[all-commits] [llvm/llvm-project] 15482c: [ElimAvailExtern] Add an option to allow to conver...

[Shilei Tian via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 15482c83aa2b05779d7ad947c34835656ab9da1c
      https://github.com/llvm/llvm-project/commit/15482c83aa2b05779d7ad947c34835656ab9da1c
  Author: Shilei Tian <i at tianshilei.me>
  Date:   2025-06-17 (Tue, 17 Jun 2025)

  Changed paths:
    M llvm/lib/Transforms/IPO/ElimAvailExtern.cpp
    A llvm/test/Transforms/EliminateAvailableExternally/convert-global-variables-to-local.ll

  Log Message:
  -----------
  [ElimAvailExtern] Add an option to allow to convert global variables in a specified address space to local (#144287)

Currently, the `EliminateAvailableExternallyPass` only converts certain
available externally functions to local if `avail-extern-to-local` is
set or in
contextual profiling mode. For global variables, it only drops their
initializers.

This PR adds an option to allow the pass to convert global variables in
a
specified address space to local. The motivation for this change is to
correctly
support lowering of LDS variables (`__shared__` variables, in more
generic
terminology) when ThinLTO is enabled for AMDGPU.

A `__shared__` variable is lowered to a hidden global variable in a
particular
address space by the frontend, which is roughly same as a `static` local
variable. To properly lower it in the backend, the compiler needs to
check all
its uses. Enabling ThinLTO currently breaks this when a function
containing a
`__shared__` variable is imported from another module. Even though the
global
variable is imported along with its associated function, and the
function is
privatized by the `EliminateAvailableExternallyPass`, the global
variable itself
is not.

It's safe to privatize such global variables, because they're _local_ to
their
associated functions. If the function itself is privatized, its
associated
global variables should also be privatized accordingly.



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