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[KeyInstr] MDNodeKeyImpl<DILocation> skip zero values for hash (#143357)

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[KeyInstr] MDNodeKeyImpl<DILocation> skip zero values for hash

Hashing AtomGroup and AtomRank substantially impacts performance whether Key
Instructions is enabled or not. We can't detect whether it's enabled here
cheaply; avoiding hashing zero values is a good approximation. This affects
Key Instruction builds too, but any potential costs incurred by messing with
the hash distribution (hash_combine(x) != hash_combine(x, 0)) appear to still
be massively outweighed by the overall compile time savings by performing this
check.

See PR for compile-time-tracker numbers.
This commit is contained in:
Orlando Cazalet-Hyams
2025-06-09 14:50:33 +01:00
committed by GitHub
parent e4060d3bea
commit cf5e2b613d
1 changed files with 11 additions and 5 deletions
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16
llvm/lib/IR/LLVMContextImpl.h
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@@ -355,13 +355,19 @@ template <> struct MDNodeKeyImpl<DILocation> {
}
unsigned getHashValue() const {
return hash_combine(Line, Column, Scope, InlinedAt, ImplicitCode
#ifdef EXPERIMENTAL_KEY_INSTRUCTIONS
,
AtomGroup, (uint8_t)AtomRank);
#else
);
// Hashing AtomGroup and AtomRank substantially impacts performance whether
// Key Instructions is enabled or not. We can't detect whether it's enabled
// here cheaply; avoiding hashing zero values is a good approximation. This
// affects Key Instruction builds too, but any potential costs incurred by
// messing with the hash distribution* appear to still be massively
// outweighed by the overall compile time savings by performing this check.
// * (hash_combine(x) != hash_combine(x, 0))
if (AtomGroup || AtomRank)
return hash_combine(Line, Column, Scope, InlinedAt, ImplicitCode,
AtomGroup, (uint8_t)AtomRank);
#endif
return hash_combine(Line, Column, Scope, InlinedAt, ImplicitCode);
}
};