB is a basic block with a single conditional
3751 // branch in it, where one edge (OtherDest) goes back to itself but the other
3752 // exits. We don't *know* that the program avoids the infinite loop
3753 // (even though that seems likely). If we do this xform naively, we'll end up
3754 // recursively unpeeling the loop. Since we know that (after the xform is
3755 // done) that the block *is* infinite if reached, we just make it an obviously
3756 // infinite loop with no cond branch.
3757 if (OtherDest == BB) {
3758 // Insert it at the end of the function, because it's either code,
3759 // or it won't matter if it's hot. :)
3760 BasicBlock *InfLoopBlock =
3761 BasicBlock::Create(BB->getContext(), "infloop", BB->getParent());
3762 BranchInst::Create(InfLoopBlock, InfLoopBlock);
3763 if (DTU)
3764 Updates.push_back({DominatorTree::Insert, InfLoopBlock, InfLoopBlock});
3765 OtherDest = InfLoopBlock;
3766 }
3767
3768 LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent())do { } while (false);
3769
3770 // BI may have other predecessors. Because of this, we leave
3771 // it alone, but modify PBI.
3772
3773 // Make sure we get to CommonDest on True&True directions.
3774 Value *PBICond = PBI->getCondition();
3775 IRBuilder<NoFolder> Builder(PBI);
3776 if (PBIOp)
3777 PBICond = Builder.CreateNot(PBICond, PBICond->getName() + ".not");
3778
3779 Value *BICond = BI->getCondition();
3780 if (BIOp)
3781 BICond = Builder.CreateNot(BICond, BICond->getName() + ".not");
3782
3783 // Merge the conditions.
3784 Value *Cond =
3785 createLogicalOp(Builder, Instruction::Or, PBICond, BICond, "brmerge");
3786
3787 // Modify PBI to branch on the new condition to the new dests.
3788 PBI->setCondition(Cond);
3789 PBI->setSuccessor(0, CommonDest);
3790 PBI->setSuccessor(1, OtherDest);
3791
3792 if (DTU) {
3793 Updates.push_back({DominatorTree::Insert, PBI->getParent(), OtherDest});
3794 Updates.push_back({DominatorTree::Delete, PBI->getParent(), RemovedDest});
3795
3796 DTU->applyUpdates(Updates);
3797 }
3798
3799 // Update branch weight for PBI.
3800 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
3801 uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
3802 bool HasWeights =
3803 extractPredSuccWeights(PBI, BI, PredTrueWeight, PredFalseWeight,
3804 SuccTrueWeight, SuccFalseWeight);
3805 if (HasWeights) {
3806 PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3807 PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3808 SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3809 SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3810 // The weight to CommonDest should be PredCommon * SuccTotal +
3811 // PredOther * SuccCommon.
3812 // The weight to OtherDest should be PredOther * SuccOther.
3813 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) +
3814 PredOther * SuccCommon,
3815 PredOther * SuccOther};
3816 // Halve the weights if any of them cannot fit in an uint32_t
3817 FitWeights(NewWeights);
3818
3819 setBranchWeights(PBI, NewWeights[0], NewWeights[1]);
3820 }
3821
3822 // OtherDest may have phi nodes. If so, add an entry from PBI's
3823 // block that are identical to the entries for BI's block.
3824 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
3825
3826 // We know that the CommonDest already had an edge from PBI to
3827 // it. If it has PHIs though, the PHIs may have different
3828 // entries for BB and PBI's BB. If so, insert a select to make
3829 // them agree.
3830 for (PHINode &PN : CommonDest->phis()) {
3831 Value *BIV = PN.getIncomingValueForBlock(BB);
3832 unsigned PBBIdx = PN.getBasicBlockIndex(PBI->getParent());
3833 Value *PBIV = PN.getIncomingValue(PBBIdx);
3834 if (BIV != PBIV) {
3835 // Insert a select in PBI to pick the right value.
3836 SelectInst *NV = cast<SelectInst>(
3837 Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
3838 PN.setIncomingValue(PBBIdx, NV);
3839 // Although the select has the same condition as PBI, the original branch
3840 // weights for PBI do not apply to the new select because the select's
3841 // 'logical' edges are incoming edges of the phi that is eliminated, not
3842 // the outgoing edges of PBI.
3843 if (HasWeights) {
3844 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
3845 uint64_t PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
3846 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
3847 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
3848 // The weight to PredCommonDest should be PredCommon * SuccTotal.
3849 // The weight to PredOtherDest should be PredOther * SuccCommon.
3850 uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther),
3851 PredOther * SuccCommon};
3852
3853 FitWeights(NewWeights);
3854
3855 setBranchWeights(NV, NewWeights[0], NewWeights[1]);
3856 }
3857 }
3858 }
3859
3860 LLVM_DEBUG(dbgs() << "INTO: " << *PBI->getParent())do { } while (false);
3861 LLVM_DEBUG(dbgs() << *PBI->getParent()->getParent())do { } while (false);
3862
3863 // This basic block is probably dead. We know it has at least
3864 // one fewer predecessor.
3865 return true;
3866}
3867
3868// Simplifies a terminator by replacing it with a branch to TrueBB if Cond is
3869// true or to FalseBB if Cond is false.
3870// Takes care of updating the successors and removing the old terminator.
3871// Also makes sure not to introduce new successors by assuming that edges to
3872// non-successor TrueBBs and FalseBBs aren't reachable.
3873bool SimplifyCFGOpt::SimplifyTerminatorOnSelect(Instruction *OldTerm,
3874 Value *Cond, BasicBlock *TrueBB,
3875 BasicBlock *FalseBB,
3876 uint32_t TrueWeight,
3877 uint32_t FalseWeight) {
3878 auto *BB = OldTerm->getParent();
3879 // Remove any superfluous successor edges from the CFG.
3880 // First, figure out which successors to preserve.
3881 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
3882 // successor.
3883 BasicBlock *KeepEdge1 = TrueBB;
3884 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
3885
3886 SmallPtrSet<BasicBlock *, 2> RemovedSuccessors;
3887
3888 // Then remove the rest.
3889 for (BasicBlock *Succ : successors(OldTerm)) {
3890 // Make sure only to keep exactly one copy of each edge.
3891 if (Succ == KeepEdge1)
3892 KeepEdge1 = nullptr;
3893 else if (Succ == KeepEdge2)
3894 KeepEdge2 = nullptr;
3895 else {
3896 Succ->removePredecessor(BB,
3897 /*KeepOneInputPHIs=*/true);
3898
3899 if (Succ != TrueBB && Succ != FalseBB)
3900 RemovedSuccessors.insert(Succ);
3901 }
3902 }
3903
3904 IRBuilder<> Builder(OldTerm);
3905 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
3906
3907 // Insert an appropriate new terminator.
3908 if (!KeepEdge1 && !KeepEdge2) {
3909 if (TrueBB == FalseBB) {
3910 // We were only looking for one successor, and it was present.
3911 // Create an unconditional branch to it.
3912 Builder.CreateBr(TrueBB);
3913 } else {
3914 // We found both of the successors we were looking for.
3915 // Create a conditional branch sharing the condition of the select.
3916 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB);
3917 if (TrueWeight != FalseWeight)
3918 setBranchWeights(NewBI, TrueWeight, FalseWeight);
3919 }
3920 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
3921 // Neither of the selected blocks were successors, so this
3922 // terminator must be unreachable.
3923 new UnreachableInst(OldTerm->getContext(), OldTerm);
3924 } else {
3925 // One of the selected values was a successor, but the other wasn't.
3926 // Insert an unconditional branch to the one that was found;
3927 // the edge to the one that wasn't must be unreachable.
3928 if (!KeepEdge1) {
3929 // Only TrueBB was found.
3930 Builder.CreateBr(TrueBB);
3931 } else {
3932 // Only FalseBB was found.
3933 Builder.CreateBr(FalseBB);
3934 }
3935 }
3936
3937 EraseTerminatorAndDCECond(OldTerm);
3938
3939 if (DTU) {
3940 SmallVector<DominatorTree::UpdateType, 2> Updates;
3941 Updates.reserve(RemovedSuccessors.size());
3942 for (auto *RemovedSuccessor : RemovedSuccessors)
3943 Updates.push_back({DominatorTree::Delete, BB, RemovedSuccessor});
3944 DTU->applyUpdates(Updates);
3945 }
3946
3947 return true;
3948}
3949
3950// Replaces
3951// (switch (select cond, X, Y)) on constant X, Y
3952// with a branch - conditional if X and Y lead to distinct BBs,
3953// unconditional otherwise.
3954bool SimplifyCFGOpt::SimplifySwitchOnSelect(SwitchInst *SI,
3955 SelectInst *Select) {
3956 // Check for constant integer values in the select.
3957 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
3958 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
3959 if (!TrueVal || !FalseVal)
3960 return false;
3961
3962 // Find the relevant condition and destinations.
3963 Value *Condition = Select->getCondition();
3964 BasicBlock *TrueBB = SI->findCaseValue(TrueVal)->getCaseSuccessor();
3965 BasicBlock *FalseBB = SI->findCaseValue(FalseVal)->getCaseSuccessor();
3966
3967 // Get weight for TrueBB and FalseBB.
3968 uint32_t TrueWeight = 0, FalseWeight = 0;
3969 SmallVector<uint64_t, 8> Weights;
3970 bool HasWeights = HasBranchWeights(SI);
3971 if (HasWeights) {
3972 GetBranchWeights(SI, Weights);
3973 if (Weights.size() == 1 + SI->getNumCases()) {
3974 TrueWeight =
3975 (uint32_t)Weights[SI->findCaseValue(TrueVal)->getSuccessorIndex()];
3976 FalseWeight =
3977 (uint32_t)Weights[SI->findCaseValue(FalseVal)->getSuccessorIndex()];
3978 }
3979 }
3980
3981 // Perform the actual simplification.
3982 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, TrueWeight,
3983 FalseWeight);
3984}
3985
3986// Replaces
3987// (indirectbr (select cond, blockaddress(@fn, BlockA),
3988// blockaddress(@fn, BlockB)))
3989// with
3990// (br cond, BlockA, BlockB).
3991bool SimplifyCFGOpt::SimplifyIndirectBrOnSelect(IndirectBrInst *IBI,
3992 SelectInst *SI) {
3993 // Check that both operands of the select are block addresses.
3994 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
3995 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
3996 if (!TBA || !FBA)
3997 return false;
3998
3999 // Extract the actual blocks.
4000 BasicBlock *TrueBB = TBA->getBasicBlock();
4001 BasicBlock *FalseBB = FBA->getBasicBlock();
4002
4003 // Perform the actual simplification.
4004 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 0,
4005 0);
4006}
4007
4008/// This is called when we find an icmp instruction
4009/// (a seteq/setne with a constant) as the only instruction in a
4010/// block that ends with an uncond branch. We are looking for a very specific
4011/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
4012/// this case, we merge the first two "or's of icmp" into a switch, but then the
4013/// default value goes to an uncond block with a seteq in it, we get something
4014/// like:
4015///
4016/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
4017/// DEFAULT:
4018/// %tmp = icmp eq i8 %A, 92
4019/// br label %end
4020/// end:
4021/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
4022///
4023/// We prefer to split the edge to 'end' so that there is a true/false entry to
4024/// the PHI, merging the third icmp into the switch.
4025bool SimplifyCFGOpt::tryToSimplifyUncondBranchWithICmpInIt(
4026 ICmpInst *ICI, IRBuilder<> &Builder) {
4027 BasicBlock *BB = ICI->getParent();
4028
4029 // If the block has any PHIs in it or the icmp has multiple uses, it is too
4030 // complex.
4031 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse())
4032 return false;
4033
4034 Value *V = ICI->getOperand(0);
4035 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
4036
4037 // The pattern we're looking for is where our only predecessor is a switch on
4038 // 'V' and this block is the default case for the switch. In this case we can
4039 // fold the compared value into the switch to simplify things.
4040 BasicBlock *Pred = BB->getSinglePredecessor();
4041 if (!Pred || !isa<SwitchInst>(Pred->getTerminator()))
4042 return false;
4043
4044 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
4045 if (SI->getCondition() != V)
4046 return false;
4047
4048 // If BB is reachable on a non-default case, then we simply know the value of
4049 // V in this block. Substitute it and constant fold the icmp instruction
4050 // away.
4051 if (SI->getDefaultDest() != BB) {
4052 ConstantInt *VVal = SI->findCaseDest(BB);
4053 assert(VVal && "Should have a unique destination value")((void)0);
4054 ICI->setOperand(0, VVal);
4055
4056 if (Value *V = SimplifyInstruction(ICI, {DL, ICI})) {
4057 ICI->replaceAllUsesWith(V);
4058 ICI->eraseFromParent();
4059 }
4060 // BB is now empty, so it is likely to simplify away.
4061 return requestResimplify();
4062 }
4063
4064 // Ok, the block is reachable from the default dest. If the constant we're
4065 // comparing exists in one of the other edges, then we can constant fold ICI
4066 // and zap it.
4067 if (SI->findCaseValue(Cst) != SI->case_default()) {
4068 Value *V;
4069 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
4070 V = ConstantInt::getFalse(BB->getContext());
4071 else
4072 V = ConstantInt::getTrue(BB->getContext());
4073
4074 ICI->replaceAllUsesWith(V);
4075 ICI->eraseFromParent();
4076 // BB is now empty, so it is likely to simplify away.
4077 return requestResimplify();
4078 }
4079
4080 // The use of the icmp has to be in the 'end' block, by the only PHI node in
4081 // the block.
4082 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
4083 PHINode *PHIUse = dyn_cast<PHINode>(ICI->user_back());
4084 if (PHIUse == nullptr || PHIUse != &SuccBlock->front() ||
4085 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
4086 return false;
4087
4088 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
4089 // true in the PHI.
4090 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
4091 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
4092
4093 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
4094 std::swap(DefaultCst, NewCst);
4095
4096 // Replace ICI (which is used by the PHI for the default value) with true or
4097 // false depending on if it is EQ or NE.
4098 ICI->replaceAllUsesWith(DefaultCst);
4099 ICI->eraseFromParent();
4100
4101 SmallVector<DominatorTree::UpdateType, 2> Updates;
4102
4103 // Okay, the switch goes to this block on a default value. Add an edge from
4104 // the switch to the merge point on the compared value.
4105 BasicBlock *NewBB =
4106 BasicBlock::Create(BB->getContext(), "switch.edge", BB->getParent(), BB);
4107 {
4108 SwitchInstProfUpdateWrapper SIW(*SI);
4109 auto W0 = SIW.getSuccessorWeight(0);
4110 SwitchInstProfUpdateWrapper::CaseWeightOpt NewW;
4111 if (W0) {
4112 NewW = ((uint64_t(*W0) + 1) >> 1);
4113 SIW.setSuccessorWeight(0, *NewW);
4114 }
4115 SIW.addCase(Cst, NewBB, NewW);
4116 if (DTU)
4117 Updates.push_back({DominatorTree::Insert, Pred, NewBB});
4118 }
4119
4120 // NewBB branches to the phi block, add the uncond branch and the phi entry.
4121 Builder.SetInsertPoint(NewBB);
4122 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
4123 Builder.CreateBr(SuccBlock);
4124 PHIUse->addIncoming(NewCst, NewBB);
4125 if (DTU) {
4126 Updates.push_back({DominatorTree::Insert, NewBB, SuccBlock});
4127 DTU->applyUpdates(Updates);
4128 }
4129 return true;
4130}
4131
4132/// The specified branch is a conditional branch.
4133/// Check to see if it is branching on an or/and chain of icmp instructions, and
4134/// fold it into a switch instruction if so.
4135bool SimplifyCFGOpt::SimplifyBranchOnICmpChain(BranchInst *BI,
4136 IRBuilder<> &Builder,
4137 const DataLayout &DL) {
4138 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
4139 if (!Cond)
4140 return false;
4141
4142 // Change br (X == 0 | X == 1), T, F into a switch instruction.
4143 // If this is a bunch of seteq's or'd together, or if it's a bunch of
4144 // 'setne's and'ed together, collect them.
4145
4146 // Try to gather values from a chain of and/or to be turned into a switch
4147 ConstantComparesGatherer ConstantCompare(Cond, DL);
4148 // Unpack the result
4149 SmallVectorImpl<ConstantInt *> &Values = ConstantCompare.Vals;
4150 Value *CompVal = ConstantCompare.CompValue;
4151 unsigned UsedICmps = ConstantCompare.UsedICmps;
4152 Value *ExtraCase = ConstantCompare.Extra;
4153
4154 // If we didn't have a multiply compared value, fail.
4155 if (!CompVal)
4156 return false;
4157
4158 // Avoid turning single icmps into a switch.
4159 if (UsedICmps <= 1)
4160 return false;
4161
4162 bool TrueWhenEqual = match(Cond, m_LogicalOr(m_Value(), m_Value()));
4163
4164 // There might be duplicate constants in the list, which the switch
4165 // instruction can't handle, remove them now.
4166 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
4167 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
4168
4169 // If Extra was used, we require at least two switch values to do the
4170 // transformation. A switch with one value is just a conditional branch.
4171 if (ExtraCase && Values.size() < 2)
4172 return false;
4173
4174 // TODO: Preserve branch weight metadata, similarly to how
4175 // FoldValueComparisonIntoPredecessors preserves it.
4176
4177 // Figure out which block is which destination.
4178 BasicBlock *DefaultBB = BI->getSuccessor(1);
4179 BasicBlock *EdgeBB = BI->getSuccessor(0);
4180 if (!TrueWhenEqual)
4181 std::swap(DefaultBB, EdgeBB);
4182
4183 BasicBlock *BB = BI->getParent();
4184
4185 LLVM_DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()do { } while (false)
4186 << " cases into SWITCH. BB is:\n"do { } while (false)
4187 << *BB)do { } while (false);
4188
4189 SmallVector<DominatorTree::UpdateType, 2> Updates;
4190
4191 // If there are any extra values that couldn't be folded into the switch
4192 // then we evaluate them with an explicit branch first. Split the block
4193 // right before the condbr to handle it.
4194 if (ExtraCase) {
4195 BasicBlock *NewBB = SplitBlock(BB, BI, DTU, /*LI=*/nullptr,
4196 /*MSSAU=*/nullptr, "switch.early.test");
4197
4198 // Remove the uncond branch added to the old block.
4199 Instruction *OldTI = BB->getTerminator();
4200 Builder.SetInsertPoint(OldTI);
4201
4202 // There can be an unintended UB if extra values are Poison. Before the
4203 // transformation, extra values may not be evaluated according to the
4204 // condition, and it will not raise UB. But after transformation, we are
4205 // evaluating extra values before checking the condition, and it will raise
4206 // UB. It can be solved by adding freeze instruction to extra values.
4207 AssumptionCache *AC = Options.AC;
4208
4209 if (!isGuaranteedNotToBeUndefOrPoison(ExtraCase, AC, BI, nullptr))
4210 ExtraCase = Builder.CreateFreeze(ExtraCase);
4211
4212 if (TrueWhenEqual)
4213 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
4214 else
4215 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
4216
4217 OldTI->eraseFromParent();
4218
4219 if (DTU)
4220 Updates.push_back({DominatorTree::Insert, BB, EdgeBB});
4221
4222 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
4223 // for the edge we just added.
4224 AddPredecessorToBlock(EdgeBB, BB, NewBB);
4225
4226 LLVM_DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCasedo { } while (false)
4227 << "\nEXTRABB = " << *BB)do { } while (false);
4228 BB = NewBB;
4229 }
4230
4231 Builder.SetInsertPoint(BI);
4232 // Convert pointer to int before we switch.
4233 if (CompVal->getType()->isPointerTy()) {
4234 CompVal = Builder.CreatePtrToInt(
4235 CompVal, DL.getIntPtrType(CompVal->getType()), "magicptr");
4236 }
4237
4238 // Create the new switch instruction now.
4239 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
4240
4241 // Add all of the 'cases' to the switch instruction.
4242 for (unsigned i = 0, e = Values.size(); i != e; ++i)
4243 New->addCase(Values[i], EdgeBB);
4244
4245 // We added edges from PI to the EdgeBB. As such, if there were any
4246 // PHI nodes in EdgeBB, they need entries to be added corresponding to
4247 // the number of edges added.
4248 for (BasicBlock::iterator BBI = EdgeBB->begin(); isa<PHINode>(BBI); ++BBI) {
4249 PHINode *PN = cast<PHINode>(BBI);
4250 Value *InVal = PN->getIncomingValueForBlock(BB);
4251 for (unsigned i = 0, e = Values.size() - 1; i != e; ++i)
4252 PN->addIncoming(InVal, BB);
4253 }
4254
4255 // Erase the old branch instruction.
4256 EraseTerminatorAndDCECond(BI);
4257 if (DTU)
4258 DTU->applyUpdates(Updates);
4259
4260 LLVM_DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n')do { } while (false);
4261 return true;
4262}
4263
4264bool SimplifyCFGOpt::simplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
4265 if (isa<PHINode>(RI->getValue()))
15
Assuming the object is a 'PHINode'
16
Taking true branch
4266 return simplifyCommonResume(RI);
17
Calling 'SimplifyCFGOpt::simplifyCommonResume'
4267 else if (isa<LandingPadInst>(RI->getParent()->getFirstNonPHI()) &&
4268 RI->getValue() == RI->getParent()->getFirstNonPHI())
4269 // The resume must unwind the exception that caused control to branch here.
4270 return simplifySingleResume(RI);
4271
4272 return false;
4273}
4274
4275// Check if cleanup block is empty
4276static bool isCleanupBlockEmpty(iterator_range<BasicBlock::iterator> R) {
4277 for (Instruction &I : R) {
4278 auto *II = dyn_cast<IntrinsicInst>(&I);
4279 if (!II)
4280 return false;
4281
4282 Intrinsic::ID IntrinsicID = II->getIntrinsicID();
4283 switch (IntrinsicID) {
4284 case Intrinsic::dbg_declare:
4285 case Intrinsic::dbg_value:
4286 case Intrinsic::dbg_label:
4287 case Intrinsic::lifetime_end:
4288 break;
4289 default:
4290 return false;
4291 }
4292 }
4293 return true;
19
Returning the value 1, which participates in a condition later
4294}
4295
4296// Simplify resume that is shared by several landing pads (phi of landing pad).
4297bool SimplifyCFGOpt::simplifyCommonResume(ResumeInst *RI) {
4298 BasicBlock *BB = RI->getParent();
4299
4300 // Check that there are no other instructions except for debug and lifetime
4301 // intrinsics between the phi's and resume instruction.
4302 if (!isCleanupBlockEmpty(
18
Calling 'isCleanupBlockEmpty'
20
Returning from 'isCleanupBlockEmpty'
21
Taking false branch
4303 make_range(RI->getParent()->getFirstNonPHI(), BB->getTerminator())))
4304 return false;
4305
4306 SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks;
4307 auto *PhiLPInst = cast<PHINode>(RI->getValue());
22
The object is a 'PHINode'
4308
4309 // Check incoming blocks to see if any of them are trivial.
4310 for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End;
23
Assuming 'Idx' is not equal to 'End'
24
Loop condition is true. Entering loop body
4311 Idx++) {
4312 auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx);
4313 auto *IncomingValue = PhiLPInst->getIncomingValue(Idx);
4314
4315 // If the block has other successors, we can not delete it because
4316 // it has other dependents.
4317 if (IncomingBB->getUniqueSuccessor() != BB)
25
Assuming the condition is false
26
Taking false branch
4318 continue;
4319
4320 auto *LandingPad = dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI());
27
Assuming the object is not a 'LandingPadInst'
28
'LandingPad' initialized to a null pointer value
4321 // Not the landing pad that caused the control to branch here.
4322 if (IncomingValue
28.1
'IncomingValue' is equal to 'LandingPad'
!= LandingPad)
29
Taking false branch
4323 continue;
4324
4325 if (isCleanupBlockEmpty(
4326 make_range(LandingPad->getNextNode(), IncomingBB->getTerminator())))
30
Called C++ object pointer is null
4327 TrivialUnwindBlocks.insert(IncomingBB);
4328 }
4329
4330 // If no trivial unwind blocks, don't do any simplifications.
4331 if (TrivialUnwindBlocks.empty())
4332 return false;
4333
4334 // Turn all invokes that unwind here into calls.
4335 for (auto *TrivialBB : TrivialUnwindBlocks) {
4336 // Blocks that will be simplified should be removed from the phi node.
4337 // Note there could be multiple edges to the resume block, and we need
4338 // to remove them all.
4339 while (PhiLPInst->getBasicBlockIndex(TrivialBB) != -1)
4340 BB->removePredecessor(TrivialBB, true);
4341
4342 for (BasicBlock *Pred :
4343 llvm::make_early_inc_range(predecessors(TrivialBB))) {
4344 removeUnwindEdge(Pred, DTU);
4345 ++NumInvokes;
4346 }
4347
4348 // In each SimplifyCFG run, only the current processed block can be erased.
4349 // Otherwise, it will break the iteration of SimplifyCFG pass. So instead
4350 // of erasing TrivialBB, we only remove the branch to the common resume
4351 // block so that we can later erase the resume block since it has no
4352 // predecessors.
4353 TrivialBB->getTerminator()->eraseFromParent();
4354 new UnreachableInst(RI->getContext(), TrivialBB);
4355 if (DTU)
4356 DTU->applyUpdates({{DominatorTree::Delete, TrivialBB, BB}});
4357 }
4358
4359 // Delete the resume block if all its predecessors have been removed.
4360 if (pred_empty(BB))
4361 DeleteDeadBlock(BB, DTU);
4362
4363 return !TrivialUnwindBlocks.empty();
4364}
4365
4366// Simplify resume that is only used by a single (non-phi) landing pad.
4367bool SimplifyCFGOpt::simplifySingleResume(ResumeInst *RI) {
4368 BasicBlock *BB = RI->getParent();
4369 auto *LPInst = cast<LandingPadInst>(BB->getFirstNonPHI());
4370 assert(RI->getValue() == LPInst &&((void)0)
4371 "Resume must unwind the exception that caused control to here")((void)0);
4372
4373 // Check that there are no other instructions except for debug intrinsics.
4374 if (!isCleanupBlockEmpty(
4375 make_range<Instruction *>(LPInst->getNextNode(), RI)))
4376 return false;
4377
4378 // Turn all invokes that unwind here into calls and delete the basic block.
4379 for (BasicBlock *Pred : llvm::make_early_inc_range(predecessors(BB))) {
4380 removeUnwindEdge(Pred, DTU);
4381 ++NumInvokes;
4382 }
4383
4384 // The landingpad is now unreachable. Zap it.
4385 DeleteDeadBlock(BB, DTU);
4386 return true;
4387}
4388
4389static bool removeEmptyCleanup(CleanupReturnInst *RI, DomTreeUpdater *DTU) {
4390 // If this is a trivial cleanup pad that executes no instructions, it can be
4391 // eliminated. If the cleanup pad continues to the caller, any predecessor
4392 // that is an EH pad will be updated to continue to the caller and any
4393 // predecessor that terminates with an invoke instruction will have its invoke
4394 // instruction converted to a call instruction. If the cleanup pad being
4395 // simplified does not continue to the caller, each predecessor will be
4396 // updated to continue to the unwind destination of the cleanup pad being
4397 // simplified.
4398 BasicBlock *BB = RI->getParent();
4399 CleanupPadInst *CPInst = RI->getCleanupPad();
4400 if (CPInst->getParent() != BB)
4401 // This isn't an empty cleanup.
4402 return false;
4403
4404 // We cannot kill the pad if it has multiple uses. This typically arises
4405 // from unreachable basic blocks.
4406 if (!CPInst->hasOneUse())
4407 return false;
4408
4409 // Check that there are no other instructions except for benign intrinsics.
4410 if (!isCleanupBlockEmpty(
4411 make_range<Instruction *>(CPInst->getNextNode(), RI)))
4412 return false;
4413
4414 // If the cleanup return we are simplifying unwinds to the caller, this will
4415 // set UnwindDest to nullptr.
4416 BasicBlock *UnwindDest = RI->getUnwindDest();
4417 Instruction *DestEHPad = UnwindDest ? UnwindDest->getFirstNonPHI() : nullptr;
4418
4419 // We're about to remove BB from the control flow. Before we do, sink any
4420 // PHINodes into the unwind destination. Doing this before changing the
4421 // control flow avoids some potentially slow checks, since we can currently
4422 // be certain that UnwindDest and BB have no common predecessors (since they
4423 // are both EH pads).
4424 if (UnwindDest) {
4425 // First, go through the PHI nodes in UnwindDest and update any nodes that
4426 // reference the block we are removing
4427 for (PHINode &DestPN : UnwindDest->phis()) {
4428 int Idx = DestPN.getBasicBlockIndex(BB);
4429 // Since BB unwinds to UnwindDest, it has to be in the PHI node.
4430 assert(Idx != -1)((void)0);
4431 // This PHI node has an incoming value that corresponds to a control
4432 // path through the cleanup pad we are removing. If the incoming
4433 // value is in the cleanup pad, it must be a PHINode (because we
4434 // verified above that the block is otherwise empty). Otherwise, the
4435 // value is either a constant or a value that dominates the cleanup
4436 // pad being removed.
4437 //
4438 // Because BB and UnwindDest are both EH pads, all of their
4439 // predecessors must unwind to these blocks, and since no instruction
4440 // can have multiple unwind destinations, there will be no overlap in
4441 // incoming blocks between SrcPN and DestPN.
4442 Value *SrcVal = DestPN.getIncomingValue(Idx);
4443 PHINode *SrcPN = dyn_cast<PHINode>(SrcVal);
4444
4445 bool NeedPHITranslation = SrcPN && SrcPN->getParent() == BB;
4446 for (auto *Pred : predecessors(BB)) {
4447 Value *Incoming =
4448 NeedPHITranslation ? SrcPN->getIncomingValueForBlock(Pred) : SrcVal;
4449 DestPN.addIncoming(Incoming, Pred);
4450 }
4451 }
4452
4453 // Sink any remaining PHI nodes directly into UnwindDest.
4454 Instruction *InsertPt = DestEHPad;
4455 for (PHINode &PN : make_early_inc_range(BB->phis())) {
4456 if (PN.use_empty() || !PN.isUsedOutsideOfBlock(BB))
4457 // If the PHI node has no uses or all of its uses are in this basic
4458 // block (meaning they are debug or lifetime intrinsics), just leave
4459 // it. It will be erased when we erase BB below.
4460 continue;
4461
4462 // Otherwise, sink this PHI node into UnwindDest.
4463 // Any predecessors to UnwindDest which are not already represented
4464 // must be back edges which inherit the value from the path through
4465 // BB. In this case, the PHI value must reference itself.
4466 for (auto *pred : predecessors(UnwindDest))
4467 if (pred != BB)
4468 PN.addIncoming(&PN, pred);
4469 PN.moveBefore(InsertPt);
4470 // Also, add a dummy incoming value for the original BB itself,
4471 // so that the PHI is well-formed until we drop said predecessor.
4472 PN.addIncoming(UndefValue::get(PN.getType()), BB);
4473 }
4474 }
4475
4476 std::vector<DominatorTree::UpdateType> Updates;
4477
4478 // We use make_early_inc_range here because we will remove all predecessors.
4479 for (BasicBlock *PredBB : llvm::make_early_inc_range(predecessors(BB))) {
4480 if (UnwindDest == nullptr) {
4481 if (DTU) {
4482 DTU->applyUpdates(Updates);
4483 Updates.clear();
4484 }
4485 removeUnwindEdge(PredBB, DTU);
4486 ++NumInvokes;
4487 } else {
4488 BB->removePredecessor(PredBB);
4489 Instruction *TI = PredBB->getTerminator();
4490 TI->replaceUsesOfWith(BB, UnwindDest);
4491 if (DTU) {
4492 Updates.push_back({DominatorTree::Insert, PredBB, UnwindDest});
4493 Updates.push_back({DominatorTree::Delete, PredBB, BB});
4494 }
4495 }
4496 }
4497
4498 if (DTU)
4499 DTU->applyUpdates(Updates);
4500
4501 DeleteDeadBlock(BB, DTU);
4502
4503 return true;
4504}
4505
4506// Try to merge two cleanuppads together.
4507static bool mergeCleanupPad(CleanupReturnInst *RI) {
4508 // Skip any cleanuprets which unwind to caller, there is nothing to merge
4509 // with.
4510 BasicBlock *UnwindDest = RI->getUnwindDest();
4511 if (!UnwindDest)
4512 return false;
4513
4514 // This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't
4515 // be safe to merge without code duplication.
4516 if (UnwindDest->getSinglePredecessor() != RI->getParent())
4517 return false;
4518
4519 // Verify that our cleanuppad's unwind destination is another cleanuppad.
4520 auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front());
4521 if (!SuccessorCleanupPad)
4522 return false;
4523
4524 CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad();
4525 // Replace any uses of the successor cleanupad with the predecessor pad
4526 // The only cleanuppad uses should be this cleanupret, it's cleanupret and
4527 // funclet bundle operands.
4528 SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad);
4529 // Remove the old cleanuppad.
4530 SuccessorCleanupPad->eraseFromParent();
4531 // Now, we simply replace the cleanupret with a branch to the unwind
4532 // destination.
4533 BranchInst::Create(UnwindDest, RI->getParent());
4534 RI->eraseFromParent();
4535
4536 return true;
4537}
4538
4539bool SimplifyCFGOpt::simplifyCleanupReturn(CleanupReturnInst *RI) {
4540 // It is possible to transiantly have an undef cleanuppad operand because we
4541 // have deleted some, but not all, dead blocks.
4542 // Eventually, this block will be deleted.
4543 if (isa<UndefValue>(RI->getOperand(0)))
4544 return false;
4545
4546 if (mergeCleanupPad(RI))
4547 return true;
4548
4549 if (removeEmptyCleanup(RI, DTU))
4550 return true;
4551
4552 return false;
4553}
4554
4555// WARNING: keep in sync with InstCombinerImpl::visitUnreachableInst()!
4556bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
4557 BasicBlock *BB = UI->getParent();
4558
4559 bool Changed = false;
4560
4561 // If there are any instructions immediately before the unreachable that can
4562 // be removed, do so.
4563 while (UI->getIterator() != BB->begin()) {
4564 BasicBlock::iterator BBI = UI->getIterator();
4565 --BBI;
4566
4567 if (!isGuaranteedToTransferExecutionToSuccessor(&*BBI))
4568 break; // Can not drop any more instructions. We're done here.
4569 // Otherwise, this instruction can be freely erased,
4570 // even if it is not side-effect free.
4571
4572 // Note that deleting EH's here is in fact okay, although it involves a bit
4573 // of subtle reasoning. If this inst is an EH, all the predecessors of this
4574 // block will be the unwind edges of Invoke/CatchSwitch/CleanupReturn,
4575 // and we can therefore guarantee this block will be erased.
4576
4577 // Delete this instruction (any uses are guaranteed to be dead)
4578 BBI->replaceAllUsesWith(PoisonValue::get(BBI->getType()));
4579 BBI->eraseFromParent();
4580 Changed = true;
4581 }
4582
4583 // If the unreachable instruction is the first in the block, take a gander
4584 // at all of the predecessors of this instruction, and simplify them.
4585 if (&BB->front() != UI)
4586 return Changed;
4587
4588 std::vector<DominatorTree::UpdateType> Updates;
4589
4590 SmallSetVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB));
4591 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
4592 auto *Predecessor = Preds[i];
4593 Instruction *TI = Predecessor->getTerminator();
4594 IRBuilder<> Builder(TI);
4595 if (auto *BI = dyn_cast<BranchInst>(TI)) {
4596 // We could either have a proper unconditional branch,
4597 // or a degenerate conditional branch with matching destinations.
4598 if (all_of(BI->successors(),
4599 [BB](auto *Successor) { return Successor == BB; })) {
4600 new UnreachableInst(TI->getContext(), TI);
4601 TI->eraseFromParent();
4602 Changed = true;
4603 } else {
4604 assert(BI->isConditional() && "Can't get here with an uncond branch.")((void)0);
4605 Value* Cond = BI->getCondition();
4606 assert(BI->getSuccessor(0) != BI->getSuccessor(1) &&((void)0)
4607 "The destinations are guaranteed to be different here.")((void)0);
4608 if (BI->getSuccessor(0) == BB) {
4609 Builder.CreateAssumption(Builder.CreateNot(Cond));
4610 Builder.CreateBr(BI->getSuccessor(1));
4611 } else {
4612 assert(BI->getSuccessor(1) == BB && "Incorrect CFG")((void)0);
4613 Builder.CreateAssumption(Cond);
4614 Builder.CreateBr(BI->getSuccessor(0));
4615 }
4616 EraseTerminatorAndDCECond(BI);
4617 Changed = true;
4618 }
4619 if (DTU)
4620 Updates.push_back({DominatorTree::Delete, Predecessor, BB});
4621 } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
4622 SwitchInstProfUpdateWrapper SU(*SI);
4623 for (auto i = SU->case_begin(), e = SU->case_end(); i != e;) {
4624 if (i->getCaseSuccessor() != BB) {
4625 ++i;
4626 continue;
4627 }
4628 BB->removePredecessor(SU->getParent());
4629 i = SU.removeCase(i);
4630 e = SU->case_end();
4631 Changed = true;
4632 }
4633 // Note that the default destination can't be removed!
4634 if (DTU && SI->getDefaultDest() != BB)
4635 Updates.push_back({DominatorTree::Delete, Predecessor, BB});
4636 } else if (auto *II = dyn_cast<InvokeInst>(TI)) {
4637 if (II->getUnwindDest() == BB) {
4638 if (DTU) {
4639 DTU->applyUpdates(Updates);
4640 Updates.clear();
4641 }
4642 removeUnwindEdge(TI->getParent(), DTU);
4643 Changed = true;
4644 }
4645 } else if (auto *CSI = dyn_cast<CatchSwitchInst>(TI)) {
4646 if (CSI->getUnwindDest() == BB) {
4647 if (DTU) {
4648 DTU->applyUpdates(Updates);
4649 Updates.clear();
4650 }
4651 removeUnwindEdge(TI->getParent(), DTU);
4652 Changed = true;
4653 continue;
4654 }
4655
4656 for (CatchSwitchInst::handler_iterator I = CSI->handler_begin(),
4657 E = CSI->handler_end();
4658 I != E; ++I) {
4659 if (*I == BB) {
4660 CSI->removeHandler(I);
4661 --I;
4662 --E;
4663 Changed = true;
4664 }
4665 }
4666 if (DTU)
4667 Updates.push_back({DominatorTree::Delete, Predecessor, BB});
4668 if (CSI->getNumHandlers() == 0) {
4669 if (CSI->hasUnwindDest()) {
4670 // Redirect all predecessors of the block containing CatchSwitchInst
4671 // to instead branch to the CatchSwitchInst's unwind destination.
4672 if (DTU) {
4673 for (auto *PredecessorOfPredecessor : predecessors(Predecessor)) {
4674 Updates.push_back({DominatorTree::Insert,
4675 PredecessorOfPredecessor,
4676 CSI->getUnwindDest()});
4677 Updates.push_back({DominatorTree::Delete,
4678 PredecessorOfPredecessor, Predecessor});
4679 }
4680 }
4681 Predecessor->replaceAllUsesWith(CSI->getUnwindDest());
4682 } else {
4683 // Rewrite all preds to unwind to caller (or from invoke to call).
4684 if (DTU) {
4685 DTU->applyUpdates(Updates);
4686 Updates.clear();
4687 }
4688 SmallVector<BasicBlock *, 8> EHPreds(predecessors(Predecessor));
4689 for (BasicBlock *EHPred : EHPreds)
4690 removeUnwindEdge(EHPred, DTU);
4691 }
4692 // The catchswitch is no longer reachable.
4693 new UnreachableInst(CSI->getContext(), CSI);
4694 CSI->eraseFromParent();
4695 Changed = true;
4696 }
4697 } else if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
4698 (void)CRI;
4699 assert(CRI->hasUnwindDest() && CRI->getUnwindDest() == BB &&((void)0)
4700 "Expected to always have an unwind to BB.")((void)0);
4701 if (DTU)
4702 Updates.push_back({DominatorTree::Delete, Predecessor, BB});
4703 new UnreachableInst(TI->getContext(), TI);
4704 TI->eraseFromParent();
4705 Changed = true;
4706 }
4707 }
4708
4709 if (DTU)
4710 DTU->applyUpdates(Updates);
4711
4712 // If this block is now dead, remove it.
4713 if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) {
4714 DeleteDeadBlock(BB, DTU);
4715 return true;
4716 }
4717
4718 return Changed;
4719}
4720
4721static bool CasesAreContiguous(SmallVectorImpl<ConstantInt *> &Cases) {
4722 assert(Cases.size() >= 1)((void)0);
4723
4724 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
4725 for (size_t I = 1, E = Cases.size(); I != E; ++I) {
4726 if (Cases[I - 1]->getValue() != Cases[I]->getValue() + 1)
4727 return false;
4728 }
4729 return true;
4730}
4731
4732static void createUnreachableSwitchDefault(SwitchInst *Switch,
4733 DomTreeUpdater *DTU) {
4734 LLVM_DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n")do { } while (false);
4735 auto *BB = Switch->getParent();
4736 BasicBlock *NewDefaultBlock = SplitBlockPredecessors(
4737 Switch->getDefaultDest(), Switch->getParent(), "", DTU);
4738 auto *OrigDefaultBlock = Switch->getDefaultDest();
4739 Switch->setDefaultDest(&*NewDefaultBlock);
4740 if (DTU)
4741 DTU->applyUpdates({{DominatorTree::Insert, BB, &*NewDefaultBlock},
4742 {DominatorTree::Delete, BB, OrigDefaultBlock}});
4743 SplitBlock(&*NewDefaultBlock, &NewDefaultBlock->front(), DTU);
4744 SmallVector<DominatorTree::UpdateType, 2> Updates;
4745 if (DTU)
4746 for (auto *Successor : successors(NewDefaultBlock))
4747 Updates.push_back({DominatorTree::Delete, NewDefaultBlock, Successor});
4748 auto *NewTerminator = NewDefaultBlock->getTerminator();
4749 new UnreachableInst(Switch->getContext(), NewTerminator);
4750 EraseTerminatorAndDCECond(NewTerminator);
4751 if (DTU)
4752 DTU->applyUpdates(Updates);
4753}
4754
4755/// Turn a switch with two reachable destinations into an integer range
4756/// comparison and branch.
4757bool SimplifyCFGOpt::TurnSwitchRangeIntoICmp(SwitchInst *SI,
4758 IRBuilder<> &Builder) {
4759 assert(SI->getNumCases() > 1 && "Degenerate switch?")((void)0);
4760
4761 bool HasDefault =
4762 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4763
4764 auto *BB = SI->getParent();
4765
4766 // Partition the cases into two sets with different destinations.
4767 BasicBlock *DestA = HasDefault ? SI->getDefaultDest() : nullptr;
4768 BasicBlock *DestB = nullptr;
4769 SmallVector<ConstantInt *, 16> CasesA;
4770 SmallVector<ConstantInt *, 16> CasesB;
4771
4772 for (auto Case : SI->cases()) {
4773 BasicBlock *Dest = Case.getCaseSuccessor();
4774 if (!DestA)
4775 DestA = Dest;
4776 if (Dest == DestA) {
4777 CasesA.push_back(Case.getCaseValue());
4778 continue;
4779 }
4780 if (!DestB)
4781 DestB = Dest;
4782 if (Dest == DestB) {
4783 CasesB.push_back(Case.getCaseValue());
4784 continue;
4785 }
4786 return false; // More than two destinations.
4787 }
4788
4789 assert(DestA && DestB &&((void)0)
4790 "Single-destination switch should have been folded.")((void)0);
4791 assert(DestA != DestB)((void)0);
4792 assert(DestB != SI->getDefaultDest())((void)0);
4793 assert(!CasesB.empty() && "There must be non-default cases.")((void)0);
4794 assert(!CasesA.empty() || HasDefault)((void)0);
4795
4796 // Figure out if one of the sets of cases form a contiguous range.
4797 SmallVectorImpl<ConstantInt *> *ContiguousCases = nullptr;
4798 BasicBlock *ContiguousDest = nullptr;
4799 BasicBlock *OtherDest = nullptr;
4800 if (!CasesA.empty() && CasesAreContiguous(CasesA)) {
4801 ContiguousCases = &CasesA;
4802 ContiguousDest = DestA;
4803 OtherDest = DestB;
4804 } else if (CasesAreContiguous(CasesB)) {
4805 ContiguousCases = &CasesB;
4806 ContiguousDest = DestB;
4807 OtherDest = DestA;
4808 } else
4809 return false;
4810
4811 // Start building the compare and branch.
4812
4813 Constant *Offset = ConstantExpr::getNeg(ContiguousCases->back());
4814 Constant *NumCases =
4815 ConstantInt::get(Offset->getType(), ContiguousCases->size());
4816
4817 Value *Sub = SI->getCondition();
4818 if (!Offset->isNullValue())
4819 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName() + ".off");
4820
4821 Value *Cmp;
4822 // If NumCases overflowed, then all possible values jump to the successor.
4823 if (NumCases->isNullValue() && !ContiguousCases->empty())
4824 Cmp = ConstantInt::getTrue(SI->getContext());
4825 else
4826 Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
4827 BranchInst *NewBI = Builder.CreateCondBr(Cmp, ContiguousDest, OtherDest);
4828
4829 // Update weight for the newly-created conditional branch.
4830 if (HasBranchWeights(SI)) {
4831 SmallVector<uint64_t, 8> Weights;
4832 GetBranchWeights(SI, Weights);
4833 if (Weights.size() == 1 + SI->getNumCases()) {
4834 uint64_t TrueWeight = 0;
4835 uint64_t FalseWeight = 0;
4836 for (size_t I = 0, E = Weights.size(); I != E; ++I) {
4837 if (SI->getSuccessor(I) == ContiguousDest)
4838 TrueWeight += Weights[I];
4839 else
4840 FalseWeight += Weights[I];
4841 }
4842 while (TrueWeight > UINT32_MAX0xffffffffU || FalseWeight > UINT32_MAX0xffffffffU) {
4843 TrueWeight /= 2;
4844 FalseWeight /= 2;
4845 }
4846 setBranchWeights(NewBI, TrueWeight, FalseWeight);
4847 }
4848 }
4849
4850 // Prune obsolete incoming values off the successors' PHI nodes.
4851 for (auto BBI = ContiguousDest->begin(); isa<PHINode>(BBI); ++BBI) {
4852 unsigned PreviousEdges = ContiguousCases->size();
4853 if (ContiguousDest == SI->getDefaultDest())
4854 ++PreviousEdges;
4855 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4856 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4857 }
4858 for (auto BBI = OtherDest->begin(); isa<PHINode>(BBI); ++BBI) {
4859 unsigned PreviousEdges = SI->getNumCases() - ContiguousCases->size();
4860 if (OtherDest == SI->getDefaultDest())
4861 ++PreviousEdges;
4862 for (unsigned I = 0, E = PreviousEdges - 1; I != E; ++I)
4863 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
4864 }
4865
4866 // Clean up the default block - it may have phis or other instructions before
4867 // the unreachable terminator.
4868 if (!HasDefault)
4869 createUnreachableSwitchDefault(SI, DTU);
4870
4871 auto *UnreachableDefault = SI->getDefaultDest();
4872
4873 // Drop the switch.
4874 SI->eraseFromParent();
4875
4876 if (!HasDefault && DTU)
4877 DTU->applyUpdates({{DominatorTree::Delete, BB, UnreachableDefault}});
4878
4879 return true;
4880}
4881
4882/// Compute masked bits for the condition of a switch
4883/// and use it to remove dead cases.
4884static bool eliminateDeadSwitchCases(SwitchInst *SI, DomTreeUpdater *DTU,
4885 AssumptionCache *AC,
4886 const DataLayout &DL) {
4887 Value *Cond = SI->getCondition();
4888 unsigned Bits = Cond->getType()->getIntegerBitWidth();
4889 KnownBits Known = computeKnownBits(Cond, DL, 0, AC, SI);
4890
4891 // We can also eliminate cases by determining that their values are outside of
4892 // the limited range of the condition based on how many significant (non-sign)
4893 // bits are in the condition value.
4894 unsigned ExtraSignBits = ComputeNumSignBits(Cond, DL, 0, AC, SI) - 1;
4895 unsigned MaxSignificantBitsInCond = Bits - ExtraSignBits;
4896
4897 // Gather dead cases.
4898 SmallVector<ConstantInt *, 8> DeadCases;
4899 SmallDenseMap<BasicBlock *, int, 8> NumPerSuccessorCases;
4900 for (auto &Case : SI->cases()) {
4901 auto *Successor = Case.getCaseSuccessor();
4902 if (DTU)
4903 ++NumPerSuccessorCases[Successor];
4904 const APInt &CaseVal = Case.getCaseValue()->getValue();
4905 if (Known.Zero.intersects(CaseVal) || !Known.One.isSubsetOf(CaseVal) ||
4906 (CaseVal.getMinSignedBits() > MaxSignificantBitsInCond)) {
4907 DeadCases.push_back(Case.getCaseValue());
4908 if (DTU)
4909 --NumPerSuccessorCases[Successor];
4910 LLVM_DEBUG(dbgs() << "SimplifyCFG: switch case " << CaseValdo { } while (false)
4911 << " is dead.\n")do { } while (false);
4912 }
4913 }
4914
4915 // If we can prove that the cases must cover all possible values, the
4916 // default destination becomes dead and we can remove it. If we know some
4917 // of the bits in the value, we can use that to more precisely compute the
4918 // number of possible unique case values.
4919 bool HasDefault =
4920 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
4921 const unsigned NumUnknownBits =
4922 Bits - (Known.Zero | Known.One).countPopulation();
4923 assert(NumUnknownBits <= Bits)((void)0);
4924 if (HasDefault && DeadCases.empty() &&
4925 NumUnknownBits < 64 /* avoid overflow */ &&
4926 SI->getNumCases() == (1ULL << NumUnknownBits)) {
4927 createUnreachableSwitchDefault(SI, DTU);
4928 return true;
4929 }
4930
4931 if (DeadCases.empty())
4932 return false;
4933
4934 SwitchInstProfUpdateWrapper SIW(*SI);
4935 for (ConstantInt *DeadCase : DeadCases) {
4936 SwitchInst::CaseIt CaseI = SI->findCaseValue(DeadCase);
4937 assert(CaseI != SI->case_default() &&((void)0)
4938 "Case was not found. Probably mistake in DeadCases forming.")((void)0);
4939 // Prune unused values from PHI nodes.
4940 CaseI->getCaseSuccessor()->removePredecessor(SI->getParent());
4941 SIW.removeCase(CaseI);
4942 }
4943
4944 if (DTU) {
4945 std::vector<DominatorTree::UpdateType> Updates;
4946 for (const std::pair<BasicBlock *, int> &I : NumPerSuccessorCases)
4947 if (I.second == 0)
4948 Updates.push_back({DominatorTree::Delete, SI->getParent(), I.first});
4949 DTU->applyUpdates(Updates);
4950 }
4951
4952 return true;
4953}
4954
4955/// If BB would be eligible for simplification by
4956/// TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
4957/// by an unconditional branch), look at the phi node for BB in the successor
4958/// block and see if the incoming value is equal to CaseValue. If so, return
4959/// the phi node, and set PhiIndex to BB's index in the phi node.
4960static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
4961 BasicBlock *BB, int *PhiIndex) {
4962 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
4963 return nullptr; // BB must be empty to be a candidate for simplification.
4964 if (!BB->getSinglePredecessor())
4965 return nullptr; // BB must be dominated by the switch.
4966
4967 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
4968 if (!Branch || !Branch->isUnconditional())
4969 return nullptr; // Terminator must be unconditional branch.
4970
4971 BasicBlock *Succ = Branch->getSuccessor(0);
4972
4973 for (PHINode &PHI : Succ->phis()) {
4974 int Idx = PHI.getBasicBlockIndex(BB);
4975 assert(Idx >= 0 && "PHI has no entry for predecessor?")((void)0);
4976
4977 Value *InValue = PHI.getIncomingValue(Idx);
4978 if (InValue != CaseValue)
4979 continue;
4980
4981 *PhiIndex = Idx;
4982 return &PHI;
4983 }
4984
4985 return nullptr;
4986}
4987
4988/// Try to forward the condition of a switch instruction to a phi node
4989/// dominated by the switch, if that would mean that some of the destination
4990/// blocks of the switch can be folded away. Return true if a change is made.
4991static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
4992 using ForwardingNodesMap = DenseMap<PHINode *, SmallVector<int, 4>>;
4993
4994 ForwardingNodesMap ForwardingNodes;
4995 BasicBlock *SwitchBlock = SI->getParent();
4996 bool Changed = false;
4997 for (auto &Case : SI->cases()) {
4998 ConstantInt *CaseValue = Case.getCaseValue();
4999 BasicBlock *CaseDest = Case.getCaseSuccessor();
5000
5001 // Replace phi operands in successor blocks that are using the constant case
5002 // value rather than the switch condition variable:
5003 // switchbb:
5004 // switch i32 %x, label %default [
5005 // i32 17, label %succ
5006 // ...
5007 // succ:
5008 // %r = phi i32 ... [ 17, %switchbb ] ...
5009 // -->
5010 // %r = phi i32 ... [ %x, %switchbb ] ...
5011
5012 for (PHINode &Phi : CaseDest->phis()) {
5013 // This only works if there is exactly 1 incoming edge from the switch to
5014 // a phi. If there is >1, that means multiple cases of the switch map to 1
5015 // value in the phi, and that phi value is not the switch condition. Thus,
5016 // this transform would not make sense (the phi would be invalid because
5017 // a phi can't have different incoming values from the same block).
5018 int SwitchBBIdx = Phi.getBasicBlockIndex(SwitchBlock);
5019 if (Phi.getIncomingValue(SwitchBBIdx) == CaseValue &&
5020 count(Phi.blocks(), SwitchBlock) == 1) {
5021 Phi.setIncomingValue(SwitchBBIdx, SI->getCondition());
5022 Changed = true;
5023 }
5024 }
5025
5026 // Collect phi nodes that are indirectly using this switch's case constants.
5027 int PhiIdx;
5028 if (auto *Phi = FindPHIForConditionForwarding(CaseValue, CaseDest, &PhiIdx))
5029 ForwardingNodes[Phi].push_back(PhiIdx);
5030 }
5031
5032 for (auto &ForwardingNode : ForwardingNodes) {
5033 PHINode *Phi = ForwardingNode.first;
5034 SmallVectorImpl<int> &Indexes = ForwardingNode.second;
5035 if (Indexes.size() < 2)
5036 continue;
5037
5038 for (int Index : Indexes)
5039 Phi->setIncomingValue(Index, SI->getCondition());
5040 Changed = true;
5041 }
5042
5043 return Changed;
5044}
5045
5046/// Return true if the backend will be able to handle
5047/// initializing an array of constants like C.
5048static bool ValidLookupTableConstant(Constant *C, const TargetTransformInfo &TTI) {
5049 if (C->isThreadDependent())
5050 return false;
5051 if (C->isDLLImportDependent())
5052 return false;
5053
5054 if (!isa<ConstantFP>(C) && !isa<ConstantInt>(C) &&
5055 !isa<ConstantPointerNull>(C) && !isa<GlobalValue>(C) &&
5056 !isa<UndefValue>(C) && !isa<ConstantExpr>(C))
5057 return false;
5058
5059 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
5060 if (!CE->isGEPWithNoNotionalOverIndexing())
5061 return false;
5062 if (!ValidLookupTableConstant(CE->getOperand(0), TTI))
5063 return false;
5064 }
5065
5066 if (!TTI.shouldBuildLookupTablesForConstant(C))
5067 return false;
5068
5069 return true;
5070}
5071
5072/// If V is a Constant, return it. Otherwise, try to look up
5073/// its constant value in ConstantPool, returning 0 if it's not there.
5074static Constant *
5075LookupConstant(Value *V,
5076 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
5077 if (Constant *C = dyn_cast<Constant>(V))
5078 return C;
5079 return ConstantPool.lookup(V);
5080}
5081
5082/// Try to fold instruction I into a constant. This works for
5083/// simple instructions such as binary operations where both operands are
5084/// constant or can be replaced by constants from the ConstantPool. Returns the
5085/// resulting constant on success, 0 otherwise.
5086static Constant *
5087ConstantFold(Instruction *I, const DataLayout &DL,
5088 const SmallDenseMap<Value *, Constant *> &ConstantPool) {
5089 if (SelectInst *Select = dyn_cast<SelectInst>(I)) {
5090 Constant *A = LookupConstant(Select->getCondition(), ConstantPool);
5091 if (!A)
5092 return nullptr;
5093 if (A->isAllOnesValue())
5094 return LookupConstant(Select->getTrueValue(), ConstantPool);
5095 if (A->isNullValue())
5096 return LookupConstant(Select->getFalseValue(), ConstantPool);
5097 return nullptr;
5098 }
5099
5100 SmallVector<Constant *, 4> COps;
5101 for (unsigned N = 0, E = I->getNumOperands(); N != E; ++N) {
5102 if (Constant *A = LookupConstant(I->getOperand(N), ConstantPool))
5103 COps.push_back(A);
5104 else
5105 return nullptr;
5106 }
5107
5108 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
5109 return ConstantFoldCompareInstOperands(Cmp->getPredicate(), COps[0],
5110 COps[1], DL);
5111 }
5112
5113 return ConstantFoldInstOperands(I, COps, DL);
5114}
5115
5116/// Try to determine the resulting constant values in phi nodes
5117/// at the common destination basic block, *CommonDest, for one of the case
5118/// destionations CaseDest corresponding to value CaseVal (0 for the default
5119/// case), of a switch instruction SI.
5120static bool
5121GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
5122 BasicBlock **CommonDest,
5123 SmallVectorImpl<std::pair<PHINode *, Constant *>> &Res,
5124 const DataLayout &DL, const TargetTransformInfo &TTI) {
5125 // The block from which we enter the common destination.
5126 BasicBlock *Pred = SI->getParent();
5127
5128 // If CaseDest is empty except for some side-effect free instructions through
5129 // which we can constant-propagate the CaseVal, continue to its successor.
5130 SmallDenseMap<Value *, Constant *> ConstantPool;
5131 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
5132 for (Instruction &I :CaseDest->instructionsWithoutDebug()) {
5133 if (I.isTerminator()) {
5134 // If the terminator is a simple branch, continue to the next block.
5135 if (I.getNumSuccessors() != 1 || I.isExceptionalTerminator())
5136 return false;
5137 Pred = CaseDest;
5138 CaseDest = I.getSuccessor(0);
5139 } else if (Constant *C = ConstantFold(&I, DL, ConstantPool)) {
5140 // Instruction is side-effect free and constant.
5141
5142 // If the instruction has uses outside this block or a phi node slot for
5143 // the block, it is not safe to bypass the instruction since it would then
5144 // no longer dominate all its uses.
5145 for (auto &Use : I.uses()) {
5146 User *User = Use.getUser();
5147 if (Instruction *I = dyn_cast<Instruction>(User))
5148 if (I->getParent() == CaseDest)
5149 continue;
5150 if (PHINode *Phi = dyn_cast<PHINode>(User))
5151 if (Phi->getIncomingBlock(Use) == CaseDest)
5152 continue;
5153 return false;
5154 }
5155
5156 ConstantPool.insert(std::make_pair(&I, C));
5157 } else {
5158 break;
5159 }
5160 }
5161
5162 // If we did not have a CommonDest before, use the current one.
5163 if (!*CommonDest)
5164 *CommonDest = CaseDest;
5165 // If the destination isn't the common one, abort.
5166 if (CaseDest != *CommonDest)
5167 return false;
5168
5169 // Get the values for this case from phi nodes in the destination block.
5170 for (PHINode &PHI : (*CommonDest)->phis()) {
5171 int Idx = PHI.getBasicBlockIndex(Pred);
5172 if (Idx == -1)
5173 continue;
5174
5175 Constant *ConstVal =
5176 LookupConstant(PHI.getIncomingValue(Idx), ConstantPool);
5177 if (!ConstVal)
5178 return false;
5179
5180 // Be conservative about which kinds of constants we support.
5181 if (!ValidLookupTableConstant(ConstVal, TTI))
5182 return false;
5183
5184 Res.push_back(std::make_pair(&PHI, ConstVal));
5185 }
5186
5187 return Res.size() > 0;
5188}
5189
5190// Helper function used to add CaseVal to the list of cases that generate
5191// Result. Returns the updated number of cases that generate this result.
5192static uintptr_t MapCaseToResult(ConstantInt *CaseVal,
5193 SwitchCaseResultVectorTy &UniqueResults,
5194 Constant *Result) {
5195 for (auto &I : UniqueResults) {
5196 if (I.first == Result) {
5197 I.second.push_back(CaseVal);
5198 return I.second.size();
5199 }
5200 }
5201 UniqueResults.push_back(
5202 std::make_pair(Result, SmallVector<ConstantInt *, 4>(1, CaseVal)));
5203 return 1;
5204}
5205
5206// Helper function that initializes a map containing
5207// results for the PHI node of the common destination block for a switch
5208// instruction. Returns false if multiple PHI nodes have been found or if
5209// there is not a common destination block for the switch.
5210static bool
5211InitializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
5212 SwitchCaseResultVectorTy &UniqueResults,
5213 Constant *&DefaultResult, const DataLayout &DL,
5214 const TargetTransformInfo &TTI,
5215 uintptr_t MaxUniqueResults, uintptr_t MaxCasesPerResult) {
5216 for (auto &I : SI->cases()) {
5217 ConstantInt *CaseVal = I.getCaseValue();
5218
5219 // Resulting value at phi nodes for this case value.
5220 SwitchCaseResultsTy Results;
5221 if (!GetCaseResults(SI, CaseVal, I.getCaseSuccessor(), &CommonDest, Results,
5222 DL, TTI))
5223 return false;
5224
5225 // Only one value per case is permitted.
5226 if (Results.size() > 1)
5227 return false;
5228
5229 // Add the case->result mapping to UniqueResults.
5230 const uintptr_t NumCasesForResult =
5231 MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
5232
5233 // Early out if there are too many cases for this result.
5234 if (NumCasesForResult > MaxCasesPerResult)
5235 return false;
5236
5237 // Early out if there are too many unique results.
5238 if (UniqueResults.size() > MaxUniqueResults)
5239 return false;
5240
5241 // Check the PHI consistency.
5242 if (!PHI)
5243 PHI = Results[0].first;
5244 else if (PHI != Results[0].first)
5245 return false;
5246 }
5247 // Find the default result value.
5248 SmallVector<std::pair<PHINode *, Constant *>, 1> DefaultResults;
5249 BasicBlock *DefaultDest = SI->getDefaultDest();
5250 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest, DefaultResults,
5251 DL, TTI);
5252 // If the default value is not found abort unless the default destination
5253 // is unreachable.
5254 DefaultResult =
5255 DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
5256 if ((!DefaultResult &&
5257 !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
5258 return false;
5259
5260 return true;
5261}
5262
5263// Helper function that checks if it is possible to transform a switch with only
5264// two cases (or two cases + default) that produces a result into a select.
5265// Example:
5266// switch (a) {
5267// case 10: %0 = icmp eq i32 %a, 10
5268// return 10; %1 = select i1 %0, i32 10, i32 4
5269// case 20: ----> %2 = icmp eq i32 %a, 20
5270// return 2; %3 = select i1 %2, i32 2, i32 %1
5271// default:
5272// return 4;
5273// }
5274static Value *ConvertTwoCaseSwitch(const SwitchCaseResultVectorTy &ResultVector,
5275 Constant *DefaultResult, Value *Condition,
5276 IRBuilder<> &Builder) {
5277 // If we are selecting between only two cases transform into a simple
5278 // select or a two-way select if default is possible.
5279 if (ResultVector.size() == 2 && ResultVector[0].second.size() == 1 &&
5280 ResultVector[1].second.size() == 1) {
5281 ConstantInt *const FirstCase = ResultVector[0].second[0];
5282 ConstantInt *const SecondCase = ResultVector[1].second[0];
5283
5284 bool DefaultCanTrigger = DefaultResult;
5285 Value *SelectValue = ResultVector[1].first;
5286 if (DefaultCanTrigger) {
5287 Value *const ValueCompare =
5288 Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
5289 SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
5290 DefaultResult, "switch.select");
5291 }
5292 Value *const ValueCompare =
5293 Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
5294 return Builder.CreateSelect(ValueCompare, ResultVector[0].first,
5295 SelectValue, "switch.select");
5296 }
5297
5298 // Handle the degenerate case where two cases have the same value.
5299 if (ResultVector.size() == 1 && ResultVector[0].second.size() == 2 &&
5300 DefaultResult) {
5301 Value *Cmp1 = Builder.CreateICmpEQ(
5302 Condition, ResultVector[0].second[0], "switch.selectcmp.case1");
5303 Value *Cmp2 = Builder.CreateICmpEQ(
5304 Condition, ResultVector[0].second[1], "switch.selectcmp.case2");
5305 Value *Cmp = Builder.CreateOr(Cmp1, Cmp2, "switch.selectcmp");
5306 return Builder.CreateSelect(Cmp, ResultVector[0].first, DefaultResult);
5307 }
5308
5309 return nullptr;
5310}
5311
5312// Helper function to cleanup a switch instruction that has been converted into
5313// a select, fixing up PHI nodes and basic blocks.
5314static void RemoveSwitchAfterSelectConversion(SwitchInst *SI, PHINode *PHI,
5315 Value *SelectValue,
5316 IRBuilder<> &Builder,
5317 DomTreeUpdater *DTU) {
5318 std::vector<DominatorTree::UpdateType> Updates;
5319
5320 BasicBlock *SelectBB = SI->getParent();
5321 BasicBlock *DestBB = PHI->getParent();
5322
5323 if (DTU && !is_contained(predecessors(DestBB), SelectBB))
5324 Updates.push_back({DominatorTree::Insert, SelectBB, DestBB});
5325 Builder.CreateBr(DestBB);
5326
5327 // Remove the switch.
5328
5329 while (PHI->getBasicBlockIndex(SelectBB) >= 0)
5330 PHI->removeIncomingValue(SelectBB);
5331 PHI->addIncoming(SelectValue, SelectBB);
5332
5333 SmallPtrSet<BasicBlock *, 4> RemovedSuccessors;
5334 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
5335 BasicBlock *Succ = SI->getSuccessor(i);
5336
5337 if (Succ == DestBB)
5338 continue;
5339 Succ->removePredecessor(SelectBB);
5340 if (DTU && RemovedSuccessors.insert(Succ).second)
5341 Updates.push_back({DominatorTree::Delete, SelectBB, Succ});
5342 }
5343 SI->eraseFromParent();
5344 if (DTU)
5345 DTU->applyUpdates(Updates);
5346}
5347
5348/// If the switch is only used to initialize one or more
5349/// phi nodes in a common successor block with only two different
5350/// constant values, replace the switch with select.
5351static bool switchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
5352 DomTreeUpdater *DTU, const DataLayout &DL,
5353 const TargetTransformInfo &TTI) {
5354 Value *const Cond = SI->getCondition();
5355 PHINode *PHI = nullptr;
5356 BasicBlock *CommonDest = nullptr;
5357 Constant *DefaultResult;
5358 SwitchCaseResultVectorTy UniqueResults;
5359 // Collect all the cases that will deliver the same value from the switch.
5360 if (!InitializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
5361 DL, TTI, /*MaxUniqueResults*/2,
5362 /*MaxCasesPerResult*/2))
5363 return false;
5364 assert(PHI != nullptr && "PHI for value select not found")((void)0);
5365
5366 Builder.SetInsertPoint(SI);
5367 Value *SelectValue =
5368 ConvertTwoCaseSwitch(UniqueResults, DefaultResult, Cond, Builder);
5369 if (SelectValue) {
5370 RemoveSwitchAfterSelectConversion(SI, PHI, SelectValue, Builder, DTU);
5371 return true;
5372 }
5373 // The switch couldn't be converted into a select.
5374 return false;
5375}
5376
5377namespace {
5378
5379/// This class represents a lookup table that can be used to replace a switch.
5380class SwitchLookupTable {
5381public:
5382 /// Create a lookup table to use as a switch replacement with the contents
5383 /// of Values, using DefaultValue to fill any holes in the table.
5384 SwitchLookupTable(
5385 Module &M, uint64_t TableSize, ConstantInt *Offset,
5386 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
5387 Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName);
5388
5389 /// Build instructions with Builder to retrieve the value at
5390 /// the position given by Index in the lookup table.
5391 Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
5392
5393 /// Return true if a table with TableSize elements of
5394 /// type ElementType would fit in a target-legal register.
5395 static bool WouldFitInRegister(const DataLayout &DL, uint64_t TableSize,
5396 Type *ElementType);
5397
5398private:
5399 // Depending on the contents of the table, it can be represented in
5400 // different ways.
5401 enum {
5402 // For tables where each element contains the same value, we just have to
5403 // store that single value and return it for each lookup.
5404 SingleValueKind,
5405
5406 // For tables where there is a linear relationship between table index
5407 // and values. We calculate the result with a simple multiplication
5408 // and addition instead of a table lookup.
5409 LinearMapKind,
5410
5411 // For small tables with integer elements, we can pack them into a bitmap
5412 // that fits into a target-legal register. Values are retrieved by
5413 // shift and mask operations.
5414 BitMapKind,
5415
5416 // The table is stored as an array of values. Values are retrieved by load
5417 // instructions from the table.
5418 ArrayKind
5419 } Kind;
5420
5421 // For SingleValueKind, this is the single value.
5422 Constant *SingleValue = nullptr;
5423
5424 // For BitMapKind, this is the bitmap.
5425 ConstantInt *BitMap = nullptr;
5426 IntegerType *BitMapElementTy = nullptr;
5427
5428 // For LinearMapKind, these are the constants used to derive the value.
5429 ConstantInt *LinearOffset = nullptr;
5430 ConstantInt *LinearMultiplier = nullptr;
5431
5432 // For ArrayKind, this is the array.
5433 GlobalVariable *Array = nullptr;
5434};
5435
5436} // end anonymous namespace
5437
5438SwitchLookupTable::SwitchLookupTable(
5439 Module &M, uint64_t TableSize, ConstantInt *Offset,
5440 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values,
5441 Constant *DefaultValue, const DataLayout &DL, const StringRef &FuncName) {
5442 assert(Values.size() && "Can't build lookup table without values!")((void)0);
5443 assert(TableSize >= Values.size() && "Can't fit values in table!")((void)0);
5444
5445 // If all values in the table are equal, this is that value.
5446 SingleValue = Values.begin()->second;
5447
5448 Type *ValueType = Values.begin()->second->getType();
5449
5450 // Build up the table contents.
5451 SmallVector<Constant *, 64> TableContents(TableSize);
5452 for (size_t I = 0, E = Values.size(); I != E; ++I) {
5453 ConstantInt *CaseVal = Values[I].first;
5454 Constant *CaseRes = Values[I].second;
5455 assert(CaseRes->getType() == ValueType)((void)0);
5456
5457 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()).getLimitedValue();
5458 TableContents[Idx] = CaseRes;
5459
5460 if (CaseRes != SingleValue)
5461 SingleValue = nullptr;
5462 }
5463
5464 // Fill in any holes in the table with the default result.
5465 if (Values.size() < TableSize) {
5466 assert(DefaultValue &&((void)0)
5467 "Need a default value to fill the lookup table holes.")((void)0);
5468 assert(DefaultValue->getType() == ValueType)((void)0);
5469 for (uint64_t I = 0; I < TableSize; ++I) {
5470 if (!TableContents[I])
5471 TableContents[I] = DefaultValue;
5472 }
5473
5474 if (DefaultValue != SingleValue)
5475 SingleValue = nullptr;
5476 }
5477
5478 // If each element in the table contains the same value, we only need to store
5479 // that single value.
5480 if (SingleValue) {
5481 Kind = SingleValueKind;
5482 return;
5483 }
5484
5485 // Check if we can derive the value with a linear transformation from the
5486 // table index.
5487 if (isa<IntegerType>(ValueType)) {
5488 bool LinearMappingPossible = true;
5489 APInt PrevVal;
5490 APInt DistToPrev;
5491 assert(TableSize >= 2 && "Should be a SingleValue table.")((void)0);
5492 // Check if there is the same distance between two consecutive values.
5493 for (uint64_t I = 0; I < TableSize; ++I) {
5494 ConstantInt *ConstVal = dyn_cast<ConstantInt>(TableContents[I]);
5495 if (!ConstVal) {
5496 // This is an undef. We could deal with it, but undefs in lookup tables
5497 // are very seldom. It's probably not worth the additional complexity.
5498 LinearMappingPossible = false;
5499 break;
5500 }
5501 const APInt &Val = ConstVal->getValue();
5502 if (I != 0) {
5503 APInt Dist = Val - PrevVal;
5504 if (I == 1) {
5505 DistToPrev = Dist;
5506 } else if (Dist != DistToPrev) {
5507 LinearMappingPossible = false;
5508 break;
5509 }
5510 }
5511 PrevVal = Val;
5512 }
5513 if (LinearMappingPossible) {
5514 LinearOffset = cast<ConstantInt>(TableContents[0]);
5515 LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
5516 Kind = LinearMapKind;
5517 ++NumLinearMaps;
5518 return;
5519 }
5520 }
5521
5522 // If the type is integer and the table fits in a register, build a bitmap.
5523 if (WouldFitInRegister(DL, TableSize, ValueType)) {
5524 IntegerType *IT = cast<IntegerType>(ValueType);
5525 APInt TableInt(TableSize * IT->getBitWidth(), 0);
5526 for (uint64_t I = TableSize; I > 0; --I) {
5527 TableInt <<= IT->getBitWidth();
5528 // Insert values into the bitmap. Undef values are set to zero.
5529 if (!isa<UndefValue>(TableContents[I - 1])) {
5530 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]);
5531 TableInt |= Val->getValue().zext(TableInt.getBitWidth());
5532 }
5533 }
5534 BitMap = ConstantInt::get(M.getContext(), TableInt);
5535 BitMapElementTy = IT;
5536 Kind = BitMapKind;
5537 ++NumBitMaps;
5538 return;
5539 }
5540
5541 // Store the table in an array.
5542 ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
5543 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
5544
5545 Array = new GlobalVariable(M, ArrayTy, /*isConstant=*/true,
5546 GlobalVariable::PrivateLinkage, Initializer,
5547 "switch.table." + FuncName);
5548 Array->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
5549 // Set the alignment to that of an array items. We will be only loading one
5550 // value out of it.
5551 Array->setAlignment(Align(DL.getPrefTypeAlignment(ValueType)));
5552 Kind = ArrayKind;
5553}
5554
5555Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
5556 switch (Kind) {
5557 case SingleValueKind:
5558 return SingleValue;
5559 case LinearMapKind: {
5560 // Derive the result value from the input value.
5561 Value *Result = Builder.CreateIntCast(Index, LinearMultiplier->getType(),
5562 false, "switch.idx.cast");
5563 if (!LinearMultiplier->isOne())
5564 Result = Builder.CreateMul(Result, LinearMultiplier, "switch.idx.mult");
5565 if (!LinearOffset->isZero())
5566 Result = Builder.CreateAdd(Result, LinearOffset, "switch.offset");
5567 return Result;
5568 }
5569 case BitMapKind: {
5570 // Type of the bitmap (e.g. i59).
5571 IntegerType *MapTy = BitMap->getType();
5572
5573 // Cast Index to the same type as the bitmap.
5574 // Note: The Index is <= the number of elements in the table, so
5575 // truncating it to the width of the bitmask is safe.
5576 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast");
5577
5578 // Multiply the shift amount by the element width.
5579 ShiftAmt = Builder.CreateMul(
5580 ShiftAmt, ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()),
5581 "switch.shiftamt");
5582
5583 // Shift down.
5584 Value *DownShifted =
5585 Builder.CreateLShr(BitMap, ShiftAmt, "switch.downshift");
5586 // Mask off.
5587 return Builder.CreateTrunc(DownShifted, BitMapElementTy, "switch.masked");
5588 }
5589 case ArrayKind: {
5590 // Make sure the table index will not overflow when treated as signed.
5591 IntegerType *IT = cast<IntegerType>(Index->getType());
5592 uint64_t TableSize =
5593 Array->getInitializer()->getType()->getArrayNumElements();
5594 if (TableSize > (1ULL << (IT->getBitWidth() - 1)))
5595 Index = Builder.CreateZExt(
5596 Index, IntegerType::get(IT->getContext(), IT->getBitWidth() + 1),
5597 "switch.tableidx.zext");
5598
5599 Value *GEPIndices[] = {Builder.getInt32(0), Index};
5600 Value *GEP = Builder.CreateInBoundsGEP(Array->getValueType(), Array,
5601 GEPIndices, "switch.gep");
5602 return Builder.CreateLoad(
5603 cast<ArrayType>(Array->getValueType())->getElementType(), GEP,
5604 "switch.load");
5605 }
5606 }
5607 llvm_unreachable("Unknown lookup table kind!")__builtin_unreachable();
5608}
5609
5610bool SwitchLookupTable::WouldFitInRegister(const DataLayout &DL,
5611 uint64_t TableSize,
5612 Type *ElementType) {
5613 auto *IT = dyn_cast<IntegerType>(ElementType);
5614 if (!IT)
5615 return false;
5616 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values
5617 // are <= 15, we could try to narrow the type.
5618
5619 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width.
5620 if (TableSize >= UINT_MAX(2147483647 *2U +1U) / IT->getBitWidth())
5621 return false;
5622 return DL.fitsInLegalInteger(TableSize * IT->getBitWidth());
5623}
5624
5625/// Determine whether a lookup table should be built for this switch, based on
5626/// the number of cases, size of the table, and the types of the results.
5627static bool
5628ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
5629 const TargetTransformInfo &TTI, const DataLayout &DL,
5630 const SmallDenseMap<PHINode *, Type *> &ResultTypes) {
5631 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX0xffffffffffffffffULL / 10)
5632 return false; // TableSize overflowed, or mul below might overflow.
5633
5634 bool AllTablesFitInRegister = true;
5635 bool HasIllegalType = false;
5636 for (const auto &I : ResultTypes) {
5637 Type *Ty = I.second;
5638
5639 // Saturate this flag to true.
5640 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty);
5641
5642 // Saturate this flag to false.
5643 AllTablesFitInRegister =
5644 AllTablesFitInRegister &&
5645 SwitchLookupTable::WouldFitInRegister(DL, TableSize, Ty);
5646
5647 // If both flags saturate, we're done. NOTE: This *only* works with
5648 // saturating flags, and all flags have to saturate first due to the
5649 // non-deterministic behavior of iterating over a dense map.
5650 if (HasIllegalType && !AllTablesFitInRegister)
5651 break;
5652 }
5653
5654 // If each table would fit in a register, we should build it anyway.
5655 if (AllTablesFitInRegister)
5656 return true;
5657
5658 // Don't build a table that doesn't fit in-register if it has illegal types.
5659 if (HasIllegalType)
5660 return false;
5661
5662 // The table density should be at least 40%. This is the same criterion as for
5663 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
5664 // FIXME: Find the best cut-off.
5665 return SI->getNumCases() * 10 >= TableSize * 4;
5666}
5667
5668/// Try to reuse the switch table index compare. Following pattern:
5669/// \code
5670/// if (idx < tablesize)
5671/// r = table[idx]; // table does not contain default_value
5672/// else
5673/// r = default_value;
5674/// if (r != default_value)
5675/// ...
5676/// \endcode
5677/// Is optimized to:
5678/// \code
5679/// cond = idx < tablesize;
5680/// if (cond)
5681/// r = table[idx];
5682/// else
5683/// r = default_value;
5684/// if (cond)
5685/// ...
5686/// \endcode
5687/// Jump threading will then eliminate the second if(cond).
5688static void reuseTableCompare(
5689 User *PhiUser, BasicBlock *PhiBlock, BranchInst *RangeCheckBranch,
5690 Constant *DefaultValue,
5691 const SmallVectorImpl<std::pair<ConstantInt *, Constant *>> &Values) {
5692 ICmpInst *CmpInst = dyn_cast<ICmpInst>(PhiUser);
5693 if (!CmpInst)
5694 return;
5695
5696 // We require that the compare is in the same block as the phi so that jump
5697 // threading can do its work afterwards.
5698 if (CmpInst->getParent() != PhiBlock)
5699 return;
5700
5701 Constant *CmpOp1 = dyn_cast<Constant>(CmpInst->getOperand(1));
5702 if (!CmpOp1)
5703 return;
5704
5705 Value *RangeCmp = RangeCheckBranch->getCondition();
5706 Constant *TrueConst = ConstantInt::getTrue(RangeCmp->getType());
5707 Constant *FalseConst = ConstantInt::getFalse(RangeCmp->getType());
5708
5709 // Check if the compare with the default value is constant true or false.
5710 Constant *DefaultConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5711 DefaultValue, CmpOp1, true);
5712 if (DefaultConst != TrueConst && DefaultConst != FalseConst)
5713 return;
5714
5715 // Check if the compare with the case values is distinct from the default
5716 // compare result.
5717 for (auto ValuePair : Values) {
5718 Constant *CaseConst = ConstantExpr::getICmp(CmpInst->getPredicate(),
5719 ValuePair.second, CmpOp1, true);
5720 if (!CaseConst || CaseConst == DefaultConst || isa<UndefValue>(CaseConst))
5721 return;
5722 assert((CaseConst == TrueConst || CaseConst == FalseConst) &&((void)0)
5723 "Expect true or false as compare result.")((void)0);
5724 }
5725
5726 // Check if the branch instruction dominates the phi node. It's a simple
5727 // dominance check, but sufficient for our needs.
5728 // Although this check is invariant in the calling loops, it's better to do it
5729 // at this late stage. Practically we do it at most once for a switch.
5730 BasicBlock *BranchBlock = RangeCheckBranch->getParent();
5731 for (BasicBlock *Pred : predecessors(PhiBlock)) {
5732 if (Pred != BranchBlock && Pred->getUniquePredecessor() != BranchBlock)
5733 return;
5734 }
5735
5736 if (DefaultConst == FalseConst) {
5737 // The compare yields the same result. We can replace it.
5738 CmpInst->replaceAllUsesWith(RangeCmp);
5739 ++NumTableCmpReuses;
5740 } else {
5741 // The compare yields the same result, just inverted. We can replace it.
5742 Value *InvertedTableCmp = BinaryOperator::CreateXor(
5743 RangeCmp, ConstantInt::get(RangeCmp->getType(), 1), "inverted.cmp",
5744 RangeCheckBranch);
5745 CmpInst->replaceAllUsesWith(InvertedTableCmp);
5746 ++NumTableCmpReuses;
5747 }
5748}
5749
5750/// If the switch is only used to initialize one or more phi nodes in a common
5751/// successor block with different constant values, replace the switch with
5752/// lookup tables.
5753static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
5754 DomTreeUpdater *DTU, const DataLayout &DL,
5755 const TargetTransformInfo &TTI) {
5756 assert(SI->getNumCases() > 1 && "Degenerate switch?")((void)0);
5757
5758 BasicBlock *BB = SI->getParent();
5759 Function *Fn = BB->getParent();
5760 // Only build lookup table when we have a target that supports it or the
5761 // attribute is not set.
5762 if (!TTI.shouldBuildLookupTables() ||
5763 (Fn->getFnAttribute("no-jump-tables").getValueAsBool()))
5764 return false;
5765
5766 // FIXME: If the switch is too sparse for a lookup table, perhaps we could
5767 // split off a dense part and build a lookup table for that.
5768
5769 // FIXME: This creates arrays of GEPs to constant strings, which means each
5770 // GEP needs a runtime relocation in PIC code. We should just build one big
5771 // string and lookup indices into that.
5772
5773 // Ignore switches with less than three cases. Lookup tables will not make
5774 // them faster, so we don't analyze them.
5775 if (SI->getNumCases() < 3)
5776 return false;
5777
5778 // Figure out the corresponding result for each case value and phi node in the
5779 // common destination, as well as the min and max case values.
5780 assert(!SI->cases().empty())((void)0);
5781 SwitchInst::CaseIt CI = SI->case_begin();
5782 ConstantInt *MinCaseVal = CI->getCaseValue();
5783 ConstantInt *MaxCaseVal = CI->getCaseValue();
5784
5785 BasicBlock *CommonDest = nullptr;
5786
5787 using ResultListTy = SmallVector<std::pair<ConstantInt *, Constant *>, 4>;
5788 SmallDenseMap<PHINode *, ResultListTy> ResultLists;
5789
5790 SmallDenseMap<PHINode *, Constant *> DefaultResults;
5791 SmallDenseMap<PHINode *, Type *> ResultTypes;
5792 SmallVector<PHINode *, 4> PHIs;
5793
5794 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
5795 ConstantInt *CaseVal = CI->getCaseValue();
5796 if (CaseVal->getValue().slt(MinCaseVal->getValue()))
5797 MinCaseVal = CaseVal;
5798 if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
5799 MaxCaseVal = CaseVal;
5800
5801 // Resulting value at phi nodes for this case value.
5802 using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
5803 ResultsTy Results;
5804 if (!GetCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
5805 Results, DL, TTI))
5806 return false;
5807
5808 // Append the result from this case to the list for each phi.
5809 for (const auto &I : Results) {
5810 PHINode *PHI = I.first;
5811 Constant *Value = I.second;
5812 if (!ResultLists.count(PHI))
5813 PHIs.push_back(PHI);
5814 ResultLists[PHI].push_back(std::make_pair(CaseVal, Value));
5815 }
5816 }
5817
5818 // Keep track of the result types.
5819 for (PHINode *PHI : PHIs) {
5820 ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
5821 }
5822
5823 uint64_t NumResults = ResultLists[PHIs[0]].size();
5824 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
5825 uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
5826 bool TableHasHoles = (NumResults < TableSize);
5827
5828 // If the table has holes, we need a constant result for the default case
5829 // or a bitmask that fits in a register.
5830 SmallVector<std::pair<PHINode *, Constant *>, 4> DefaultResultsList;
5831 bool HasDefaultResults =
5832 GetCaseResults(SI, nullptr, SI->getDefaultDest(), &CommonDest,
5833 DefaultResultsList, DL, TTI);
5834
5835 bool NeedMask = (TableHasHoles && !HasDefaultResults);
5836 if (NeedMask) {
5837 // As an extra penalty for the validity test we require more cases.
5838 if (SI->getNumCases() < 4) // FIXME: Find best threshold value (benchmark).
5839 return false;
5840 if (!DL.fitsInLegalInteger(TableSize))
5841 return false;
5842 }
5843
5844 for (const auto &I : DefaultResultsList) {
5845 PHINode *PHI = I.first;
5846 Constant *Result = I.second;
5847 DefaultResults[PHI] = Result;
5848 }
5849
5850 if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
5851 return false;
5852
5853 std::vector<DominatorTree::UpdateType> Updates;
5854
5855 // Create the BB that does the lookups.
5856 Module &Mod = *CommonDest->getParent()->getParent();
5857 BasicBlock *LookupBB = BasicBlock::Create(
5858 Mod.getContext(), "switch.lookup", CommonDest->getParent(), CommonDest);
5859
5860 // Compute the table index value.
5861 Builder.SetInsertPoint(SI);
5862 Value *TableIndex;
5863 if (MinCaseVal->isNullValue())
5864 TableIndex = SI->getCondition();
5865 else
5866 TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal,
5867 "switch.tableidx");
5868
5869 // Compute the maximum table size representable by the integer type we are
5870 // switching upon.
5871 unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
5872 uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX0xffffffffffffffffULL : 1ULL << CaseSize;
5873 assert(MaxTableSize >= TableSize &&((void)0)
5874 "It is impossible for a switch to have more entries than the max "((void)0)
5875 "representable value of its input integer type's size.")((void)0);
5876
5877 // If the default destination is unreachable, or if the lookup table covers
5878 // all values of the conditional variable, branch directly to the lookup table
5879 // BB. Otherwise, check that the condition is within the case range.
5880 const bool DefaultIsReachable =
5881 !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
5882 const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
5883 BranchInst *RangeCheckBranch = nullptr;
5884
5885 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5886 Builder.CreateBr(LookupBB);
5887 if (DTU)
5888 Updates.push_back({DominatorTree::Insert, BB, LookupBB});
5889 // Note: We call removeProdecessor later since we need to be able to get the
5890 // PHI value for the default case in case we're using a bit mask.
5891 } else {
5892 Value *Cmp = Builder.CreateICmpULT(
5893 TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize));
5894 RangeCheckBranch =
5895 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
5896 if (DTU)
5897 Updates.push_back({DominatorTree::Insert, BB, LookupBB});
5898 }
5899
5900 // Populate the BB that does the lookups.
5901 Builder.SetInsertPoint(LookupBB);
5902
5903 if (NeedMask) {
5904 // Before doing the lookup, we do the hole check. The LookupBB is therefore
5905 // re-purposed to do the hole check, and we create a new LookupBB.
5906 BasicBlock *MaskBB = LookupBB;
5907 MaskBB->setName("switch.hole_check");
5908 LookupBB = BasicBlock::Create(Mod.getContext(), "switch.lookup",
5909 CommonDest->getParent(), CommonDest);
5910
5911 // Make the mask's bitwidth at least 8-bit and a power-of-2 to avoid
5912 // unnecessary illegal types.
5913 uint64_t TableSizePowOf2 = NextPowerOf2(std::max(7ULL, TableSize - 1ULL));
5914 APInt MaskInt(TableSizePowOf2, 0);
5915 APInt One(TableSizePowOf2, 1);
5916 // Build bitmask; fill in a 1 bit for every case.
5917 const ResultListTy &ResultList = ResultLists[PHIs[0]];
5918 for (size_t I = 0, E = ResultList.size(); I != E; ++I) {
5919 uint64_t Idx = (ResultList[I].first->getValue() - MinCaseVal->getValue())
5920 .getLimitedValue();
5921 MaskInt |= One << Idx;
5922 }
5923 ConstantInt *TableMask = ConstantInt::get(Mod.getContext(), MaskInt);
5924
5925 // Get the TableIndex'th bit of the bitmask.
5926 // If this bit is 0 (meaning hole) jump to the default destination,
5927 // else continue with table lookup.
5928 IntegerType *MapTy = TableMask->getType();
5929 Value *MaskIndex =
5930 Builder.CreateZExtOrTrunc(TableIndex, MapTy, "switch.maskindex");
5931 Value *Shifted = Builder.CreateLShr(TableMask, MaskIndex, "switch.shifted");
5932 Value *LoBit = Builder.CreateTrunc(
5933 Shifted, Type::getInt1Ty(Mod.getContext()), "switch.lobit");
5934 Builder.CreateCondBr(LoBit, LookupBB, SI->getDefaultDest());
5935 if (DTU) {
5936 Updates.push_back({DominatorTree::Insert, MaskBB, LookupBB});
5937 Updates.push_back({DominatorTree::Insert, MaskBB, SI->getDefaultDest()});
5938 }
5939 Builder.SetInsertPoint(LookupBB);
5940 AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, BB);
5941 }
5942
5943 if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
5944 // We cached PHINodes in PHIs. To avoid accessing deleted PHINodes later,
5945 // do not delete PHINodes here.
5946 SI->getDefaultDest()->removePredecessor(BB,
5947 /*KeepOneInputPHIs=*/true);
5948 if (DTU)
5949 Updates.push_back({DominatorTree::Delete, BB, SI->getDefaultDest()});
5950 }
5951
5952 for (PHINode *PHI : PHIs) {
5953 const ResultListTy &ResultList = ResultLists[PHI];
5954
5955 // If using a bitmask, use any value to fill the lookup table holes.
5956 Constant *DV = NeedMask ? ResultLists[PHI][0].second : DefaultResults[PHI];
5957 StringRef FuncName = Fn->getName();
5958 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultList, DV, DL,
5959 FuncName);
5960
5961 Value *Result = Table.BuildLookup(TableIndex, Builder);
5962
5963 // Do a small peephole optimization: re-use the switch table compare if
5964 // possible.
5965 if (!TableHasHoles && HasDefaultResults && RangeCheckBranch) {
5966 BasicBlock *PhiBlock = PHI->getParent();
5967 // Search for compare instructions which use the phi.
5968 for (auto *User : PHI->users()) {
5969 reuseTableCompare(User, PhiBlock, RangeCheckBranch, DV, ResultList);
5970 }
5971 }
5972
5973 PHI->addIncoming(Result, LookupBB);
5974 }
5975
5976 Builder.CreateBr(CommonDest);
5977 if (DTU)
5978 Updates.push_back({DominatorTree::Insert, LookupBB, CommonDest});
5979
5980 // Remove the switch.
5981 SmallPtrSet<BasicBlock *, 8> RemovedSuccessors;
5982 for (unsigned i = 0, e = SI->getNumSuccessors(); i < e; ++i) {
5983 BasicBlock *Succ = SI->getSuccessor(i);
5984
5985 if (Succ == SI->getDefaultDest())
5986 continue;
5987 Succ->removePredecessor(BB);
5988 RemovedSuccessors.insert(Succ);
5989 }
5990 SI->eraseFromParent();
5991
5992 if (DTU) {
5993 for (BasicBlock *RemovedSuccessor : RemovedSuccessors)
5994 Updates.push_back({DominatorTree::Delete, BB, RemovedSuccessor});
5995 DTU->applyUpdates(Updates);
5996 }
5997
5998 ++NumLookupTables;
5999 if (NeedMask)
6000 ++NumLookupTablesHoles;
6001 return true;
6002}
6003
6004