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/LoopInstSimplify.h" 15 #include "llvm/ADT/PointerIntPair.h" 16 #include "llvm/ADT/STLExtras.h" 17 #include "llvm/ADT/SmallPtrSet.h" 18 #include "llvm/ADT/SmallVector.h" 19 #include "llvm/ADT/Statistic.h" 20 #include "llvm/Analysis/AssumptionCache.h" 21 #include "llvm/Analysis/InstructionSimplify.h" 22 #include "llvm/Analysis/LoopInfo.h" 23 #include "llvm/Analysis/LoopPass.h" 24 #include "llvm/Analysis/TargetLibraryInfo.h" 25 #include "llvm/Analysis/Utils/Local.h" 26 #include "llvm/IR/BasicBlock.h" 27 #include "llvm/IR/CFG.h" 28 #include "llvm/IR/DataLayout.h" 29 #include "llvm/IR/Dominators.h" 30 #include "llvm/IR/Instruction.h" 31 #include "llvm/IR/Instructions.h" 32 #include "llvm/IR/Module.h" 33 #include "llvm/IR/PassManager.h" 34 #include "llvm/IR/User.h" 35 #include "llvm/Pass.h" 36 #include "llvm/Support/Casting.h" 37 #include "llvm/Transforms/Scalar.h" 38 #include "llvm/Transforms/Utils/LoopUtils.h" 39 #include <algorithm> 40 #include <utility> 41 42 using namespace llvm; 43 44 #define DEBUG_TYPE "loop-instsimplify" 45 46 STATISTIC(NumSimplified, "Number of redundant instructions simplified"); 47 48 static bool SimplifyLoopInst(Loop *L, DominatorTree *DT, LoopInfo *LI, 49 AssumptionCache *AC, 50 const TargetLibraryInfo *TLI) { 51 SmallVector<BasicBlock *, 8> ExitBlocks; 52 L->getUniqueExitBlocks(ExitBlocks); 53 array_pod_sort(ExitBlocks.begin(), ExitBlocks.end()); 54 55 SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 56 57 // The bit we are stealing from the pointer represents whether this basic 58 // block is the header of a subloop, in which case we only process its phis. 59 using WorklistItem = PointerIntPair<BasicBlock *, 1>; 60 SmallVector<WorklistItem, 16> VisitStack; 61 SmallPtrSet<BasicBlock *, 32> Visited; 62 63 bool Changed = false; 64 bool LocalChanged; 65 do { 66 LocalChanged = false; 67 68 VisitStack.clear(); 69 Visited.clear(); 70 71 VisitStack.push_back(WorklistItem(L->getHeader(), false)); 72 73 while (!VisitStack.empty()) { 74 WorklistItem Item = VisitStack.pop_back_val(); 75 BasicBlock *BB = Item.getPointer(); 76 bool IsSubloopHeader = Item.getInt(); 77 const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); 78 79 // Simplify instructions in the current basic block. 80 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { 81 Instruction *I = &*BI++; 82 83 // The first time through the loop ToSimplify is empty and we try to 84 // simplify all instructions. On later iterations ToSimplify is not 85 // empty and we only bother simplifying instructions that are in it. 86 if (!ToSimplify->empty() && !ToSimplify->count(I)) 87 continue; 88 89 // Don't bother simplifying unused instructions. 90 if (!I->use_empty()) { 91 Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC}); 92 if (V && LI->replacementPreservesLCSSAForm(I, V)) { 93 // Mark all uses for resimplification next time round the loop. 94 for (User *U : I->users()) 95 Next->insert(cast<Instruction>(U)); 96 97 I->replaceAllUsesWith(V); 98 LocalChanged = true; 99 ++NumSimplified; 100 } 101 } 102 if (RecursivelyDeleteTriviallyDeadInstructions(I, TLI)) { 103 // RecursivelyDeleteTriviallyDeadInstruction can remove more than one 104 // instruction, so simply incrementing the iterator does not work. 105 // When instructions get deleted re-iterate instead. 106 BI = BB->begin(); 107 BE = BB->end(); 108 LocalChanged = true; 109 } 110 111 if (IsSubloopHeader && !isa<PHINode>(I)) 112 break; 113 } 114 115 // Add all successors to the worklist, except for loop exit blocks and the 116 // bodies of subloops. We visit the headers of loops so that we can 117 // process 118 // their phis, but we contract the rest of the subloop body and only 119 // follow 120 // edges leading back to the original loop. 121 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; 122 ++SI) { 123 BasicBlock *SuccBB = *SI; 124 if (!Visited.insert(SuccBB).second) 125 continue; 126 127 const Loop *SuccLoop = LI->getLoopFor(SuccBB); 128 if (SuccLoop && SuccLoop->getHeader() == SuccBB && 129 L->contains(SuccLoop)) { 130 VisitStack.push_back(WorklistItem(SuccBB, true)); 131 132 SmallVector<BasicBlock *, 8> SubLoopExitBlocks; 133 SuccLoop->getExitBlocks(SubLoopExitBlocks); 134 135 for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) { 136 BasicBlock *ExitBB = SubLoopExitBlocks[i]; 137 if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second) 138 VisitStack.push_back(WorklistItem(ExitBB, false)); 139 } 140 141 continue; 142 } 143 144 bool IsExitBlock = 145 std::binary_search(ExitBlocks.begin(), ExitBlocks.end(), SuccBB); 146 if (IsExitBlock) 147 continue; 148 149 VisitStack.push_back(WorklistItem(SuccBB, false)); 150 } 151 } 152 153 // Place the list of instructions to simplify on the next loop iteration 154 // into ToSimplify. 155 std::swap(ToSimplify, Next); 156 Next->clear(); 157 158 Changed |= LocalChanged; 159 } while (LocalChanged); 160 161 return Changed; 162 } 163 164 namespace { 165 166 class LoopInstSimplifyLegacyPass : public LoopPass { 167 public: 168 static char ID; // Pass ID, replacement for typeid 169 170 LoopInstSimplifyLegacyPass() : LoopPass(ID) { 171 initializeLoopInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry()); 172 } 173 174 bool runOnLoop(Loop *L, LPPassManager &LPM) override { 175 if (skipLoop(L)) 176 return false; 177 DominatorTreeWrapperPass *DTWP = 178 getAnalysisIfAvailable<DominatorTreeWrapperPass>(); 179 DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; 180 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 181 AssumptionCache *AC = 182 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache( 183 *L->getHeader()->getParent()); 184 const TargetLibraryInfo *TLI = 185 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); 186 187 return SimplifyLoopInst(L, DT, LI, AC, TLI); 188 } 189 190 void getAnalysisUsage(AnalysisUsage &AU) const override { 191 AU.addRequired<AssumptionCacheTracker>(); 192 AU.addRequired<TargetLibraryInfoWrapperPass>(); 193 AU.setPreservesCFG(); 194 getLoopAnalysisUsage(AU); 195 } 196 }; 197 198 } // end anonymous namespace 199 200 PreservedAnalyses LoopInstSimplifyPass::run(Loop &L, LoopAnalysisManager &AM, 201 LoopStandardAnalysisResults &AR, 202 LPMUpdater &) { 203 if (!SimplifyLoopInst(&L, &AR.DT, &AR.LI, &AR.AC, &AR.TLI)) 204 return PreservedAnalyses::all(); 205 206 auto PA = getLoopPassPreservedAnalyses(); 207 PA.preserveSet<CFGAnalyses>(); 208 return PA; 209 } 210 211 char LoopInstSimplifyLegacyPass::ID = 0; 212 213 INITIALIZE_PASS_BEGIN(LoopInstSimplifyLegacyPass, "loop-instsimplify", 214 "Simplify instructions in loops", false, false) 215 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 216 INITIALIZE_PASS_DEPENDENCY(LoopPass) 217 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 218 INITIALIZE_PASS_END(LoopInstSimplifyLegacyPass, "loop-instsimplify", 219 "Simplify instructions in loops", false, false) 220 221 Pass *llvm::createLoopInstSimplifyPass() { 222 return new LoopInstSimplifyLegacyPass(); 223 } 224