1 //===- InstSimplifyPass.cpp -----------------------------------------------===//
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 #include "llvm/Transforms/Scalar/InstSimplifyPass.h"
10 #include "llvm/ADT/DepthFirstIterator.h"
11 #include "llvm/ADT/SmallPtrSet.h"
12 #include "llvm/ADT/Statistic.h"
13 #include "llvm/Analysis/AssumptionCache.h"
14 #include "llvm/Analysis/InstructionSimplify.h"
15 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
16 #include "llvm/Analysis/TargetLibraryInfo.h"
17 #include "llvm/IR/DataLayout.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/Type.h"
21 #include "llvm/InitializePasses.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Transforms/Scalar.h"
24 #include "llvm/Transforms/Utils.h"
25 #include "llvm/Transforms/Utils/Local.h"
26
27 using namespace llvm;
28
29 #define DEBUG_TYPE "instsimplify"
30
31 STATISTIC(NumSimplified, "Number of redundant instructions removed");
32
runImpl(Function & F,const SimplifyQuery & SQ,OptimizationRemarkEmitter * ORE)33 static bool runImpl(Function &F, const SimplifyQuery &SQ,
34 OptimizationRemarkEmitter *ORE) {
35 SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
36 bool Changed = false;
37
38 do {
39 for (BasicBlock &BB : F) {
40 // Unreachable code can take on strange forms that we are not prepared to
41 // handle. For example, an instruction may have itself as an operand.
42 if (!SQ.DT->isReachableFromEntry(&BB))
43 continue;
44
45 SmallVector<WeakTrackingVH, 8> DeadInstsInBB;
46 for (Instruction &I : BB) {
47 // The first time through the loop, ToSimplify is empty and we try to
48 // simplify all instructions. On later iterations, ToSimplify is not
49 // empty and we only bother simplifying instructions that are in it.
50 if (!ToSimplify->empty() && !ToSimplify->count(&I))
51 continue;
52
53 // Don't waste time simplifying dead/unused instructions.
54 if (isInstructionTriviallyDead(&I)) {
55 DeadInstsInBB.push_back(&I);
56 Changed = true;
57 } else if (!I.use_empty()) {
58 if (Value *V = SimplifyInstruction(&I, SQ, ORE)) {
59 // Mark all uses for resimplification next time round the loop.
60 for (User *U : I.users())
61 Next->insert(cast<Instruction>(U));
62 I.replaceAllUsesWith(V);
63 ++NumSimplified;
64 Changed = true;
65 // A call can get simplified, but it may not be trivially dead.
66 if (isInstructionTriviallyDead(&I))
67 DeadInstsInBB.push_back(&I);
68 }
69 }
70 }
71 RecursivelyDeleteTriviallyDeadInstructions(DeadInstsInBB, SQ.TLI);
72 }
73
74 // Place the list of instructions to simplify on the next loop iteration
75 // into ToSimplify.
76 std::swap(ToSimplify, Next);
77 Next->clear();
78 } while (!ToSimplify->empty());
79
80 return Changed;
81 }
82
83 namespace {
84 struct InstSimplifyLegacyPass : public FunctionPass {
85 static char ID; // Pass identification, replacement for typeid
InstSimplifyLegacyPass__anon70badb250111::InstSimplifyLegacyPass86 InstSimplifyLegacyPass() : FunctionPass(ID) {
87 initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
88 }
89
getAnalysisUsage__anon70badb250111::InstSimplifyLegacyPass90 void getAnalysisUsage(AnalysisUsage &AU) const override {
91 AU.setPreservesCFG();
92 AU.addRequired<DominatorTreeWrapperPass>();
93 AU.addRequired<AssumptionCacheTracker>();
94 AU.addRequired<TargetLibraryInfoWrapperPass>();
95 AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
96 }
97
98 /// Remove instructions that simplify.
runOnFunction__anon70badb250111::InstSimplifyLegacyPass99 bool runOnFunction(Function &F) override {
100 if (skipFunction(F))
101 return false;
102
103 const DominatorTree *DT =
104 &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
105 const TargetLibraryInfo *TLI =
106 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
107 AssumptionCache *AC =
108 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
109 OptimizationRemarkEmitter *ORE =
110 &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
111 const DataLayout &DL = F.getParent()->getDataLayout();
112 const SimplifyQuery SQ(DL, TLI, DT, AC);
113 return runImpl(F, SQ, ORE);
114 }
115 };
116 } // namespace
117
118 char InstSimplifyLegacyPass::ID = 0;
119 INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",
120 "Remove redundant instructions", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)121 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
122 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
123 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
124 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
125 INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",
126 "Remove redundant instructions", false, false)
127
128 // Public interface to the simplify instructions pass.
129 FunctionPass *llvm::createInstSimplifyLegacyPass() {
130 return new InstSimplifyLegacyPass();
131 }
132
run(Function & F,FunctionAnalysisManager & AM)133 PreservedAnalyses InstSimplifyPass::run(Function &F,
134 FunctionAnalysisManager &AM) {
135 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
136 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
137 auto &AC = AM.getResult<AssumptionAnalysis>(F);
138 auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
139 const DataLayout &DL = F.getParent()->getDataLayout();
140 const SimplifyQuery SQ(DL, &TLI, &DT, &AC);
141 bool Changed = runImpl(F, SQ, &ORE);
142 if (!Changed)
143 return PreservedAnalyses::all();
144
145 PreservedAnalyses PA;
146 PA.preserveSet<CFGAnalyses>();
147 return PA;
148 }
149