[all-commits] [llvm/llvm-project] ba6c8d: [AMDGPU] Combine DPP mov even if old reg def is in...

Jay Foad via All-commits all-commits at lists.llvm.org
Thu May 5 03:34:06 PDT 2022

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: ba6c8d42d4dce8776450effe4675c3264b7481dd
  Author: Jay Foad <jay.foad at amd.com>
  Date:   2022-05-05 (Thu, 05 May 2022)

  Changed paths:
    M llvm/lib/Target/AMDGPU/GCNDPPCombine.cpp
    M llvm/test/CodeGen/AMDGPU/dpp_combine.mir

  Log Message:
  [AMDGPU] Combine DPP mov even if old reg def is in different BB

Given a DPP mov like this:

  %2:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
  %3:vgpr_32 = V_MOV_B32_dpp %2, %1, 1, 1, 1, 0, implicit $exec

this patch just removes a check that %2 (the "old reg") was defined in
the same BB as the DPP mov instruction. GCNDPPCombine requires that the
MIR is in SSA form so I don't understand why the BB matters.

This lets the optimization work in more real world cases when the
definition of %2 gets hoisted out of a loop.

Differential Revision: https://reviews.llvm.org/D124182

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