[llvm] [NVPTX] Select bfloat16 add/mul/sub as fma on SM80 (PR #121065)

[via llvm-commits]

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@@ -853,6 +853,16 @@ NVPTXTargetLowering::NVPTXTargetLowering(const NVPTXTargetMachine &TM,
       AddPromotedToType(Op, MVT::bf16, MVT::f32);
   }
 
+  // Lower bf16 add/mul/sub as fma when it avoids promotion
+  for (const auto &Op : {ISD::FADD, ISD::FMUL, ISD::FSUB}) {
+    for (const auto &VT : {MVT::bf16, MVT::v2bf16}) {
+      if (getOperationAction(Op, VT) != Legal &&
+          getOperationAction(ISD::FMA, VT) == Legal) {
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peterbell10 wrote:

`setBF16OperationAction` only allows two variants, supported or unsupported. So we can't set custom for an in-between range.

https://github.com/llvm/llvm-project/pull/121065