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/Instructions.h" 16#include "llvm/Analysis/Dominators.h" 17#include "llvm/Analysis/InstructionSimplify.h" 18#include "llvm/Analysis/LoopInfo.h" 19#include "llvm/Analysis/LoopPass.h" 20#include "llvm/Support/Debug.h" 21#include "llvm/Target/TargetData.h" 22#include "llvm/Transforms/Scalar.h" 23#include "llvm/Transforms/Utils/Local.h" 24#include "llvm/ADT/Statistic.h" 25using namespace llvm; 26 27STATISTIC(NumSimplified, "Number of redundant instructions simplified"); 28 29namespace { 30 class LoopInstSimplify : public LoopPass { 31 public: 32 static char ID; // Pass ID, replacement for typeid 33 LoopInstSimplify() : LoopPass(ID) { 34 initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry()); 35 } 36 37 bool runOnLoop(Loop*, LPPassManager&); 38 39 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 40 AU.setPreservesCFG(); 41 AU.addRequired<LoopInfo>(); 42 AU.addRequiredID(LoopSimplifyID); 43 AU.addPreservedID(LoopSimplifyID); 44 AU.addPreservedID(LCSSAID); 45 AU.addPreserved("scalar-evolution"); 46 } 47 }; 48} 49 50char LoopInstSimplify::ID = 0; 51INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify", 52 "Simplify instructions in loops", false, false) 53INITIALIZE_PASS_DEPENDENCY(DominatorTree) 54INITIALIZE_PASS_DEPENDENCY(LoopInfo) 55INITIALIZE_PASS_DEPENDENCY(LCSSA) 56INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify", 57 "Simplify instructions in loops", false, false) 58 59Pass *llvm::createLoopInstSimplifyPass() { 60 return new LoopInstSimplify(); 61} 62 63bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 64 DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>(); 65 LoopInfo *LI = &getAnalysis<LoopInfo>(); 66 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 67 68 SmallVector<BasicBlock*, 8> ExitBlocks; 69 L->getUniqueExitBlocks(ExitBlocks); 70 array_pod_sort(ExitBlocks.begin(), ExitBlocks.end()); 71 72 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 73 74 // The bit we are stealing from the pointer represents whether this basic 75 // block is the header of a subloop, in which case we only process its phis. 76 typedef PointerIntPair<BasicBlock*, 1> WorklistItem; 77 SmallVector<WorklistItem, 16> VisitStack; 78 SmallPtrSet<BasicBlock*, 32> Visited; 79 80 bool Changed = false; 81 bool LocalChanged; 82 do { 83 LocalChanged = false; 84 85 VisitStack.clear(); 86 Visited.clear(); 87 88 VisitStack.push_back(WorklistItem(L->getHeader(), false)); 89 90 while (!VisitStack.empty()) { 91 WorklistItem Item = VisitStack.pop_back_val(); 92 BasicBlock *BB = Item.getPointer(); 93 bool IsSubloopHeader = Item.getInt(); 94 95 // Simplify instructions in the current basic block. 96 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { 97 Instruction *I = BI++; 98 99 // The first time through the loop ToSimplify is empty and we try to 100 // simplify all instructions. On later iterations ToSimplify is not 101 // empty and we only bother simplifying instructions that are in it. 102 if (!ToSimplify->empty() && !ToSimplify->count(I)) 103 continue; 104 105 // Don't bother simplifying unused instructions. 106 if (!I->use_empty()) { 107 Value *V = SimplifyInstruction(I, TD, DT); 108 if (V && LI->replacementPreservesLCSSAForm(I, V)) { 109 // Mark all uses for resimplification next time round the loop. 110 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 111 UI != UE; ++UI) 112 Next->insert(cast<Instruction>(*UI)); 113 114 I->replaceAllUsesWith(V); 115 LocalChanged = true; 116 ++NumSimplified; 117 } 118 } 119 LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I); 120 121 if (IsSubloopHeader && !isa<PHINode>(I)) 122 break; 123 } 124 125 // Add all successors to the worklist, except for loop exit blocks and the 126 // bodies of subloops. We visit the headers of loops so that we can process 127 // their phis, but we contract the rest of the subloop body and only follow 128 // edges leading back to the original loop. 129 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; 130 ++SI) { 131 BasicBlock *SuccBB = *SI; 132 if (!Visited.insert(SuccBB)) 133 continue; 134 135 const Loop *SuccLoop = LI->getLoopFor(SuccBB); 136 if (SuccLoop && SuccLoop->getHeader() == SuccBB 137 && L->contains(SuccLoop)) { 138 VisitStack.push_back(WorklistItem(SuccBB, true)); 139 140 SmallVector<BasicBlock*, 8> SubLoopExitBlocks; 141 SuccLoop->getExitBlocks(SubLoopExitBlocks); 142 143 for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) { 144 BasicBlock *ExitBB = SubLoopExitBlocks[i]; 145 if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB)) 146 VisitStack.push_back(WorklistItem(ExitBB, false)); 147 } 148 149 continue; 150 } 151 152 bool IsExitBlock = std::binary_search(ExitBlocks.begin(), 153 ExitBlocks.end(), SuccBB); 154 if (IsExitBlock) 155 continue; 156 157 VisitStack.push_back(WorklistItem(SuccBB, false)); 158 } 159 } 160 161 // Place the list of instructions to simplify on the next loop iteration 162 // into ToSimplify. 163 std::swap(ToSimplify, Next); 164 Next->clear(); 165 166 Changed |= LocalChanged; 167 } while (LocalChanged); 168 169 return Changed; 170} 171