forked from OSchip/llvm-project
341 lines
12 KiB
C++
341 lines
12 KiB
C++
//===-------- LoopDataPrefetch.cpp - Loop Data Prefetching Pass -----------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements a Loop Data Prefetching Pass.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Transforms/Scalar/LoopDataPrefetch.h"
|
|
|
|
#define DEBUG_TYPE "loop-data-prefetch"
|
|
#include "llvm/ADT/DepthFirstIterator.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/Analysis/AssumptionCache.h"
|
|
#include "llvm/Analysis/CodeMetrics.h"
|
|
#include "llvm/Analysis/InstructionSimplify.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Analysis/OptimizationDiagnosticInfo.h"
|
|
#include "llvm/Analysis/ScalarEvolution.h"
|
|
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
|
|
#include "llvm/Analysis/ScalarEvolutionExpander.h"
|
|
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
|
|
#include "llvm/Analysis/TargetTransformInfo.h"
|
|
#include "llvm/Analysis/ValueTracking.h"
|
|
#include "llvm/IR/CFG.h"
|
|
#include "llvm/IR/Dominators.h"
|
|
#include "llvm/IR/Function.h"
|
|
#include "llvm/IR/IntrinsicInst.h"
|
|
#include "llvm/IR/Module.h"
|
|
#include "llvm/Support/CommandLine.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/Transforms/Utils/ValueMapper.h"
|
|
using namespace llvm;
|
|
|
|
// By default, we limit this to creating 16 PHIs (which is a little over half
|
|
// of the allocatable register set).
|
|
static cl::opt<bool>
|
|
PrefetchWrites("loop-prefetch-writes", cl::Hidden, cl::init(false),
|
|
cl::desc("Prefetch write addresses"));
|
|
|
|
static cl::opt<unsigned>
|
|
PrefetchDistance("prefetch-distance",
|
|
cl::desc("Number of instructions to prefetch ahead"),
|
|
cl::Hidden);
|
|
|
|
static cl::opt<unsigned>
|
|
MinPrefetchStride("min-prefetch-stride",
|
|
cl::desc("Min stride to add prefetches"), cl::Hidden);
|
|
|
|
static cl::opt<unsigned> MaxPrefetchIterationsAhead(
|
|
"max-prefetch-iters-ahead",
|
|
cl::desc("Max number of iterations to prefetch ahead"), cl::Hidden);
|
|
|
|
STATISTIC(NumPrefetches, "Number of prefetches inserted");
|
|
|
|
namespace {
|
|
|
|
/// Loop prefetch implementation class.
|
|
class LoopDataPrefetch {
|
|
public:
|
|
LoopDataPrefetch(AssumptionCache *AC, LoopInfo *LI, ScalarEvolution *SE,
|
|
const TargetTransformInfo *TTI,
|
|
OptimizationRemarkEmitter *ORE)
|
|
: AC(AC), LI(LI), SE(SE), TTI(TTI), ORE(ORE) {}
|
|
|
|
bool run();
|
|
|
|
private:
|
|
bool runOnLoop(Loop *L);
|
|
|
|
/// \brief Check if the the stride of the accesses is large enough to
|
|
/// warrant a prefetch.
|
|
bool isStrideLargeEnough(const SCEVAddRecExpr *AR);
|
|
|
|
unsigned getMinPrefetchStride() {
|
|
if (MinPrefetchStride.getNumOccurrences() > 0)
|
|
return MinPrefetchStride;
|
|
return TTI->getMinPrefetchStride();
|
|
}
|
|
|
|
unsigned getPrefetchDistance() {
|
|
if (PrefetchDistance.getNumOccurrences() > 0)
|
|
return PrefetchDistance;
|
|
return TTI->getPrefetchDistance();
|
|
}
|
|
|
|
unsigned getMaxPrefetchIterationsAhead() {
|
|
if (MaxPrefetchIterationsAhead.getNumOccurrences() > 0)
|
|
return MaxPrefetchIterationsAhead;
|
|
return TTI->getMaxPrefetchIterationsAhead();
|
|
}
|
|
|
|
AssumptionCache *AC;
|
|
LoopInfo *LI;
|
|
ScalarEvolution *SE;
|
|
const TargetTransformInfo *TTI;
|
|
OptimizationRemarkEmitter *ORE;
|
|
};
|
|
|
|
/// Legacy class for inserting loop data prefetches.
|
|
class LoopDataPrefetchLegacyPass : public FunctionPass {
|
|
public:
|
|
static char ID; // Pass ID, replacement for typeid
|
|
LoopDataPrefetchLegacyPass() : FunctionPass(ID) {
|
|
initializeLoopDataPrefetchLegacyPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
AU.addPreserved<DominatorTreeWrapperPass>();
|
|
AU.addRequired<LoopInfoWrapperPass>();
|
|
AU.addPreserved<LoopInfoWrapperPass>();
|
|
AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
|
|
AU.addRequired<ScalarEvolutionWrapperPass>();
|
|
// FIXME: For some reason, preserving SE here breaks LSR (even if
|
|
// this pass changes nothing).
|
|
// AU.addPreserved<ScalarEvolutionWrapperPass>();
|
|
AU.addRequired<TargetTransformInfoWrapperPass>();
|
|
}
|
|
|
|
bool runOnFunction(Function &F) override;
|
|
};
|
|
}
|
|
|
|
char LoopDataPrefetchLegacyPass::ID = 0;
|
|
INITIALIZE_PASS_BEGIN(LoopDataPrefetchLegacyPass, "loop-data-prefetch",
|
|
"Loop Data Prefetch", false, false)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
|
|
INITIALIZE_PASS_END(LoopDataPrefetchLegacyPass, "loop-data-prefetch",
|
|
"Loop Data Prefetch", false, false)
|
|
|
|
FunctionPass *llvm::createLoopDataPrefetchPass() {
|
|
return new LoopDataPrefetchLegacyPass();
|
|
}
|
|
|
|
bool LoopDataPrefetch::isStrideLargeEnough(const SCEVAddRecExpr *AR) {
|
|
unsigned TargetMinStride = getMinPrefetchStride();
|
|
// No need to check if any stride goes.
|
|
if (TargetMinStride <= 1)
|
|
return true;
|
|
|
|
const auto *ConstStride = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
|
|
// If MinStride is set, don't prefetch unless we can ensure that stride is
|
|
// larger.
|
|
if (!ConstStride)
|
|
return false;
|
|
|
|
unsigned AbsStride = std::abs(ConstStride->getAPInt().getSExtValue());
|
|
return TargetMinStride <= AbsStride;
|
|
}
|
|
|
|
PreservedAnalyses LoopDataPrefetchPass::run(Function &F,
|
|
FunctionAnalysisManager &AM) {
|
|
LoopInfo *LI = &AM.getResult<LoopAnalysis>(F);
|
|
ScalarEvolution *SE = &AM.getResult<ScalarEvolutionAnalysis>(F);
|
|
AssumptionCache *AC = &AM.getResult<AssumptionAnalysis>(F);
|
|
OptimizationRemarkEmitter *ORE =
|
|
&AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
|
|
const TargetTransformInfo *TTI = &AM.getResult<TargetIRAnalysis>(F);
|
|
|
|
LoopDataPrefetch LDP(AC, LI, SE, TTI, ORE);
|
|
bool Changed = LDP.run();
|
|
|
|
if (Changed) {
|
|
PreservedAnalyses PA;
|
|
PA.preserve<DominatorTreeAnalysis>();
|
|
PA.preserve<LoopAnalysis>();
|
|
return PA;
|
|
}
|
|
|
|
return PreservedAnalyses::all();
|
|
}
|
|
|
|
bool LoopDataPrefetchLegacyPass::runOnFunction(Function &F) {
|
|
if (skipFunction(F))
|
|
return false;
|
|
|
|
LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
|
|
ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
|
|
AssumptionCache *AC =
|
|
&getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
|
|
OptimizationRemarkEmitter *ORE =
|
|
&getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
|
|
const TargetTransformInfo *TTI =
|
|
&getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
|
|
|
|
LoopDataPrefetch LDP(AC, LI, SE, TTI, ORE);
|
|
return LDP.run();
|
|
}
|
|
|
|
bool LoopDataPrefetch::run() {
|
|
// If PrefetchDistance is not set, don't run the pass. This gives an
|
|
// opportunity for targets to run this pass for selected subtargets only
|
|
// (whose TTI sets PrefetchDistance).
|
|
if (getPrefetchDistance() == 0)
|
|
return false;
|
|
assert(TTI->getCacheLineSize() && "Cache line size is not set for target");
|
|
|
|
bool MadeChange = false;
|
|
|
|
for (Loop *I : *LI)
|
|
for (auto L = df_begin(I), LE = df_end(I); L != LE; ++L)
|
|
MadeChange |= runOnLoop(*L);
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
bool LoopDataPrefetch::runOnLoop(Loop *L) {
|
|
bool MadeChange = false;
|
|
|
|
// Only prefetch in the inner-most loop
|
|
if (!L->empty())
|
|
return MadeChange;
|
|
|
|
SmallPtrSet<const Value *, 32> EphValues;
|
|
CodeMetrics::collectEphemeralValues(L, AC, EphValues);
|
|
|
|
// Calculate the number of iterations ahead to prefetch
|
|
CodeMetrics Metrics;
|
|
for (const auto BB : L->blocks()) {
|
|
// If the loop already has prefetches, then assume that the user knows
|
|
// what they are doing and don't add any more.
|
|
for (auto &I : *BB)
|
|
if (CallInst *CI = dyn_cast<CallInst>(&I))
|
|
if (Function *F = CI->getCalledFunction())
|
|
if (F->getIntrinsicID() == Intrinsic::prefetch)
|
|
return MadeChange;
|
|
|
|
Metrics.analyzeBasicBlock(BB, *TTI, EphValues);
|
|
}
|
|
unsigned LoopSize = Metrics.NumInsts;
|
|
if (!LoopSize)
|
|
LoopSize = 1;
|
|
|
|
unsigned ItersAhead = getPrefetchDistance() / LoopSize;
|
|
if (!ItersAhead)
|
|
ItersAhead = 1;
|
|
|
|
if (ItersAhead > getMaxPrefetchIterationsAhead())
|
|
return MadeChange;
|
|
|
|
DEBUG(dbgs() << "Prefetching " << ItersAhead
|
|
<< " iterations ahead (loop size: " << LoopSize << ") in "
|
|
<< L->getHeader()->getParent()->getName() << ": " << *L);
|
|
|
|
SmallVector<std::pair<Instruction *, const SCEVAddRecExpr *>, 16> PrefLoads;
|
|
for (const auto BB : L->blocks()) {
|
|
for (auto &I : *BB) {
|
|
Value *PtrValue;
|
|
Instruction *MemI;
|
|
|
|
if (LoadInst *LMemI = dyn_cast<LoadInst>(&I)) {
|
|
MemI = LMemI;
|
|
PtrValue = LMemI->getPointerOperand();
|
|
} else if (StoreInst *SMemI = dyn_cast<StoreInst>(&I)) {
|
|
if (!PrefetchWrites) continue;
|
|
MemI = SMemI;
|
|
PtrValue = SMemI->getPointerOperand();
|
|
} else continue;
|
|
|
|
unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
|
|
if (PtrAddrSpace)
|
|
continue;
|
|
|
|
if (L->isLoopInvariant(PtrValue))
|
|
continue;
|
|
|
|
const SCEV *LSCEV = SE->getSCEV(PtrValue);
|
|
const SCEVAddRecExpr *LSCEVAddRec = dyn_cast<SCEVAddRecExpr>(LSCEV);
|
|
if (!LSCEVAddRec)
|
|
continue;
|
|
|
|
// Check if the the stride of the accesses is large enough to warrant a
|
|
// prefetch.
|
|
if (!isStrideLargeEnough(LSCEVAddRec))
|
|
continue;
|
|
|
|
// We don't want to double prefetch individual cache lines. If this load
|
|
// is known to be within one cache line of some other load that has
|
|
// already been prefetched, then don't prefetch this one as well.
|
|
bool DupPref = false;
|
|
for (const auto &PrefLoad : PrefLoads) {
|
|
const SCEV *PtrDiff = SE->getMinusSCEV(LSCEVAddRec, PrefLoad.second);
|
|
if (const SCEVConstant *ConstPtrDiff =
|
|
dyn_cast<SCEVConstant>(PtrDiff)) {
|
|
int64_t PD = std::abs(ConstPtrDiff->getValue()->getSExtValue());
|
|
if (PD < (int64_t) TTI->getCacheLineSize()) {
|
|
DupPref = true;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
if (DupPref)
|
|
continue;
|
|
|
|
const SCEV *NextLSCEV = SE->getAddExpr(LSCEVAddRec, SE->getMulExpr(
|
|
SE->getConstant(LSCEVAddRec->getType(), ItersAhead),
|
|
LSCEVAddRec->getStepRecurrence(*SE)));
|
|
if (!isSafeToExpand(NextLSCEV, *SE))
|
|
continue;
|
|
|
|
PrefLoads.push_back(std::make_pair(MemI, LSCEVAddRec));
|
|
|
|
Type *I8Ptr = Type::getInt8PtrTy(BB->getContext(), PtrAddrSpace);
|
|
SCEVExpander SCEVE(*SE, I.getModule()->getDataLayout(), "prefaddr");
|
|
Value *PrefPtrValue = SCEVE.expandCodeFor(NextLSCEV, I8Ptr, MemI);
|
|
|
|
IRBuilder<> Builder(MemI);
|
|
Module *M = BB->getParent()->getParent();
|
|
Type *I32 = Type::getInt32Ty(BB->getContext());
|
|
Value *PrefetchFunc = Intrinsic::getDeclaration(M, Intrinsic::prefetch);
|
|
Builder.CreateCall(
|
|
PrefetchFunc,
|
|
{PrefPtrValue,
|
|
ConstantInt::get(I32, MemI->mayReadFromMemory() ? 0 : 1),
|
|
ConstantInt::get(I32, 3), ConstantInt::get(I32, 1)});
|
|
++NumPrefetches;
|
|
DEBUG(dbgs() << " Access: " << *PtrValue << ", SCEV: " << *LSCEV
|
|
<< "\n");
|
|
ORE->emitOptimizationRemark(DEBUG_TYPE, MemI, "prefetched memory access");
|
|
|
|
MadeChange = true;
|
|
}
|
|
}
|
|
|
|
return MadeChange;
|
|
}
|
|
|