138 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8 9#include "llvm/Transforms/Scalar/InstSimplifyPass.h"10#include "llvm/ADT/SmallPtrSet.h"11#include "llvm/ADT/Statistic.h"12#include "llvm/Analysis/AssumptionCache.h"13#include "llvm/Analysis/InstructionSimplify.h"14#include "llvm/Analysis/TargetLibraryInfo.h"15#include "llvm/IR/Dominators.h"16#include "llvm/IR/Function.h"17#include "llvm/InitializePasses.h"18#include "llvm/Pass.h"19#include "llvm/Transforms/Scalar.h"20#include "llvm/Transforms/Utils/Local.h"21 22using namespace llvm;23 24#define DEBUG_TYPE "instsimplify"25 26STATISTIC(NumSimplified, "Number of redundant instructions removed");27 28static bool runImpl(Function &F, const SimplifyQuery &SQ) {29 SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;30 bool Changed = false;31 32 do {33 for (BasicBlock &BB : F) {34 // Unreachable code can take on strange forms that we are not prepared to35 // handle. For example, an instruction may have itself as an operand.36 if (!SQ.DT->isReachableFromEntry(&BB))37 continue;38 39 SmallVector<WeakTrackingVH, 8> DeadInstsInBB;40 for (Instruction &I : BB) {41 // The first time through the loop, ToSimplify is empty and we try to42 // simplify all instructions. On later iterations, ToSimplify is not43 // empty and we only bother simplifying instructions that are in it.44 if (!ToSimplify->empty() && !ToSimplify->count(&I))45 continue;46 47 // Don't waste time simplifying dead/unused instructions.48 if (isInstructionTriviallyDead(&I)) {49 DeadInstsInBB.push_back(&I);50 Changed = true;51 } else if (!I.use_empty()) {52 if (Value *V = simplifyInstruction(&I, SQ)) {53 // Mark all uses for resimplification next time round the loop.54 for (User *U : I.users())55 Next->insert(cast<Instruction>(U));56 I.replaceAllUsesWith(V);57 ++NumSimplified;58 Changed = true;59 // A call can get simplified, but it may not be trivially dead.60 if (isInstructionTriviallyDead(&I))61 DeadInstsInBB.push_back(&I);62 }63 }64 }65 RecursivelyDeleteTriviallyDeadInstructions(DeadInstsInBB, SQ.TLI);66 }67 68 // Place the list of instructions to simplify on the next loop iteration69 // into ToSimplify.70 std::swap(ToSimplify, Next);71 Next->clear();72 } while (!ToSimplify->empty());73 74 return Changed;75}76 77namespace {78struct InstSimplifyLegacyPass : public FunctionPass {79 static char ID; // Pass identification, replacement for typeid80 InstSimplifyLegacyPass() : FunctionPass(ID) {81 initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());82 }83 84 void getAnalysisUsage(AnalysisUsage &AU) const override {85 AU.setPreservesCFG();86 AU.addRequired<DominatorTreeWrapperPass>();87 AU.addRequired<AssumptionCacheTracker>();88 AU.addRequired<TargetLibraryInfoWrapperPass>();89 }90 91 /// Remove instructions that simplify.92 bool runOnFunction(Function &F) override {93 if (skipFunction(F))94 return false;95 96 const DominatorTree *DT =97 &getAnalysis<DominatorTreeWrapperPass>().getDomTree();98 const TargetLibraryInfo *TLI =99 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);100 AssumptionCache *AC =101 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);102 const DataLayout &DL = F.getDataLayout();103 const SimplifyQuery SQ(DL, TLI, DT, AC);104 return runImpl(F, SQ);105 }106};107} // namespace108 109char InstSimplifyLegacyPass::ID = 0;110INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",111 "Remove redundant instructions", false, false)112INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)113INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)114INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)115INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",116 "Remove redundant instructions", false, false)117 118// Public interface to the simplify instructions pass.119FunctionPass *llvm::createInstSimplifyLegacyPass() {120 return new InstSimplifyLegacyPass();121}122 123PreservedAnalyses InstSimplifyPass::run(Function &F,124 FunctionAnalysisManager &AM) {125 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);126 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);127 auto &AC = AM.getResult<AssumptionAnalysis>(F);128 const DataLayout &DL = F.getDataLayout();129 const SimplifyQuery SQ(DL, &TLI, &DT, &AC);130 bool Changed = runImpl(F, SQ);131 if (!Changed)132 return PreservedAnalyses::all();133 134 PreservedAnalyses PA;135 PA.preserveSet<CFGAnalyses>();136 return PA;137}138