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[Serialization] Use specialized decl hash function for GlobalDeclID #95730

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Merged
merged 2 commits into from
Jun 18, 2024
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[Serialization] Use specialized decl hash function for GlobalDeclID #95730

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[Serialization] Use specialized decl hash function for GlobalDeclID
ChuanqiXu9 Jun 17, 2024
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ChuanqiXu9 Jun 18, 2024
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6 changes: 5 additions & 1 deletion clang/include/clang/AST/DeclID.h
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Original file line number Diff line number Diff line change
Expand Up @@ -230,7 +230,11 @@ template <> struct DenseMapInfo<clang::GlobalDeclID> {
}

static unsigned getHashValue(const GlobalDeclID &Key) {
return DenseMapInfo<DeclID>::getHashValue(Key.get());
// Our default hash algorithm for 64 bits integer may not be very good.
// In GlobalDeclID's case, it is pretty common that the lower 32 bits can
// be same.
return DenseMapInfo<uint32_t>::getHashValue(Key.getModuleFileIndex()) ^
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Can you use hash_combine from llvm/ADT/Hash.h?

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@ilya-biryukov ilya-biryukov Jun 17, 2024 •
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+1 to using hash_combine, it should provide better results than xor.
Update: after asking around, I think hash_value from ADT/Hashing.h on the underlying int64 value would give good results here and make the code even simpler.

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Done

DenseMapInfo<uint32_t>::getHashValue(Key.getLocalDeclIndex());
}

static bool isEqual(const GlobalDeclID &L, const GlobalDeclID &R) {
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