[all-commits] [llvm/llvm-project] 6e5cbc: "Reland "[pgo] Avoid introducing relocations by us...

[Paul Kirth via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6e5cbc097a5ac7fa95a8f425af8b03958151c763
      https://github.com/llvm/llvm-project/commit/6e5cbc097a5ac7fa95a8f425af8b03958151c763
  Author: Paul Kirth <paulkirth at google.com>
  Date:   2023-01-11 (Wed, 11 Jan 2023)

  Changed paths:
    A compiler-rt/test/profile/instrprof-discarded-comdat.cpp
    M llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
    M llvm/test/Transforms/PGOProfile/comdat.ll
    A llvm/test/Transforms/PGOProfile/prof_avoid_relocs.ll

  Log Message:
  -----------
  "Reland "[pgo] Avoid introducing relocations by using private alias"

In many cases, we can use an alias to avoid a symbolic relocations,
instead of using the public, interposable symbol. When the instrumented
function is in a COMDAT, we can use a hidden alias, and still avoid
references to discarded sections.

Previous versions of this patch allowed the compiler to name the
generated alias, but that would only be valid when the functions were
local. Since the alias may be used across TUs we use a more
deterministic naming convention, and add a .local suffix to the alias
name just as we do for relative vtables aliases.

This should be safe to land after an incorrect LLD assertion was removed
in https://reviews.llvm.org/rG20894a478da224bdd69c91a22a5175b28bc08ed9
which caused assertion failures in LLD on Mac.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D137982