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[LLD][ELF] Fix performance of MarkLive::scanEhFrameSection 

MarkLive::scanEhFrameSection is used to retain personality/LSDA
functions when --gc-sections is enabled.

Improve its performance by only iterating over the .eh_frame relocations
that need to be resolved for an EhSectionPiece. This optimization makes
the same assumption as elsewhere in LLD that the .eh_frame relocations
are sorted by r_offset.

This appears to be a performance regression introduced in commit
e6c24299d2 (https://reviews.llvm.org/D59800).

This change has been seen to reduce link time by up to ~50%.

Differential Revision: https://reviews.llvm.org/D87245
This commit is contained in:
Andrew Ng 2020-09-07 17:36:14 +01:00
parent ce49b7d9ca
commit 863aa0a37b
1 changed files with 3 additions and 3 deletions
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6
lld/ELF/MarkLive.cpp
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@ -152,9 +152,9 @@ void MarkLive<ELFT>::scanEhFrameSection(EhInputSection &eh,
// a LSDA. We only need to keep the LSDA alive, so ignore anything that
// points to executable sections.
uint64_t pieceEnd = piece.inputOff + piece.size;
for (size_t j = firstRelI, end2 = rels.size(); j < end2; ++j)
if (rels[j].r_offset < pieceEnd)
resolveReloc(eh, rels[j], true);
for (size_t j = firstRelI, end2 = rels.size();
j < end2 && rels[j].r_offset < pieceEnd; ++j)
resolveReloc(eh, rels[j], true);
}
}