[PATCH] D106228: [LTO] Add SelectionKind to IRSymtab and use it in ld.lld/LLVMgold

[Fangrui Song via Phabricator via llvm-commits]

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In PGO, a C++ external linkage function `foo` has a private counter
`__profc_foo` and a private `__profd_foo` in a `comdat noduplicates`.

A `__attribute__((weak))` function `foo` has a weak hidden counter `__profc_foo`
and a private `__profd_foo` in a `comdat noduplicates`.

In `ld.lld a.o b.o`, say a.o defines an external linkage `foo` and b.o
defines a weak `foo`. Currently we treat `comdat noduplicates` as `comdat any`,
ld.lld will incorrectly consider `b.o:__profc_foo` non-prevailing.  In the worst
case `b.o:__profd_foo` is retained and `b.o:__profc_foo` isn't there will be
dangling reference causing an `undefined hidden symbol` error.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106228

Files:
  lld/COFF/InputFiles.cpp
  lld/ELF/InputFiles.cpp
  lld/test/ELF/lto/comdat-noduplicates.ll
  lld/wasm/InputFiles.cpp
  llvm/include/llvm/LTO/LTO.h
  llvm/include/llvm/Object/IRSymtab.h
  llvm/lib/Object/IRSymtab.cpp
  llvm/test/LTO/Resolution/X86/symtab.ll
  llvm/test/Object/X86/irsymtab.ll
  llvm/tools/gold/gold-plugin.cpp
  llvm/tools/llvm-lto2/llvm-lto2.cpp

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