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/Scalar.h"
  31 #include "llvm/Transforms/Utils/Local.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 = SimplifyInstruction(I, SQ, ORE)) {
  58             // Mark all uses for resimplification next time round the loop.
  59             for (User *U : I->users())
  60               Next->insert(cast<Instruction>(U));
  61             I->replaceAllUsesWith(V);
  62             ++NumSimplified;
  63             Changed = true;
  64           }
  65         }
  66         if (RecursivelyDeleteTriviallyDeadInstructions(I, SQ.TLI)) {
  67           // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
  68           // instruction, so simply incrementing the iterator does not work.
  69           // When instructions get deleted re-iterate instead.
  70           BI = BB->begin();
  71           BE = BB->end();
  72           Changed = true;
  73         }
  74       }
  75     }
  76
  77     // Place the list of instructions to simplify on the next loop iteration
  78     // into ToSimplify.
  79     std::swap(ToSimplify, Next);
  80     Next->clear();
  81   } while (!ToSimplify->empty());
  82
  83   return Changed;
  84 }
  85
  86 namespace {
  87   struct InstSimplifier : public FunctionPass {
  88     static char ID; // Pass identification, replacement for typeid
  89     InstSimplifier() : FunctionPass(ID) {
  90       initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
  91     }
  92
  93     void getAnalysisUsage(AnalysisUsage &AU) const override {
  94       AU.setPreservesCFG();
  95       AU.addRequired<DominatorTreeWrapperPass>();
  96       AU.addRequired<AssumptionCacheTracker>();
  97       AU.addRequired<TargetLibraryInfoWrapperPass>();
  98       AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
  99     }
 100
 101     /// runOnFunction - Remove instructions that simplify.
 102     bool runOnFunction(Function &F) override {
 103       if (skipFunction(F))
 104         return false;
 105
 106       const DominatorTree *DT =
 107           &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 108       const TargetLibraryInfo *TLI =
 109           &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
 110       AssumptionCache *AC =
 111           &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 112       OptimizationRemarkEmitter *ORE =
 113           &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
 114       const DataLayout &DL = F.getParent()->getDataLayout();
 115       const SimplifyQuery SQ(DL, TLI, DT, AC);
 116       return runImpl(F, SQ, ORE);
 117     }
 118   };
 119 }
 120
 121 char InstSimplifier::ID = 0;
 122 INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify",
 123                       "Remove redundant instructions", false, false)
 124 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 125 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 126 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 127 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
 128 INITIALIZE_PASS_END(InstSimplifier, "instsimplify",
 129                     "Remove redundant instructions", false, false)
 130 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
 131
 132 // Public interface to the simplify instructions pass.
 133 FunctionPass *llvm::createInstructionSimplifierPass() {
 134   return new InstSimplifier();
 135 }
 136
 137 PreservedAnalyses InstSimplifierPass::run(Function &F,
 138                                       FunctionAnalysisManager &AM) {
 139   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
 140   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
 141   auto &AC = AM.getResult<AssumptionAnalysis>(F);
 142   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
 143   const DataLayout &DL = F.getParent()->getDataLayout();
 144   const SimplifyQuery SQ(DL, &TLI, &DT, &AC);
 145   bool Changed = runImpl(F, SQ, &ORE);
 146   if (!Changed)
 147     return PreservedAnalyses::all();
 148
 149   PreservedAnalyses PA;
 150   PA.preserveSet<CFGAnalyses>();
 151   return PA;
 152 }