[compiler-rt] [llvm] [SelectionDAG] Add `STRICT_BF16_TO_FP` and `STRICT_FP_TO_BF16` (PR #80056)

[Phoebe Wang via llvm-commits]

================
@@ -437,6 +437,13 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(Op, MVT::f128, Expand);
   }
 
+  // FIXME: If a target has F16C, it needs to be Custom.
+  setOperationAction(ISD::STRICT_FP_TO_BF16, MVT::f32, Expand);
----------------
phoebewang wrote:

I think we don't need to exclude `f80` and `f128`. We can use a loop for them.
```
for (auto VT : {MVT::f32, MVT::f64, MVT::f80, MVT::f128}) {
  setOperationAction(ISD::STRICT_FP_TO_BF16, VT, Expand);
  setOperationAction(ISD::STRICT_BF16_TO_FP, VT, Expand);
}
```

https://github.com/llvm/llvm-project/pull/80056