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//===-------- PPCLoopDataPrefetch.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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ppc-loop-data-prefetch"
#include "PPC.h"
#include "llvm/Transforms/Scalar.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/ScalarEvolution.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/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("ppc-loop-prefetch-writes", cl::Hidden, cl::init(false),
cl::desc("Prefetch write addresses"));
// This seems like a reasonable default for the BG/Q (this pass is enabled, by
// default, only on the BG/Q).
static cl::opt<unsigned>
PrefDist("ppc-loop-prefetch-distance", cl::Hidden, cl::init(300),
cl::desc("The loop prefetch distance"));
static cl::opt<unsigned>
CacheLineSize("ppc-loop-prefetch-cache-line", cl::Hidden, cl::init(64),
cl::desc("The loop prefetch cache line size"));
namespace llvm {
void initializePPCLoopDataPrefetchPass(PassRegistry&);
}
namespace {
class PPCLoopDataPrefetch : public FunctionPass {
public:
static char ID; // Pass ID, replacement for typeid
PPCLoopDataPrefetch() : FunctionPass(ID) {
initializePPCLoopDataPrefetchPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequired<ScalarEvolution>();
// FIXME: For some reason, preserving SE here breaks LSR (even if
// this pass changes nothing).
// AU.addPreserved<ScalarEvolution>();
AU.addRequired<TargetTransformInfoWrapperPass>();
}
bool runOnFunction(Function &F) override;
bool runOnLoop(Loop *L);
private:
AssumptionCache *AC;
LoopInfo *LI;
ScalarEvolution *SE;
const TargetTransformInfo *TTI;
const DataLayout *DL;
};
}
char PPCLoopDataPrefetch::ID = 0;
INITIALIZE_PASS_BEGIN(PPCLoopDataPrefetch, "ppc-loop-data-prefetch",
"PPC Loop Data Prefetch", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_END(PPCLoopDataPrefetch, "ppc-loop-data-prefetch",
"PPC Loop Data Prefetch", false, false)
FunctionPass *llvm::createPPCLoopDataPrefetchPass() { return new PPCLoopDataPrefetch(); }
bool PPCLoopDataPrefetch::runOnFunction(Function &F) {
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
SE = &getAnalysis<ScalarEvolution>();
DL = &F.getParent()->getDataLayout();
AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
bool MadeChange = false;
for (LoopInfo::iterator I = LI->begin(), E = LI->end();
I != E; ++I) {
Loop *L = *I;
MadeChange |= runOnLoop(L);
}
return MadeChange;
}
bool PPCLoopDataPrefetch::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 (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
I != IE; ++I) {
// If the loop already has prefetches, then assume that the user knows
// what he or she is doing and don't add any more.
for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
J != JE; ++J)
if (CallInst *CI = dyn_cast<CallInst>(J))
if (Function *F = CI->getCalledFunction())
if (F->getIntrinsicID() == Intrinsic::prefetch)
return MadeChange;
Metrics.analyzeBasicBlock(*I, *TTI, EphValues);
}
unsigned LoopSize = Metrics.NumInsts;
if (!LoopSize)
LoopSize = 1;
unsigned ItersAhead = PrefDist/LoopSize;
if (!ItersAhead)
ItersAhead = 1;
SmallVector<std::pair<Instruction *, const SCEVAddRecExpr *>, 16> PrefLoads;
for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
I != IE; ++I) {
for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
J != JE; ++J) {
Value *PtrValue;
Instruction *MemI;
if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
MemI = LMemI;
PtrValue = LMemI->getPointerOperand();
} else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
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;
// 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 (SmallVector<std::pair<Instruction *, const SCEVAddRecExpr *>,
16>::iterator K = PrefLoads.begin(), KE = PrefLoads.end();
K != KE; ++K) {
const SCEV *PtrDiff = SE->getMinusSCEV(LSCEVAddRec, K->second);
if (const SCEVConstant *ConstPtrDiff =
dyn_cast<SCEVConstant>(PtrDiff)) {
int64_t PD = std::abs(ConstPtrDiff->getValue()->getSExtValue());
if (PD < (int64_t) CacheLineSize) {
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((*I)->getContext(), PtrAddrSpace);
SCEVExpander SCEVE(*SE, J->getModule()->getDataLayout(), "prefaddr");
Value *PrefPtrValue = SCEVE.expandCodeFor(NextLSCEV, I8Ptr, MemI);
IRBuilder<> Builder(MemI);
Module *M = (*I)->getParent()->getParent();
Type *I32 = Type::getInt32Ty((*I)->getContext());
Value *PrefetchFunc = Intrinsic::getDeclaration(M, Intrinsic::prefetch);
Builder.CreateCall4(PrefetchFunc, PrefPtrValue,
ConstantInt::get(I32, MemI->mayReadFromMemory() ? 0 : 1),
ConstantInt::get(I32, 3), ConstantInt::get(I32, 1));
MadeChange = true;
}
}
return MadeChange;
}
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