[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

lld/ELF/MarkLive.cpp

@@ -152,8 +152,8 @@ 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)
+    for (size_t j = firstRelI, end2 = rels.size();
+         j < end2 && rels[j].r_offset < pieceEnd; ++j)
       resolveReloc(eh, rels[j], true);
   }
 }