contrib/llvm/lib/Transforms/Utils/SimplifyInstructions.cpp

   1 //===------ SimplifyInstructions.cpp - Remove redundant instructions ------===//
   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 // This is a utility pass used for testing the InstructionSimplify analysis.
  11 // The analysis is applied to every instruction, and if it simplifies then the
  12 // instruction is replaced by the simplification.  If you are looking for a pass
  13 // that performs serious instruction folding, use the instcombine pass instead.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "llvm/Transforms/Utils/SimplifyInstructions.h"
  18 #include "llvm/ADT/DepthFirstIterator.h"
  19 #include "llvm/ADT/SmallPtrSet.h"
  20 #include "llvm/ADT/Statistic.h"
  21 #include "llvm/Analysis/AssumptionCache.h"
  22 #include "llvm/Analysis/InstructionSimplify.h"
  23 #include "llvm/Analysis/OptimizationDiagnosticInfo.h"
  24 #include "llvm/Analysis/TargetLibraryInfo.h"
  25 #include "llvm/IR/DataLayout.h"
  26 #include "llvm/IR/Dominators.h"
  27 #include "llvm/IR/Function.h"
  28 #include "llvm/IR/Type.h"
  29 #include "llvm/Pass.h"
  30 #include "llvm/Transforms/Utils/Local.h"
  31 #include "llvm/Transforms/Scalar.h"
  32 using namespace llvm;
  33
  34 #define DEBUG_TYPE "instsimplify"
  35
  36 STATISTIC(NumSimplified, "Number of redundant instructions removed");
  37
  38 static bool runImpl(Function &F, const SimplifyQuery &SQ,
  39                     OptimizationRemarkEmitter *ORE) {
  40   SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
  41   bool Changed = false;
  42
  43   do {
  44     for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
  45       // Here be subtlety: the iterator must be incremented before the loop
  46       // body (not sure why), so a range-for loop won't work here.
  47       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
  48         Instruction *I = &*BI++;
  49         // The first time through the loop ToSimplify is empty and we try to
  50         // simplify all instructions.  On later iterations ToSimplify is not
  51         // empty and we only bother simplifying instructions that are in it.
  52         if (!ToSimplify->empty() && !ToSimplify->count(I))
  53           continue;
  54
  55         // Don't waste time simplifying unused instructions.
  56         if (!I->use_empty()) {
  57           if (Value *V =
  58                   SimplifyInstruction(I, SQ.getWithInstruction(I), ORE)) {
  59             // Mark all uses for resimplification next time round the loop.
  60             for (User *U : I->users())
  61               Next->insert(cast<Instruction>(U));
  62             I->replaceAllUsesWith(V);
  63             ++NumSimplified;
  64             Changed = true;
  65           }
  66         }
  67         if (RecursivelyDeleteTriviallyDeadInstructions(I, SQ.TLI)) {
  68           // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
  69           // instruction, so simply incrementing the iterator does not work.
  70           // When instructions get deleted re-iterate instead.
  71           BI = BB->begin();
  72           BE = BB->end();
  73           Changed = true;
  74         }
  75       }
  76     }
  77
  78     // Place the list of instructions to simplify on the next loop iteration
  79     // into ToSimplify.
  80     std::swap(ToSimplify, Next);
  81     Next->clear();
  82   } while (!ToSimplify->empty());
  83
  84   return Changed;
  85 }
  86
  87 namespace {
  88   struct InstSimplifier : public FunctionPass {
  89     static char ID; // Pass identification, replacement for typeid
  90     InstSimplifier() : FunctionPass(ID) {
  91       initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
  92     }
  93
  94     void getAnalysisUsage(AnalysisUsage &AU) const override {
  95       AU.setPreservesCFG();
  96       AU.addRequired<DominatorTreeWrapperPass>();
  97       AU.addRequired<AssumptionCacheTracker>();
  98       AU.addRequired<TargetLibraryInfoWrapperPass>();
  99       AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
 100     }
 101
 102     /// runOnFunction - Remove instructions that simplify.
 103     bool runOnFunction(Function &F) override {
 104       if (skipFunction(F))
 105         return false;
 106
 107       const DominatorTree *DT =
 108           &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 109       const TargetLibraryInfo *TLI =
 110           &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 111       AssumptionCache *AC =
 112           &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 113       OptimizationRemarkEmitter *ORE =
 114           &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
 115       const DataLayout &DL = F.getParent()->getDataLayout();
 116       const SimplifyQuery SQ(DL, TLI, DT, AC);
 117       return runImpl(F, SQ, ORE);
 118     }
 119   };
 120 }
 121
 122 char InstSimplifier::ID = 0;
 123 INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify",
 124                       "Remove redundant instructions", false, false)
 125 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 126 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 127 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 128 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
 129 INITIALIZE_PASS_END(InstSimplifier, "instsimplify",
 130                     "Remove redundant instructions", false, false)
 131 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
 132
 133 // Public interface to the simplify instructions pass.
 134 FunctionPass *llvm::createInstructionSimplifierPass() {
 135   return new InstSimplifier();
 136 }
 137
 138 PreservedAnalyses InstSimplifierPass::run(Function &F,
 139                                       FunctionAnalysisManager &AM) {
 140   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
 141   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
 142   auto &AC = AM.getResult<AssumptionAnalysis>(F);
 143   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
 144   const DataLayout &DL = F.getParent()->getDataLayout();
 145   const SimplifyQuery SQ(DL, &TLI, &DT, &AC);
 146   bool Changed = runImpl(F, SQ, &ORE);
 147   if (!Changed)
 148     return PreservedAnalyses::all();
 149
 150   PreservedAnalyses PA;
 151   PA.preserveSet<CFGAnalyses>();
 152   return PA;
 153 }