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 } 113