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/Analysis/Dominators.h"
  16 #include "llvm/Analysis/InstructionSimplify.h"
  17 #include "llvm/Analysis/LoopInfo.h"
  18 #include "llvm/Analysis/LoopPass.h"
  19 #include "llvm/Support/Debug.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 LoopPass {
  30   public:
  31     static char ID; // Pass ID, replacement for typeid
  32     LoopInstSimplify() : LoopPass(ID) {
  33       initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
  34     }
  35
  36     bool runOnLoop(Loop*, LPPassManager&);
  37
  38     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  39       AU.setPreservesCFG();
  40       AU.addRequired<LoopInfo>();
  41       AU.addRequiredID(LoopSimplifyID);
  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::runOnLoop(Loop *L, LPPassManager &LPM) {
  61   DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
  62   LoopInfo *LI = &getAnalysis<LoopInfo>();
  63   const TargetData *TD = getAnalysisIfAvailable<TargetData>();
  64
  65   SmallVector<BasicBlock*, 8> ExitBlocks;
  66   L->getUniqueExitBlocks(ExitBlocks);
  67   array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
  68
  69   SmallVector<BasicBlock*, 16> VisitStack;
  70   SmallPtrSet<BasicBlock*, 32> Visited;
  71
  72   bool Changed = false;
  73   bool LocalChanged;
  74   do {
  75     LocalChanged = false;
  76
  77     VisitStack.clear();
  78     Visited.clear();
  79
  80     VisitStack.push_back(L->getHeader());
  81
  82     while (!VisitStack.empty()) {
  83       BasicBlock *BB = VisitStack.back();
  84       VisitStack.pop_back();
  85
  86       // Simplify instructions in the current basic block.
  87       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
  88         Instruction *I = BI++;
  89         // Don't bother simplifying unused instructions.
  90         if (!I->use_empty()) {
  91           Value *V = SimplifyInstruction(I, TD, DT);
  92           if (V && LI->replacementPreservesLCSSAForm(I, V)) {
  93             I->replaceAllUsesWith(V);
  94             LocalChanged = true;
  95             ++NumSimplified;
  96           }
  97         }
  98         LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
  99       }
 100
 101       // Add all successors to the worklist, except for loop exit blocks.
 102       for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
 103            ++SI) {
 104         BasicBlock *SuccBB = *SI;
 105         bool IsExitBlock = std::binary_search(ExitBlocks.begin(),
 106                                              ExitBlocks.end(), SuccBB);
 107         if (!IsExitBlock && Visited.insert(SuccBB))
 108           VisitStack.push_back(SuccBB);
 109       }
 110     }
 111
 112     Changed |= LocalChanged;
 113   } while (LocalChanged);
 114
 115   return Changed;
 116 }