[llvm] AMDGPU: Handle legal v2bf16 atomicrmw fadd for gfx12 (PR #95930)

[Matt Arsenault via llvm-commits]

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@@ -743,6 +743,12 @@ def FeatureAtomicGlobalPkAddBF16Inst : SubtargetFeature<"atomic-global-pk-add-bf
  [FeatureFlatGlobalInsts]
 >;
 
+def FeatureAtomicBufferPkAddBF16Inst : SubtargetFeature<"atomic-buffer-pk-add-bf16-inst",
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arsenm wrote:

This doesn't exist downstream 

https://github.com/llvm/llvm-project/pull/95930