[all-commits] [llvm/llvm-project] 067a11: RegisterCoalescer: Do not introduce uses of empty ...

[Matt Arsenault via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 067a11015d54bb8822601f7d242e4f8a0c7c5a7d
      https://github.com/llvm/llvm-project/commit/067a11015d54bb8822601f7d242e4f8a0c7c5a7d
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2025-10-10 (Fri, 10 Oct 2025)

  Changed paths:
    M llvm/lib/CodeGen/RegisterCoalescer.cpp
    A llvm/test/CodeGen/AMDGPU/coalescer-avoid-coalesce-class-with-no-registers.ll
    A llvm/test/CodeGen/AMDGPU/coalescer-avoid-coalesce-class-with-no-registers.mir

  Log Message:
  -----------
  RegisterCoalescer: Do not introduce uses of empty register classes (#161809)

Check RegisterClassInfo if any registers of the new class are
actually available for use. Currently AMDGPU overrides shouldCoalesce
to avoid this situation. The target hook does not have access to the
dynamic register class counts, but ideally the target hook would
only be used for profitability concerns.

The new test doesn't change, due to the AMDGPU shouldCoalesce override,
but would be unallocatable if we dropped the override and switched
to the default implementation. The existing limit-coalesce.mir already
tests the behavior of this override, but it's too conservative and
isn't checking the case where the new class is unallocatable. Add
this check so it can be relaxed.



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