Fangrui Song 53544fc15f [ELF] Respect ltoCanOmit for symbols in non-prevailing COMDAT ...

A linkonce_odr definition can be omitted in LTO compilation if
`canBeOmittedFromSymbolTable()` is true in all bitcode files.

Currently, we don't respect the `canBeOmittedFromSymbolTable()` bit from
symbols in a non-prevailing COMDAT, which could lead to incorrect
omission of a definition when merging a prevailing linkonce_odr and a
non-prevailing weak_odr, e.g. an implicit template instantiation and an
explicit template instantiation.

To fix #111341, allow the non-prevailing COMDAT code path to clear the
`ltoCanOmit` bit, so that `VisibleToRegularObj` could be false in
LTO.cpp. We could resolve either an Undefined or a Defined. For
simplicity, just use a Defined like the prevailing case (similar to how
we resolve symbols in ObjectFile COMDAT reviews.llvm.org/D120626).

Pull Request: https://github.com/llvm/llvm-project/pull/119332

2024-12-11 08:55:05 -08:00

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