[PATCH] D146701: [AMDGPU] Create Subtarget Features for some of 16 bits atomic fadd instructions

Thu Mar 23 12:59:22 PDT 2023

mariusz-sikora-at-amd added inline comments.

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Comment at: llvm/lib/Target/AMDGPU/FLATInstructions.td:1915

+defm GLOBAL_ATOMIC_PK_ADD_F16 : FLAT_Global_Real_Atomics_vi <0x04e, 0>;
+defm GLOBAL_ATOMIC_PK_ADD_BF16 : FLAT_Global_Real_Atomics_vi<0x52>;
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foad wrote:
> mariusz-sikora-at-amd wrote:
> > foad wrote:
> > > Are these changes (from here to the end of the file) still required?
> > Not sure if I understand what you mean. Could you please elaborate more ? Are you referring to the fact that both flat_atomic and global_atomic have FLAT encoding and could be unified ?
> > I thought this is required, but now you got me thinking ...
> I don't understand why the changes from here to the end of the file are required. It looks like you have just moved some definitions around, so that they no longer have a SubtargetPredicate applied. Is that correct? Why?
Yes, I moved them out from under the SubtargetPredicates. All tests are passing. Even 'negative' for unsupported generations, but after deeper looking into 'gen-instr-info' from TableGen I see that there is a difference for GLOBAL_ATOMIC_PK_ADD_F16_*_vi definitions of Real Instructions.

1) I'm still convinced that SubtargetPredicate = isGFX940Plus is not needed for definitions which inherit from FLAT_Global_Real_Atomics_gfx940. Multiclass sets AssemblerPredicate = isGFX940Plus and when looking how Predicates list is created we can see that AssemblerPredicate is used in creation of final list of Predicates.

  list<Predicate> Predicates = PredConcat<
                                 PredConcat<PredConcat<OtherPredicates,
                                                       SubtargetPredicate>.ret,
                                            AssemblerPredicate>.ret,
                                 WaveSizePredicate>.ret;

2) In case of FLAT_Global_Real_Atomics_vi I see that SubtargetPredicate = isGFX8GFX9NotGFX940 will be required, because AssemblerPredicate is isGFX8GFX9;
I wonder why everything works event when not having these SubtargetPredicates = isGFX8GFX9NotGFX940

I will revert these changes and move definitions back under the SubtargetPredicates. 

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D146701/new/

https://reviews.llvm.org/D146701