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/Utils.h" 24 #include "llvm/Transforms/Utils/Local.h" 25 using namespace llvm; 26 27 #define DEBUG_TYPE "instsimplify" 28 29 STATISTIC(NumSimplified, "Number of redundant instructions removed"); 30 31 static bool runImpl(Function &F, const SimplifyQuery &SQ, 32 OptimizationRemarkEmitter *ORE) { 33 SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 34 bool Changed = false; 35 36 do { 37 for (BasicBlock &BB : F) { 38 // Unreachable code can take on strange forms that we are not prepared to 39 // handle. For example, an instruction may have itself as an operand. 40 if (!SQ.DT->isReachableFromEntry(&BB)) 41 continue; 42 43 SmallVector<WeakTrackingVH, 8> DeadInstsInBB; 44 for (Instruction &I : BB) { 45 // The first time through the loop, ToSimplify is empty and we try to 46 // simplify all instructions. On later iterations, ToSimplify is not 47 // empty and we only bother simplifying instructions that are in it. 48 if (!ToSimplify->empty() && !ToSimplify->count(&I)) 49 continue; 50 51 // Don't waste time simplifying dead/unused instructions. 52 if (isInstructionTriviallyDead(&I)) { 53 DeadInstsInBB.push_back(&I); 54 Changed = true; 55 } else if (!I.use_empty()) { 56 if (Value *V = SimplifyInstruction(&I, SQ, ORE)) { 57 // Mark all uses for resimplification next time round the loop. 58 for (User *U : I.users()) 59 Next->insert(cast<Instruction>(U)); 60 I.replaceAllUsesWith(V); 61 ++NumSimplified; 62 Changed = true; 63 // A call can get simplified, but it may not be trivially dead. 64 if (isInstructionTriviallyDead(&I)) 65 DeadInstsInBB.push_back(&I); 66 } 67 } 68 } 69 RecursivelyDeleteTriviallyDeadInstructions(DeadInstsInBB, SQ.TLI); 70 } 71 72 // Place the list of instructions to simplify on the next loop iteration 73 // into ToSimplify. 74 std::swap(ToSimplify, Next); 75 Next->clear(); 76 } while (!ToSimplify->empty()); 77 78 return Changed; 79 } 80 81 namespace { 82 struct InstSimplifyLegacyPass : public FunctionPass { 83 static char ID; // Pass identification, replacement for typeid 84 InstSimplifyLegacyPass() : FunctionPass(ID) { 85 initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry()); 86 } 87 88 void getAnalysisUsage(AnalysisUsage &AU) const override { 89 AU.setPreservesCFG(); 90 AU.addRequired<DominatorTreeWrapperPass>(); 91 AU.addRequired<AssumptionCacheTracker>(); 92 AU.addRequired<TargetLibraryInfoWrapperPass>(); 93 AU.addRequired<OptimizationRemarkEmitterWrapperPass>(); 94 } 95 96 /// Remove instructions that simplify. 97 bool runOnFunction(Function &F) override { 98 if (skipFunction(F)) 99 return false; 100 101 const DominatorTree *DT = 102 &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 103 const TargetLibraryInfo *TLI = 104 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); 105 AssumptionCache *AC = 106 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); 107 OptimizationRemarkEmitter *ORE = 108 &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE(); 109 const DataLayout &DL = F.getParent()->getDataLayout(); 110 const SimplifyQuery SQ(DL, TLI, DT, AC); 111 return runImpl(F, SQ, ORE); 112 } 113 }; 114 } // namespace 115 116 char InstSimplifyLegacyPass::ID = 0; 117 INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify", 118 "Remove redundant instructions", false, false) 119 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 120 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 121 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 122 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass) 123 INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify", 124 "Remove redundant instructions", false, false) 125 126 // Public interface to the simplify instructions pass. 127 FunctionPass *llvm::createInstSimplifyLegacyPass() { 128 return new InstSimplifyLegacyPass(); 129 } 130 131 PreservedAnalyses InstSimplifyPass::run(Function &F, 132 FunctionAnalysisManager &AM) { 133 auto &DT = AM.getResult<DominatorTreeAnalysis>(F); 134 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); 135 auto &AC = AM.getResult<AssumptionAnalysis>(F); 136 auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F); 137 const DataLayout &DL = F.getParent()->getDataLayout(); 138 const SimplifyQuery SQ(DL, &TLI, &DT, &AC); 139 bool Changed = runImpl(F, SQ, &ORE); 140 if (!Changed) 141 return PreservedAnalyses::all(); 142 143 PreservedAnalyses PA; 144 PA.preserveSet<CFGAnalyses>(); 145 return PA; 146 } 147