[PATCH] D140606: [lld-macho] Only fold private-label aliases that do not have flags

[Jez Ng via Phabricator via llvm-commits]

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This will enable us to re-land D139069: [lld-macho] Private label aliases to weak symbols should not retain section data <https://reviews.llvm.org/D139069>.

The issue with the original diff was that we were folding all
private-label symbols. We were not merging the symbol flags during this
folding; instead we just made all references to the folded symbol point
to its aliasee. This caused some flags to be incorrectly discarded. This
surfaced as code that was incorrectly stripped due to LLD dropping the
`.no_dead_strip` flag.

This diff fixes things by only folding flag-less private-label aliases.
Most (maybe all) of the `ltmp<N>` symbols that are generated by the MC
aarch64 backend are flag-less, so this conservative folding behavior
does the job.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140606

Files:
  lld/MachO/InputFiles.cpp
  lld/test/MachO/weak-def-alias-private-label.s

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