llvm/lib/Transforms/Scalar/LoopRotation.cpp

   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 #include <optional>
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "loop-rotate"
  32
  33 static cl::opt<unsigned> DefaultRotationThreshold(
  34     "rotation-max-header-size", cl::init(16), cl::Hidden,
  35     cl::desc("The default maximum header size for automatic loop rotation"));
  36
  37 static cl::opt<bool> PrepareForLTOOption(
  38     "rotation-prepare-for-lto", cl::init(false), cl::Hidden,
  39     cl::desc("Run loop-rotation in the prepare-for-lto stage. This option "
  40              "should be used for testing only."));
  41
  42 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO)
  43     : EnableHeaderDuplication(EnableHeaderDuplication),
  44       PrepareForLTO(PrepareForLTO) {}
  45
  46 void LoopRotatePass::printPipeline(
  47     raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
  48   static_cast<PassInfoMixin<LoopRotatePass> *>(this)->printPipeline(
  49       OS, MapClassName2PassName);
  50   OS << "<";
  51   if (!EnableHeaderDuplication)
  52     OS << "no-";
  53   OS << "header-duplication;";
  54
  55   if (!PrepareForLTO)
  56     OS << "no-";
  57   OS << "prepare-for-lto";
  58   OS << ">";
  59 }
  60
  61 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
  62                                       LoopStandardAnalysisResults &AR,
  63                                       LPMUpdater &) {
  64   // Vectorization requires loop-rotation. Use default threshold for loops the
  65   // user explicitly marked for vectorization, even when header duplication is
  66   // disabled.
  67   int Threshold = EnableHeaderDuplication ||
  68                           hasVectorizeTransformation(&L) == TM_ForcedByUser
  69                       ? DefaultRotationThreshold
  70                       : 0;
  71   const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
  72   const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
  73
  74   std::optional<MemorySSAUpdater> MSSAU;
  75   if (AR.MSSA)
  76     MSSAU = MemorySSAUpdater(AR.MSSA);
  77   bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
  78                               MSSAU ? &*MSSAU : nullptr, SQ, false, Threshold,
  79                               false, PrepareForLTO || PrepareForLTOOption);
  80
  81   if (!Changed)
  82     return PreservedAnalyses::all();
  83
  84   if (AR.MSSA && VerifyMemorySSA)
  85     AR.MSSA->verifyMemorySSA();
  86
  87   auto PA = getLoopPassPreservedAnalyses();
  88   if (AR.MSSA)
  89     PA.preserve<MemorySSAAnalysis>();
  90   return PA;
  91 }
  92
  93 namespace {
  94
  95 class LoopRotateLegacyPass : public LoopPass {
  96   unsigned MaxHeaderSize;
  97   bool PrepareForLTO;
  98
  99 public:
 100   static char ID; // Pass ID, replacement for typeid
 101   LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1,
 102                        bool PrepareForLTO = false)
 103       : LoopPass(ID), PrepareForLTO(PrepareForLTO) {
 104     initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
 105     if (SpecifiedMaxHeaderSize == -1)
 106       MaxHeaderSize = DefaultRotationThreshold;
 107     else
 108       MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
 109   }
 110
 111   // LCSSA form makes instruction renaming easier.
 112   void getAnalysisUsage(AnalysisUsage &AU) const override {
 113     AU.addRequired<AssumptionCacheTracker>();
 114     AU.addRequired<TargetTransformInfoWrapperPass>();
 115     AU.addPreserved<MemorySSAWrapperPass>();
 116     getLoopAnalysisUsage(AU);
 117
 118     // Lazy BFI and BPI are marked as preserved here so LoopRotate
 119     // can remain part of the same loop pass manager as LICM.
 120     AU.addPreserved<LazyBlockFrequencyInfoPass>();
 121     AU.addPreserved<LazyBranchProbabilityInfoPass>();
 122   }
 123
 124   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
 125     if (skipLoop(L))
 126       return false;
 127     Function &F = *L->getHeader()->getParent();
 128
 129     auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 130     const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
 131     auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 132     auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 133     auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
 134     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
 135     std::optional<MemorySSAUpdater> MSSAU;
 136     // Not requiring MemorySSA and getting it only if available will split
 137     // the loop pass pipeline when LoopRotate is being run first.
 138     auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
 139     if (MSSAA)
 140       MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
 141     // Vectorization requires loop-rotation. Use default threshold for loops the
 142     // user explicitly marked for vectorization, even when header duplication is
 143     // disabled.
 144     int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
 145                         ? DefaultRotationThreshold
 146                         : MaxHeaderSize;
 147
 148     return LoopRotation(L, LI, TTI, AC, &DT, &SE, MSSAU ? &*MSSAU : nullptr, SQ,
 149                         false, Threshold, false,
 150                         PrepareForLTO || PrepareForLTOOption);
 151   }
 152 };
 153 } // end namespace
 154
 155 char LoopRotateLegacyPass::ID = 0;
 156 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
 157                       false, false)
 158 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 159 INITIALIZE_PASS_DEPENDENCY(LoopPass)
 160 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 161 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
 162 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
 163                     false)
 164
 165 Pass *llvm::createLoopRotatePass(int MaxHeaderSize, bool PrepareForLTO) {
 166   return new LoopRotateLegacyPass(MaxHeaderSize, PrepareForLTO);
 167 }