[PATCH] D97649: [InstrProfiling] Place __llvm_prf_vnodes and __llvm_prf_names in llvm.used on ELF

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: davidxl, phosek.
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Herald added subscribers: llvm-commits, Sanitizers.

`__llvm_prf_vnodes` and `__llvm_prf_names` are used by runtime but not
referenced via relocation in the translation unit.

With `-z start-stop-gc` (D96914 <https://reviews.llvm.org/D96914> https://sourceware.org/bugzilla/show_bug.cgi?id=27451),
the linker does not let `__start_/__stop_` references retain them.

Place `__llvm_prf_vnodes` and `__llvm_prf_names` in `llvm.used` to make
them retained by the linker.

This patch changes most existing `UsedVars` cases to `CompilerUsedVars`
to reflect the ideal state - if the binary format properly supports
section based GC (dead stripping), `llvm.compiler.used` should be sufficient.

`__llvm_prf_vnodes` and `__llvm_prf_names` are switched to `UsedVars`
since we want them to be unconditionally retained by both compiler and linker.

Behaviors on other COFF/Mach-O are not affected.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97649

Files:
  compiler-rt/test/profile/Linux/instrprof-value-merge.c
  llvm/include/llvm/Transforms/Instrumentation/InstrProfiling.h
  llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
  llvm/test/Instrumentation/InstrProfiling/icall.ll

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