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[MCA] Avoid repeated hash lookups (NFC) #129192

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Feb 28, 2025
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[MCA] Avoid repeated hash lookups (NFC) #129192

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6 changes: 2 additions & 4 deletions llvm/lib/MCA/InstrBuilder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -634,16 +634,14 @@ InstrBuilder::createInstrDescImpl(const MCInst &MCI,
bool IsVariadic = MCDesc.isVariadic();
if ((ID->IsRecyclable = !IsVariadic && !IsVariant)) {
auto DKey = std::make_pair(MCI.getOpcode(), SchedClassID);
Descriptors[DKey] = std::move(ID);
return *Descriptors[DKey];
return *(Descriptors[DKey] = std::move(ID));
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@adibiagio adibiagio Feb 28, 2025

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Apologies if I am a bit late on this review.

Have you considered using insert_or_assign() ?
https://llvm.org/doxygen/DenseMap_8h_source.html#l00306

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@adibiagio adibiagio Feb 28, 2025

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Using insert_or_assign() should solve the issue in a nicer way. That is, assuming that my understanding of how insert_or_assign() works is correct :) .

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@kazutakahirata kazutakahirata Feb 28, 2025

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I could use insert_or_assign, but that would be a bit mouthful though:

    return *(Descriptors[DKey] = std::move(ID));
    return *(Descriptors.insert_or_assign(DKey, std::move(ID)).first->second);

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@adibiagio adibiagio Feb 28, 2025

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Mmm yeah, it forces you to do that annoying first->second to get the iterator from the pair.
Nevermind then. Thanks for the fix!

}

auto VDKey = std::make_pair(hashMCInst(MCI), SchedClassID);
assert(
!VariantDescriptors.contains(VDKey) &&
"Expected VariantDescriptors to not already have a value for this key.");
VariantDescriptors[VDKey] = std::move(ID);
return *VariantDescriptors[VDKey];
return *(VariantDescriptors[VDKey] = std::move(ID));
}

Expected<const InstrDesc &>
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