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[InstrProf] Change step from 64-bit to pointer-sized int #83239

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[InstrProf] Change step from 64-bit to pointer-sized int #83239

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1 change: 1 addition & 0 deletions llvm/include/llvm/IR/IntrinsicInst.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1506,6 +1506,7 @@ class InstrProfIncrementInst : public InstrProfCntrInstBase {
return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
}
Value *getStep() const;
Value *getAtomicStep() const;
};

/// This represents the llvm.instrprof.increment.step intrinsic.
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17 changes: 17 additions & 0 deletions llvm/lib/IR/IntrinsicInst.cpp
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Expand Up @@ -288,9 +288,26 @@ Value *InstrProfIncrementInst::getStep() const {
}
const Module *M = getModule();
LLVMContext &Context = M->getContext();
const auto &DL = M->getDataLayout();
Type *LargestLegalIntTy = DL.getLargestLegalIntType(Context);

if (LargestLegalIntTy) {
return ConstantInt::get(LargestLegalIntTy, 1);
}

return ConstantInt::get(Type::getInt64Ty(Context), 1);
}

Value *InstrProfIncrementInst::getAtomicStep() const {
if (InstrProfIncrementInstStep::classof(this)) {
return const_cast<Value *>(getArgOperand(4));
}
const Module *M = getModule();
LLVMContext &Context = M->getContext();
const auto &DL = M->getDataLayout();
return ConstantInt::get(DL.getIntPtrType(Context), 1);
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With a 64-bit type, very few counters will overflow. With a pointer-width type, more counters will overflow, especially on 16-bit targets, but even on 32-bit targets. I speculate this is why 64-bit integers are used currently. How should we address this concern?

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I see. I pushed some changes, creating additional getStep function for atomics. This way, we can use a larger type.

Also, I've taken the liberty of changing the existing code to use the largest legal int available instead of the 64-bit int.

}

std::optional<RoundingMode> ConstrainedFPIntrinsic::getRoundingMode() const {
unsigned NumOperands = arg_size();
Metadata *MD = nullptr;
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2 changes: 1 addition & 1 deletion llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
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Expand Up @@ -958,7 +958,7 @@ void InstrLowerer::lowerIncrement(InstrProfIncrementInst *Inc) {
IRBuilder<> Builder(Inc);
if (Options.Atomic || AtomicCounterUpdateAll ||
(Inc->getIndex()->isZeroValue() && AtomicFirstCounter)) {
Builder.CreateAtomicRMW(AtomicRMWInst::Add, Addr, Inc->getStep(),
Builder.CreateAtomicRMW(AtomicRMWInst::Add, Addr, Inc->getAtomicStep(),
MaybeAlign(), AtomicOrdering::Monotonic);
} else {
Value *IncStep = Inc->getStep();
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