1 //===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements Loop Rotation Pass. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/Transforms/Scalar/LoopRotation.h" 14 #include "llvm/Analysis/AssumptionCache.h" 15 #include "llvm/Analysis/InstructionSimplify.h" 16 #include "llvm/Analysis/LazyBlockFrequencyInfo.h" 17 #include "llvm/Analysis/LoopInfo.h" 18 #include "llvm/Analysis/LoopPass.h" 19 #include "llvm/Analysis/MemorySSA.h" 20 #include "llvm/Analysis/MemorySSAUpdater.h" 21 #include "llvm/Analysis/ScalarEvolution.h" 22 #include "llvm/Analysis/TargetTransformInfo.h" 23 #include "llvm/InitializePasses.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Transforms/Scalar.h" 26 #include "llvm/Transforms/Utils/LoopRotationUtils.h" 27 #include "llvm/Transforms/Utils/LoopUtils.h" 28 using namespace llvm; 29 30 #define DEBUG_TYPE "loop-rotate" 31 32 static cl::opt<unsigned> DefaultRotationThreshold( 33 "rotation-max-header-size", cl::init(16), cl::Hidden, 34 cl::desc("The default maximum header size for automatic loop rotation")); 35 36 static cl::opt<bool> PrepareForLTOOption( 37 "rotation-prepare-for-lto", cl::init(false), cl::Hidden, 38 cl::desc("Run loop-rotation in the prepare-for-lto stage. This option " 39 "should be used for testing only.")); 40 41 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO) 42 : EnableHeaderDuplication(EnableHeaderDuplication), 43 PrepareForLTO(PrepareForLTO) {} 44 45 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM, 46 LoopStandardAnalysisResults &AR, 47 LPMUpdater &) { 48 // Vectorization requires loop-rotation. Use default threshold for loops the 49 // user explicitly marked for vectorization, even when header duplication is 50 // disabled. 51 int Threshold = EnableHeaderDuplication || 52 hasVectorizeTransformation(&L) == TM_ForcedByUser 53 ? DefaultRotationThreshold 54 : 0; 55 const DataLayout &DL = L.getHeader()->getModule()->getDataLayout(); 56 const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL); 57 58 Optional<MemorySSAUpdater> MSSAU; 59 if (AR.MSSA) 60 MSSAU = MemorySSAUpdater(AR.MSSA); 61 bool Changed = 62 LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE, 63 MSSAU ? MSSAU.getPointer() : nullptr, SQ, false, Threshold, 64 false, PrepareForLTO || PrepareForLTOOption); 65 66 if (!Changed) 67 return PreservedAnalyses::all(); 68 69 if (AR.MSSA && VerifyMemorySSA) 70 AR.MSSA->verifyMemorySSA(); 71 72 auto PA = getLoopPassPreservedAnalyses(); 73 if (AR.MSSA) 74 PA.preserve<MemorySSAAnalysis>(); 75 return PA; 76 } 77 78 namespace { 79 80 class LoopRotateLegacyPass : public LoopPass { 81 unsigned MaxHeaderSize; 82 bool PrepareForLTO; 83 84 public: 85 static char ID; // Pass ID, replacement for typeid 86 LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1, 87 bool PrepareForLTO = false) 88 : LoopPass(ID), PrepareForLTO(PrepareForLTO) { 89 initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry()); 90 if (SpecifiedMaxHeaderSize == -1) 91 MaxHeaderSize = DefaultRotationThreshold; 92 else 93 MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize); 94 } 95 96 // LCSSA form makes instruction renaming easier. 97 void getAnalysisUsage(AnalysisUsage &AU) const override { 98 AU.addRequired<AssumptionCacheTracker>(); 99 AU.addRequired<TargetTransformInfoWrapperPass>(); 100 AU.addPreserved<MemorySSAWrapperPass>(); 101 getLoopAnalysisUsage(AU); 102 103 // Lazy BFI and BPI are marked as preserved here so LoopRotate 104 // can remain part of the same loop pass manager as LICM. 105 AU.addPreserved<LazyBlockFrequencyInfoPass>(); 106 AU.addPreserved<LazyBranchProbabilityInfoPass>(); 107 } 108 109 bool runOnLoop(Loop *L, LPPassManager &LPM) override { 110 if (skipLoop(L)) 111 return false; 112 Function &F = *L->getHeader()->getParent(); 113 114 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 115 const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); 116 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); 117 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 118 auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE(); 119 const SimplifyQuery SQ = getBestSimplifyQuery(*this, F); 120 Optional<MemorySSAUpdater> MSSAU; 121 // Not requiring MemorySSA and getting it only if available will split 122 // the loop pass pipeline when LoopRotate is being run first. 123 auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>(); 124 if (MSSAA) 125 MSSAU = MemorySSAUpdater(&MSSAA->getMSSA()); 126 // Vectorization requires loop-rotation. Use default threshold for loops the 127 // user explicitly marked for vectorization, even when header duplication is 128 // disabled. 129 int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser 130 ? DefaultRotationThreshold 131 : MaxHeaderSize; 132 133 return LoopRotation(L, LI, TTI, AC, &DT, &SE, 134 MSSAU ? MSSAU.getPointer() : nullptr, SQ, false, 135 Threshold, false, PrepareForLTO || PrepareForLTOOption); 136 } 137 }; 138 } // end namespace 139 140 char LoopRotateLegacyPass::ID = 0; 141 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", 142 false, false) 143 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 144 INITIALIZE_PASS_DEPENDENCY(LoopPass) 145 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) 146 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass) 147 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false, 148 false) 149 150 Pass *llvm::createLoopRotatePass(int MaxHeaderSize, bool PrepareForLTO) { 151 return new LoopRotateLegacyPass(MaxHeaderSize, PrepareForLTO); 152 } 153