llvm/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/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
  22 using namespace llvm;
  23
  24 #define DEBUG_TYPE "instsimplify"
  25
  26 STATISTIC(NumSimplified, "Number of redundant instructions removed");
  27
  28 static 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 to
  35       // 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 to
  42         // simplify all instructions. On later iterations, ToSimplify is not
  43         // 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 iteration
  69     // into ToSimplify.
  70     std::swap(ToSimplify, Next);
  71     Next->clear();
  72   } while (!ToSimplify->empty());
  73
  74   return Changed;
  75 }
  76
  77 namespace {
  78 struct InstSimplifyLegacyPass : public FunctionPass {
  79   static char ID; // Pass identification, replacement for typeid
  80   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 } // namespace
 108
 109 char InstSimplifyLegacyPass::ID = 0;
 110 INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",
 111                       "Remove redundant instructions", false, false)
 112 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 113 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 114 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 115 INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",
 116                     "Remove redundant instructions", false, false)
 117
 118 // Public interface to the simplify instructions pass.
 119 FunctionPass *llvm::createInstSimplifyLegacyPass() {
 120   return new InstSimplifyLegacyPass();
 121 }
 122
 123 PreservedAnalyses 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 }