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#include "llvm/Transforms/Scalar.h" 15#include "llvm/ADT/STLExtras.h" 16#include "llvm/ADT/Statistic.h" 17#include "llvm/Analysis/AssumptionCache.h" 18#include "llvm/Analysis/InstructionSimplify.h" 19#include "llvm/Analysis/LoopInfo.h" 20#include "llvm/Analysis/LoopPass.h" 21#include "llvm/Analysis/ScalarEvolution.h" 22#include "llvm/IR/DataLayout.h" 23#include "llvm/IR/Dominators.h" 24#include "llvm/IR/Instructions.h" 25#include "llvm/Support/Debug.h" 26#include "llvm/Analysis/TargetLibraryInfo.h" 27#include "llvm/Transforms/Utils/Local.h" 28#include "llvm/Transforms/Utils/LoopUtils.h" 29using namespace llvm; 30 31#define DEBUG_TYPE "loop-instsimplify" 32 33STATISTIC(NumSimplified, "Number of redundant instructions simplified"); 34 35namespace { 36 class LoopInstSimplify : public LoopPass { 37 public: 38 static char ID; // Pass ID, replacement for typeid 39 LoopInstSimplify() : LoopPass(ID) { 40 initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry()); 41 } 42 43 bool runOnLoop(Loop*, LPPassManager&) override; 44 45 void getAnalysisUsage(AnalysisUsage &AU) const override { 46 AU.addRequired<AssumptionCacheTracker>(); 47 AU.addRequired<TargetLibraryInfoWrapperPass>(); 48 AU.setPreservesCFG(); 49 getLoopAnalysisUsage(AU); 50 } 51 }; 52} 53 54char LoopInstSimplify::ID = 0; 55INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify", 56 "Simplify instructions in loops", false, false) 57INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 58INITIALIZE_PASS_DEPENDENCY(LoopPass) 59INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 60INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify", 61 "Simplify instructions in loops", false, false) 62 63Pass *llvm::createLoopInstSimplifyPass() { 64 return new LoopInstSimplify(); 65} 66 67bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 68 if (skipLoop(L)) 69 return false; 70 71 DominatorTreeWrapperPass *DTWP = 72 getAnalysisIfAvailable<DominatorTreeWrapperPass>(); 73 DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; 74 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 75 const TargetLibraryInfo *TLI = 76 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); 77 auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache( 78 *L->getHeader()->getParent()); 79 80 SmallVector<BasicBlock*, 8> ExitBlocks; 81 L->getUniqueExitBlocks(ExitBlocks); 82 array_pod_sort(ExitBlocks.begin(), ExitBlocks.end()); 83 84 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 85 86 // The bit we are stealing from the pointer represents whether this basic 87 // block is the header of a subloop, in which case we only process its phis. 88 typedef PointerIntPair<BasicBlock*, 1> WorklistItem; 89 SmallVector<WorklistItem, 16> VisitStack; 90 SmallPtrSet<BasicBlock*, 32> Visited; 91 92 bool Changed = false; 93 bool LocalChanged; 94 do { 95 LocalChanged = false; 96 97 VisitStack.clear(); 98 Visited.clear(); 99 100 VisitStack.push_back(WorklistItem(L->getHeader(), false)); 101 102 while (!VisitStack.empty()) { 103 WorklistItem Item = VisitStack.pop_back_val(); 104 BasicBlock *BB = Item.getPointer(); 105 bool IsSubloopHeader = Item.getInt(); 106 const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); 107 108 // Simplify instructions in the current basic block. 109 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { 110 Instruction *I = &*BI++; 111 112 // The first time through the loop ToSimplify is empty and we try to 113 // simplify all instructions. On later iterations ToSimplify is not 114 // empty and we only bother simplifying instructions that are in it. 115 if (!ToSimplify->empty() && !ToSimplify->count(I)) 116 continue; 117 118 // Don't bother simplifying unused instructions. 119 if (!I->use_empty()) { 120 Value *V = SimplifyInstruction(I, DL, TLI, DT, &AC); 121 if (V && LI->replacementPreservesLCSSAForm(I, V)) { 122 // Mark all uses for resimplification next time round the loop. 123 for (User *U : I->users()) 124 Next->insert(cast<Instruction>(U)); 125 126 I->replaceAllUsesWith(V); 127 LocalChanged = true; 128 ++NumSimplified; 129 } 130 } 131 if (RecursivelyDeleteTriviallyDeadInstructions(I, TLI)) { 132 // RecursivelyDeleteTriviallyDeadInstruction can remove more than one 133 // instruction, so simply incrementing the iterator does not work. 134 // When instructions get deleted re-iterate instead. 135 BI = BB->begin(); BE = BB->end(); 136 LocalChanged = true; 137 } 138 139 if (IsSubloopHeader && !isa<PHINode>(I)) 140 break; 141 } 142 143 // Add all successors to the worklist, except for loop exit blocks and the 144 // bodies of subloops. We visit the headers of loops so that we can process 145 // their phis, but we contract the rest of the subloop body and only follow 146 // edges leading back to the original loop. 147 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; 148 ++SI) { 149 BasicBlock *SuccBB = *SI; 150 if (!Visited.insert(SuccBB).second) 151 continue; 152 153 const Loop *SuccLoop = LI->getLoopFor(SuccBB); 154 if (SuccLoop && SuccLoop->getHeader() == SuccBB 155 && L->contains(SuccLoop)) { 156 VisitStack.push_back(WorklistItem(SuccBB, true)); 157 158 SmallVector<BasicBlock*, 8> SubLoopExitBlocks; 159 SuccLoop->getExitBlocks(SubLoopExitBlocks); 160 161 for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) { 162 BasicBlock *ExitBB = SubLoopExitBlocks[i]; 163 if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second) 164 VisitStack.push_back(WorklistItem(ExitBB, false)); 165 } 166 167 continue; 168 } 169 170 bool IsExitBlock = std::binary_search(ExitBlocks.begin(), 171 ExitBlocks.end(), SuccBB); 172 if (IsExitBlock) 173 continue; 174 175 VisitStack.push_back(WorklistItem(SuccBB, false)); 176 } 177 } 178 179 // Place the list of instructions to simplify on the next loop iteration 180 // into ToSimplify. 181 std::swap(ToSimplify, Next); 182 Next->clear(); 183 184 Changed |= LocalChanged; 185 } while (LocalChanged); 186 187 return Changed; 188} 189