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