[PATCH] D134354: [AMDGPU][GlobalISel] Support mad/fma_mix selection

Wed Oct 19 02:26:56 PDT 2022

foad added inline comments.

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Comment at: llvm/lib/Target/AMDGPU/AMDGPUGISel.td:156

+def gi_vop3_mad_mix_mods :
+    GIComplexOperandMatcher<s64, "selectVOP3PMadMixMods">,
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Pierre-vh wrote:
> foad wrote:
> > Pierre-vh wrote:
> > > foad wrote:
> > > > Is this required? I am confused about whether you are now matching VOP3PMadMixMods in TableGen patterns, or only doing it from the C++ code in selectG_FMA.
> > > I'm doing it exclusively in C++.
> > > This is needed to tell the GlobalISelEmitter that, when it sees "VOP3PMadMixMods" it needs to use the "selectVOP3PMadMixMods" function from AMDGPUInstructionSelector.
> > > Without that, it wouldn't import patterns that use it.
> > I'm still confused. If we are now importing patterns that use VOP3PMadMixMods, why do you need to do the selection in C++ code?
> It's a ComplexPattern
> ```
> def VOP3PMadMixMods  : ComplexPattern<untyped, 2, "SelectVOP3PMadMixMods">;
> ```
> Those functions work with DAG nodes and must be rewritten for GISel so the patterns can be imported
> https://llvm.org/docs/GlobalISel/InstructionSelect.html#complexpatterns
Right, but why do you need to write code in selectG_FMA_FMAD to manually select MAD_MIX/FMA_MIX? Why can't the imported patterns do this automatically?

Repository:
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  https://reviews.llvm.org/D134354/new/

https://reviews.llvm.org/D134354