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/LoopPass.h"
  16 #include "llvm/Analysis/Dominators.h"
  17 #include "llvm/Analysis/InstructionSimplify.h"
  18 #include "llvm/Target/TargetData.h"
  19 #include "llvm/Transforms/Scalar.h"
  20 #include "llvm/Transforms/Utils/Local.h"
  21 #include "llvm/ADT/Statistic.h"
  22 using namespace llvm;
  23
  24 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
  25
  26 namespace {
  27   class LoopInstSimplify : public LoopPass {
  28   public:
  29     static char ID; // Pass ID, replacement for typeid
  30     LoopInstSimplify() : LoopPass(ID) {
  31       initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
  32     }
  33
  34     bool runOnLoop(Loop*, LPPassManager&);
  35
  36     virtual void getAnalysisUsage(AnalysisUsage& AU) const {
  37       AU.setPreservesCFG();
  38       AU.addRequired<DominatorTree>();
  39       AU.addPreserved<DominatorTree>();
  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::runOnLoop(Loop* L, LPPassManager& LPM) {
  61   DominatorTree* DT = &getAnalysis<DominatorTree>();
  62   const 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     SmallPtrSet<BasicBlock*, 32> Visited;
  71     SmallVector<BasicBlock*, 32> VisitStack;
  72
  73     VisitStack.push_back(L->getHeader());
  74
  75     while (!VisitStack.empty()) {
  76       BasicBlock* BB = VisitStack.back();
  77       VisitStack.pop_back();
  78
  79       if (Visited.count(BB))
  80         continue;
  81       Visited.insert(BB);
  82
  83       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
  84         Instruction* I = BI++;
  85         // Don't bother simplifying unused instructions.
  86         if (!I->use_empty()) {
  87           if (Value* V = SimplifyInstruction(I, TD, DT)) {
  88             I->replaceAllUsesWith(V);
  89             LocalChanged = true;
  90             ++NumSimplified;
  91           }
  92         }
  93         LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
  94       }
  95       Changed |= LocalChanged;
  96
  97       DomTreeNode* Node = DT->getNode(BB);
  98       const std::vector<DomTreeNode*>& Children = Node->getChildren();
  99       for (unsigned i = 0; i < Children.size(); ++i) {
 100         // Only visit children that are in the same loop.
 101         BasicBlock* ChildBB = Children[i]->getBlock();
 102         if (!Visited.count(ChildBB) && LI->getLoopFor(ChildBB) == L)
 103           VisitStack.push_back(ChildBB);
 104       }
 105     }
 106   } while (LocalChanged);
 107
 108   // Nothing that SimplifyInstruction() does should invalidate LCSSA form.
 109   assert(L->isLCSSAForm(*DT));
 110
 111   return Changed;
 112 }