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;
}
