[llvm] [AArch64][CodeGen] Fix crash when fptrunc returns fp16 with +nofp attr (PR #81724)

[David Green via llvm-commits]

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@@ -25008,6 +25008,16 @@ void AArch64TargetLowering::ReplaceNodeResults(
       Results.push_back(
           LowerToPredicatedOp(SDValue(N, 0), DAG, AArch64ISD::MULHU_PRED));
     return;
+  case ISD::FP_ROUND: {
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davemgreen wrote:

It is.. a very old bit of the code that probably would be better if it worked differently. But I'm not sure if it's easy to change.

I believe it comes from AArch64TargetLowering::LowerBITCAST? Could that function behave differently, or could the ISD::BITCAST be not marked Custom with no-fp?

https://github.com/llvm/llvm-project/pull/81724