lib/Transforms/Scalar/LoopInstSimplify.cpp

   1 //===- LoopInstSimplify.cpp - Loop Instruction Simplification Pass --------===//
   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 pass performs lightweight instruction simplification on loop bodies.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #define DEBUG_TYPE "loop-instsimplify"
  15 #include "llvm/Function.h"
  16 #include "llvm/Pass.h"
  17 #include "llvm/Analysis/Dominators.h"
  18 #include "llvm/Analysis/InstructionSimplify.h"
  19 #include "llvm/Analysis/LoopInfo.h"
  20 #include "llvm/Target/TargetData.h"
  21 #include "llvm/Transforms/Scalar.h"
  22 #include "llvm/Transforms/Utils/Local.h"
  23 #include "llvm/ADT/Statistic.h"
  24 using namespace llvm;
  25
  26 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
  27
  28 namespace {
  29   class LoopInstSimplify : public FunctionPass {
  30   public:
  31     static char ID; // Pass ID, replacement for typeid
  32     LoopInstSimplify() : FunctionPass(ID) {
  33       initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
  34     }
  35
  36     bool runOnFunction(Function&);
  37
  38     virtual void getAnalysisUsage(AnalysisUsage& AU) const {
  39       AU.setPreservesCFG();
  40       AU.addRequired<LoopInfo>();
  41       AU.addPreserved<LoopInfo>();
  42       AU.addPreservedID(LCSSAID);
  43     }
  44   };
  45 }
  46
  47 char LoopInstSimplify::ID = 0;
  48 INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
  49                 "Simplify instructions in loops", false, false)
  50 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
  51 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
  52 INITIALIZE_PASS_DEPENDENCY(LCSSA)
  53 INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
  54                 "Simplify instructions in loops", false, false)
  55
  56 Pass* llvm::createLoopInstSimplifyPass() {
  57   return new LoopInstSimplify();
  58 }
  59
  60 bool LoopInstSimplify::runOnFunction(Function& F) {
  61   DominatorTree* DT = getAnalysisIfAvailable<DominatorTree>();
  62   LoopInfo* LI = &getAnalysis<LoopInfo>();
  63   const TargetData* TD = getAnalysisIfAvailable<TargetData>();
  64
  65   bool Changed = false;
  66   bool LocalChanged;
  67   do {
  68     LocalChanged = false;
  69
  70     for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
  71          DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
  72       for (BasicBlock::iterator BI = DI->begin(), BE = DI->end(); BI != BE;) {
  73         Instruction* I = BI++;
  74         // Don't bother simplifying unused instructions.
  75         if (!I->use_empty()) {
  76           Value* V = SimplifyInstruction(I, TD, DT);
  77           if (V && LI->replacementPreservesLCSSAForm(I, V)) {
  78             I->replaceAllUsesWith(V);
  79             LocalChanged = true;
  80             ++NumSimplified;
  81           }
  82         }
  83         LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
  84       }
  85
  86     Changed |= LocalChanged;
  87   } while (LocalChanged);
  88
  89   return Changed;
  90 }