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