contrib/llvm/lib/Transforms/Scalar/InstSimplifyPass.cpp

   1 //===- InstSimplifyPass.cpp -----------------------------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #include "llvm/Transforms/Scalar/InstSimplifyPass.h"
  11 #include "llvm/ADT/DepthFirstIterator.h"
  12 #include "llvm/ADT/SmallPtrSet.h"
  13 #include "llvm/ADT/Statistic.h"
  14 #include "llvm/Analysis/AssumptionCache.h"
  15 #include "llvm/Analysis/InstructionSimplify.h"
  16 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
  17 #include "llvm/Analysis/TargetLibraryInfo.h"
  18 #include "llvm/IR/DataLayout.h"
  19 #include "llvm/IR/Dominators.h"
  20 #include "llvm/IR/Function.h"
  21 #include "llvm/IR/Type.h"
  22 #include "llvm/Pass.h"
  23 #include "llvm/Transforms/Utils.h"
  24 #include "llvm/Transforms/Utils/Local.h"
  25 using namespace llvm;
  26
  27 #define DEBUG_TYPE "instsimplify"
  28
  29 STATISTIC(NumSimplified, "Number of redundant instructions removed");
  30
  31 static bool runImpl(Function &F, const SimplifyQuery &SQ,
  32                     OptimizationRemarkEmitter *ORE) {
  33   SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
  34   bool Changed = false;
  35
  36   do {
  37     for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
  38       // Here be subtlety: the iterator must be incremented before the loop
  39       // body (not sure why), so a range-for loop won't work here.
  40       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
  41         Instruction *I = &*BI++;
  42         // The first time through the loop ToSimplify is empty and we try to
  43         // simplify all instructions.  On later iterations ToSimplify is not
  44         // empty and we only bother simplifying instructions that are in it.
  45         if (!ToSimplify->empty() && !ToSimplify->count(I))
  46           continue;
  47
  48         // Don't waste time simplifying unused instructions.
  49         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           }
  58         }
  59         if (RecursivelyDeleteTriviallyDeadInstructions(I, SQ.TLI)) {
  60           // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
  61           // instruction, so simply incrementing the iterator does not work.
  62           // When instructions get deleted re-iterate instead.
  63           BI = BB->begin();
  64           BE = BB->end();
  65           Changed = true;
  66         }
  67       }
  68     }
  69
  70     // Place the list of instructions to simplify on the next loop iteration
  71     // into ToSimplify.
  72     std::swap(ToSimplify, Next);
  73     Next->clear();
  74   } while (!ToSimplify->empty());
  75
  76   return Changed;
  77 }
  78
  79 namespace {
  80 struct InstSimplifyLegacyPass : public FunctionPass {
  81   static char ID; // Pass identification, replacement for typeid
  82   InstSimplifyLegacyPass() : FunctionPass(ID) {
  83     initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
  84   }
  85
  86   void getAnalysisUsage(AnalysisUsage &AU) const override {
  87     AU.setPreservesCFG();
  88     AU.addRequired<DominatorTreeWrapperPass>();
  89     AU.addRequired<AssumptionCacheTracker>();
  90     AU.addRequired<TargetLibraryInfoWrapperPass>();
  91     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
  92   }
  93
  94   /// runOnFunction - Remove instructions that simplify.
  95   bool runOnFunction(Function &F) override {
  96     if (skipFunction(F))
  97       return false;
  98
  99     const DominatorTree *DT =
 100         &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 101     const TargetLibraryInfo *TLI =
 102         &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 103     AssumptionCache *AC =
 104         &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 105     OptimizationRemarkEmitter *ORE =
 106         &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
 107     const DataLayout &DL = F.getParent()->getDataLayout();
 108     const SimplifyQuery SQ(DL, TLI, DT, AC);
 109     return runImpl(F, SQ, ORE);
 110   }
 111 };
 112 } // namespace
 113
 114 char InstSimplifyLegacyPass::ID = 0;
 115 INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",
 116                       "Remove redundant instructions", false, false)
 117 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 118 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 119 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 120 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
 121 INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",
 122                     "Remove redundant instructions", false, false)
 123
 124 // Public interface to the simplify instructions pass.
 125 FunctionPass *llvm::createInstSimplifyLegacyPass() {
 126   return new InstSimplifyLegacyPass();
 127 }
 128
 129 PreservedAnalyses InstSimplifyPass::run(Function &F,
 130                                         FunctionAnalysisManager &AM) {
 131   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
 132   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
 133   auto &AC = AM.getResult<AssumptionAnalysis>(F);
 134   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
 135   const DataLayout &DL = F.getParent()->getDataLayout();
 136   const SimplifyQuery SQ(DL, &TLI, &DT, &AC);
 137   bool Changed = runImpl(F, SQ, &ORE);
 138   if (!Changed)
 139     return PreservedAnalyses::all();
 140
 141   PreservedAnalyses PA;
 142   PA.preserveSet<CFGAnalyses>();
 143   return PA;
 144 }