[all-commits] [llvm/llvm-project] b60c11: MachineUniformityAnalysis: Improve isConstantOrUnd...

[Petar Avramovic via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b60c118f53e6f7e5328e54dc26b4d6787030c02b
      https://github.com/llvm/llvm-project/commit/b60c118f53e6f7e5328e54dc26b4d6787030c02b
  Author: Petar Avramovic <Petar.Avramovic at amd.com>
  Date:   2025-01-24 (Fri, 24 Jan 2025)

  Changed paths:
    M llvm/lib/CodeGen/MachineSSAContext.cpp
    M llvm/test/Analysis/UniformityAnalysis/AMDGPU/MIR/hidden-diverge-gmir.mir
    M llvm/test/Analysis/UniformityAnalysis/AMDGPU/MIR/hidden-loop-diverge.mir
    M llvm/test/Analysis/UniformityAnalysis/AMDGPU/MIR/uses-value-from-cycle.mir
    M llvm/test/CodeGen/AMDGPU/GlobalISel/divergence-structurizer.mir
    M llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-mui-regbanklegalize.mir
    M llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-mui-regbankselect.mir
    M llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-mui.ll
    M llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-mui.mir

  Log Message:
  -----------
  MachineUniformityAnalysis: Improve isConstantOrUndefValuePhi (#112866)

Change existing code for G_PHI to match what LLVM-IR version is doing
via PHINode::hasConstantOrUndefValue. This is not safe for regular PHI
since it may appear with an undef operand and getVRegDef can fail.
Most notably this improves number of values that can be allocated
to sgpr in AMDGPURegBankSelect.
Common case here are phis that appear in structurize-cfg lowering
for cycles with multiple exits:
Undef incoming value is coming from block that reached cycle exit
condition, if other incoming is uniform keep the phi uniform despite
the fact it is joining values from pair of blocks that are entered
via divergent condition branch.



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