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 : depth_first(&F.getEntryBlock())) {
  37       // Here be subtlety: the iterator must be incremented before the loop
  38       // body (not sure why), so a range-for loop won't work here.
  39       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
  40         Instruction *I = &*BI++;
  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 unused instructions.
  48         if (!I->use_empty()) {
  49           if (Value *V = SimplifyInstruction(I, SQ, ORE)) {
  50             // Mark all uses for resimplification next time round the loop.
  51             for (User *U : I->users())
  52               Next->insert(cast<Instruction>(U));
  53             I->replaceAllUsesWith(V);
  54             ++NumSimplified;
  55             Changed = true;
  56           }
  57         }
  58         if (RecursivelyDeleteTriviallyDeadInstructions(I, SQ.TLI)) {
  59           // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
  60           // instruction, so simply incrementing the iterator does not work.
  61           // When instructions get deleted re-iterate instead.
  62           BI = BB->begin();
  63           BE = BB->end();
  64           Changed = true;
  65         }
  66       }
  67     }
  68
  69     // Place the list of instructions to simplify on the next loop iteration
  70     // into ToSimplify.
  71     std::swap(ToSimplify, Next);
  72     Next->clear();
  73   } while (!ToSimplify->empty());
  74
  75   return Changed;
  76 }
  77
  78 namespace {
  79 struct InstSimplifyLegacyPass : public FunctionPass {
  80   static char ID; // Pass identification, replacement for typeid
  81   InstSimplifyLegacyPass() : FunctionPass(ID) {
  82     initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
  83   }
  84
  85   void getAnalysisUsage(AnalysisUsage &AU) const override {
  86     AU.setPreservesCFG();
  87     AU.addRequired<DominatorTreeWrapperPass>();
  88     AU.addRequired<AssumptionCacheTracker>();
  89     AU.addRequired<TargetLibraryInfoWrapperPass>();
  90     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
  91   }
  92
  93   /// runOnFunction - Remove instructions that simplify.
  94   bool runOnFunction(Function &F) override {
  95     if (skipFunction(F))
  96       return false;
  97
  98     const DominatorTree *DT =
  99         &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 100     const TargetLibraryInfo *TLI =
 101         &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 102     AssumptionCache *AC =
 103         &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 104     OptimizationRemarkEmitter *ORE =
 105         &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
 106     const DataLayout &DL = F.getParent()->getDataLayout();
 107     const SimplifyQuery SQ(DL, TLI, DT, AC);
 108     return runImpl(F, SQ, ORE);
 109   }
 110 };
 111 } // namespace
 112
 113 char InstSimplifyLegacyPass::ID = 0;
 114 INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",
 115                       "Remove redundant instructions", false, false)
 116 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 117 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 118 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 119 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
 120 INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",
 121                     "Remove redundant instructions", false, false)
 122
 123 // Public interface to the simplify instructions pass.
 124 FunctionPass *llvm::createInstSimplifyLegacyPass() {
 125   return new InstSimplifyLegacyPass();
 126 }
 127
 128 PreservedAnalyses InstSimplifyPass::run(Function &F,
 129                                         FunctionAnalysisManager &AM) {
 130   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
 131   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
 132   auto &AC = AM.getResult<AssumptionAnalysis>(F);
 133   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
 134   const DataLayout &DL = F.getParent()->getDataLayout();
 135   const SimplifyQuery SQ(DL, &TLI, &DT, &AC);
 136   bool Changed = runImpl(F, SQ, &ORE);
 137   if (!Changed)
 138     return PreservedAnalyses::all();
 139
 140   PreservedAnalyses PA;
 141   PA.preserveSet<CFGAnalyses>();
 142   return PA;
 143 }