[all-commits] [llvm/llvm-project] 87c43f: [InstrProfiling] Delete linkage/visibility togglin...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 87c43f3aa99d778755c7f5420e955885f855ecad
      https://github.com/llvm/llvm-project/commit/87c43f3aa99d778755c7f5420e955885f855ecad
  Author: Fangrui Song <i at maskray.me>
  Date:   2021-06-02 (Wed, 02 Jun 2021)

  Changed paths:
    M compiler-rt/test/profile/Windows/coverage-weak-lld.cpp
    M llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
    M llvm/test/Instrumentation/InstrProfiling/linkage.ll
    M llvm/test/Instrumentation/InstrProfiling/platform.ll
    M llvm/test/Instrumentation/InstrProfiling/profiling.ll

  Log Message:
  -----------
  [InstrProfiling] Delete linkage/visibility toggling for Windows

The linkage/visibility of `__profn_*` variables are derived
from the profiled functions.

    extern_weak => linkonce
    available_externally => linkonce_odr
    internal => private
    extern => private
    _ => unchanged

The linkage/visibility of `__profc_*`/`__profd_*` variables are derived from
`__profn_*` with linkage/visibility wrestling for Windows.

The changes can be folded to the following without changing semantics.

```
if (TT.isOSBinFormatCOFF() && !NeedComdat) {
  Linkage = GlobalValue::InternalLinkage;
  Visibility = GlobalValue::DefaultVisibility;
}
```

That said, I think we can just delete the code block.

An extern/internal function will now use private `__profc_*`/`__profd_*`
variables, instead of internal ones. This saves some symbol table entries.

A non-comdat {linkonce,weak}_odr function will now use hidden external
`__profc_*`/`__profd_*` variables instead of internal ones.  There is potential
object file size increase because such symbols need `/INCLUDE:` directives.
However such non-comdat functions are rare (note that non-comdat weak
definitions don't prevent duplicate definition error).

The behavior changes match ELF.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D103355