[llvm] [LTO] Drop the weak function if there is a non-weak global symbol (PR #76287)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson requested changes to this pull request.

@cachemeifyoucan since afaict this is specific to users of the legacy LTO interfaces. Hoping you can give some insight into where this is best handled and how it works via ld64.

I don't think the handling should be down in the ModuleLinker. To clarify, this does not appear to be a general LTO issue, but you are changing the module linking used by some of the legacy LTO interfaces (e.g. llvm-lto and llvm-link). The new LTO api used by lld, gold plugin, and llvm-lto2 handle this already (in llvm/lib/LTO/LTO.cpp, we decide which symbols to keep when invoking the IRMover based on prevailing info from the linker, and it also processes the asm symbols in the ModuleSymbolTable).

I also believe this is likely handled ok by ld64 which uses the legacy LTO APIs as well, because the ModuleSymbolTable already contains parsed asm symbols, and it has ways of querying that information.

Looking at the linked earlier alternative PR, it looks like this is to fix rust LTO linking that uses llvm-link directly? Here though the tests use llvm-lto. Is rust using one of these tools or is it interfacing with the module linking directly via LLVM libraries? I'm really not sure where in the legacy LTO this handling should go. Note that llvm-lto already creates an LTOModule that contains a ModuleSymbolTable that already has these asm symbols.

https://github.com/llvm/llvm-project/pull/76287