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/ADT/Statistic.h"
  15 #include "llvm/Analysis/AssumptionCache.h"
  16 #include "llvm/Analysis/InstructionSimplify.h"
  17 #include "llvm/Analysis/LazyBlockFrequencyInfo.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/Support/Debug.h"
  26 #include "llvm/Transforms/Scalar.h"
  27 #include "llvm/Transforms/Scalar/LoopPassManager.h"
  28 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
  29 #include "llvm/Transforms/Utils/LoopUtils.h"
  30 using namespace llvm;
  31
  32 #define DEBUG_TYPE "loop-rotate"
  33
  34 static cl::opt<unsigned> DefaultRotationThreshold(
  35     "rotation-max-header-size", cl::init(16), cl::Hidden,
  36     cl::desc("The default maximum header size for automatic loop rotation"));
  37
  38 static cl::opt<bool> PrepareForLTOOption(
  39     "rotation-prepare-for-lto", cl::init(false), cl::Hidden,
  40     cl::desc("Run loop-rotation in the prepare-for-lto stage. This option "
  41              "should be used for testing only."));
  42
  43 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO)
  44     : EnableHeaderDuplication(EnableHeaderDuplication),
  45       PrepareForLTO(PrepareForLTO) {}
  46
  47 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
  48                                       LoopStandardAnalysisResults &AR,
  49                                       LPMUpdater &) {
  50   // Vectorization requires loop-rotation. Use default threshold for loops the
  51   // user explicitly marked for vectorization, even when header duplication is
  52   // disabled.
  53   int Threshold = EnableHeaderDuplication ||
  54                           hasVectorizeTransformation(&L) == TM_ForcedByUser
  55                       ? DefaultRotationThreshold
  56                       : 0;
  57   const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
  58   const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
  59
  60   Optional<MemorySSAUpdater> MSSAU;
  61   if (AR.MSSA)
  62     MSSAU = MemorySSAUpdater(AR.MSSA);
  63   bool Changed =
  64       LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
  65                    MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ, false,
  66                    Threshold, false, PrepareForLTO || PrepareForLTOOption);
  67
  68   if (!Changed)
  69     return PreservedAnalyses::all();
  70
  71   if (AR.MSSA && VerifyMemorySSA)
  72     AR.MSSA->verifyMemorySSA();
  73
  74   auto PA = getLoopPassPreservedAnalyses();
  75   if (AR.MSSA)
  76     PA.preserve<MemorySSAAnalysis>();
  77   return PA;
  78 }
  79
  80 namespace {
  81
  82 class LoopRotateLegacyPass : public LoopPass {
  83   unsigned MaxHeaderSize;
  84   bool PrepareForLTO;
  85
  86 public:
  87   static char ID; // Pass ID, replacement for typeid
  88   LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1,
  89                        bool PrepareForLTO = false)
  90       : LoopPass(ID), PrepareForLTO(PrepareForLTO) {
  91     initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
  92     if (SpecifiedMaxHeaderSize == -1)
  93       MaxHeaderSize = DefaultRotationThreshold;
  94     else
  95       MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
  96   }
  97
  98   // LCSSA form makes instruction renaming easier.
  99   void getAnalysisUsage(AnalysisUsage &AU) const override {
 100     AU.addRequired<AssumptionCacheTracker>();
 101     AU.addRequired<TargetTransformInfoWrapperPass>();
 102     AU.addPreserved<MemorySSAWrapperPass>();
 103     getLoopAnalysisUsage(AU);
 104
 105     // Lazy BFI and BPI are marked as preserved here so LoopRotate
 106     // can remain part of the same loop pass manager as LICM.
 107     AU.addPreserved<LazyBlockFrequencyInfoPass>();
 108     AU.addPreserved<LazyBranchProbabilityInfoPass>();
 109   }
 110
 111   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
 112     if (skipLoop(L))
 113       return false;
 114     Function &F = *L->getHeader()->getParent();
 115
 116     auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 117     const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
 118     auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
 119     auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 120     auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
 121     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
 122     Optional<MemorySSAUpdater> MSSAU;
 123     // Not requiring MemorySSA and getting it only if available will split
 124     // the loop pass pipeline when LoopRotate is being run first.
 125     auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
 126     if (MSSAA)
 127       MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
 128     // Vectorization requires loop-rotation. Use default threshold for loops the
 129     // user explicitly marked for vectorization, even when header duplication is
 130     // disabled.
 131     int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
 132                         ? DefaultRotationThreshold
 133                         : MaxHeaderSize;
 134
 135     return LoopRotation(L, LI, TTI, AC, &DT, &SE,
 136                         MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
 137                         false, Threshold, false,
 138                         PrepareForLTO || PrepareForLTOOption);
 139   }
 140 };
 141 } // end namespace
 142
 143 char LoopRotateLegacyPass::ID = 0;
 144 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
 145                       false, false)
 146 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 147 INITIALIZE_PASS_DEPENDENCY(LoopPass)
 148 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 149 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
 150 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
 151                     false)
 152
 153 Pass *llvm::createLoopRotatePass(int MaxHeaderSize, bool PrepareForLTO) {
 154   return new LoopRotateLegacyPass(MaxHeaderSize, PrepareForLTO);
 155 }