[PATCH] D113613: [ThinLTO][MC] Use conditional assignments for promotion aliases

[Sami Tolvanen via Phabricator via llvm-commits]

samitolvanen created this revision.
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Inline assembly refererences to static functions with ThinLTO+CFI were
fixed in D104058 <https://reviews.llvm.org/D104058> by creating aliases for promoted functions. Creating
the aliases unconditionally resulted in an unexpected size increase in
a Chrome helper binary:

https://bugs.chromium.org/p/chromium/issues/detail?id=1261715

This is caused by the compiler being unable to drop unused code now
referenced by the alias in module-level inline assembly. This change
adds a .set_conditional assembly extension, which emits an assignment
only if the target symbol is also emitted, avoiding phantom references
to functions that could have otherwise been dropped.

This is an alternative to the solution proposed in D112761 <https://reviews.llvm.org/D112761>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D113613

Files:
  llvm/include/llvm/MC/MCStreamer.h
  llvm/lib/MC/MCParser/AsmParser.cpp
  llvm/lib/MC/MCStreamer.cpp
  llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
  llvm/test/MC/ELF/set-conditional.s
  llvm/test/ThinLTO/X86/devirt2.ll
  llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-icall-static-inline-asm.ll

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