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//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements Loop Rotation Pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LoopRotation.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyBlockFrequencyInfo.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/LoopRotationUtils.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include <optional>
using namespace llvm;
#define DEBUG_TYPE "loop-rotate"
static cl::opt<unsigned> DefaultRotationThreshold(
"rotation-max-header-size", cl::init(16), cl::Hidden,
cl::desc("The default maximum header size for automatic loop rotation"));
static cl::opt<bool> PrepareForLTOOption(
"rotation-prepare-for-lto", cl::init(false), cl::Hidden,
cl::desc("Run loop-rotation in the prepare-for-lto stage. This option "
"should be used for testing only."));
LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO)
: EnableHeaderDuplication(EnableHeaderDuplication),
PrepareForLTO(PrepareForLTO) {}
PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &) {
// Vectorization requires loop-rotation. Use default threshold for loops the
// user explicitly marked for vectorization, even when header duplication is
// disabled.
int Threshold = EnableHeaderDuplication ||
hasVectorizeTransformation(&L) == TM_ForcedByUser
? DefaultRotationThreshold
: 0;
const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
std::optional<MemorySSAUpdater> MSSAU;
if (AR.MSSA)
MSSAU = MemorySSAUpdater(AR.MSSA);
bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
MSSAU ? &*MSSAU : nullptr, SQ, false, Threshold,
false, PrepareForLTO || PrepareForLTOOption);
if (!Changed)
return PreservedAnalyses::all();
if (AR.MSSA && VerifyMemorySSA)
AR.MSSA->verifyMemorySSA();
auto PA = getLoopPassPreservedAnalyses();
if (AR.MSSA)
PA.preserve<MemorySSAAnalysis>();
return PA;
}
namespace {
class LoopRotateLegacyPass : public LoopPass {
unsigned MaxHeaderSize;
bool PrepareForLTO;
public:
static char ID; // Pass ID, replacement for typeid
LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1,
bool PrepareForLTO = false)
: LoopPass(ID), PrepareForLTO(PrepareForLTO) {
initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
if (SpecifiedMaxHeaderSize == -1)
MaxHeaderSize = DefaultRotationThreshold;
else
MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
}
// LCSSA form makes instruction renaming easier.
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addPreserved<MemorySSAWrapperPass>();
getLoopAnalysisUsage(AU);
// Lazy BFI and BPI are marked as preserved here so LoopRotate
// can remain part of the same loop pass manager as LICM.
AU.addPreserved<LazyBlockFrequencyInfoPass>();
AU.addPreserved<LazyBranchProbabilityInfoPass>();
}
bool runOnLoop(Loop *L, LPPassManager &LPM) override {
if (skipLoop(L))
return false;
Function &F = *L->getHeader()->getParent();
auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
std::optional<MemorySSAUpdater> MSSAU;
// Not requiring MemorySSA and getting it only if available will split
// the loop pass pipeline when LoopRotate is being run first.
auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
if (MSSAA)
MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
// Vectorization requires loop-rotation. Use default threshold for loops the
// user explicitly marked for vectorization, even when header duplication is
// disabled.
int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
? DefaultRotationThreshold
: MaxHeaderSize;
return LoopRotation(L, LI, TTI, AC, &DT, &SE, MSSAU ? &*MSSAU : nullptr, SQ,
false, Threshold, false,
PrepareForLTO || PrepareForLTOOption);
}
};
} // end namespace
char LoopRotateLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
false)
Pass *llvm::createLoopRotatePass(int MaxHeaderSize, bool PrepareForLTO) {
return new LoopRotateLegacyPass(MaxHeaderSize, PrepareForLTO);
}
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