[llvm] [GlobalISel][AArch64] Legalize G_FABS and G_FNEG for SVE (PR #114784)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

```
SDValue AArch64TargetLowering::LowerToPredicatedOp(SDValue Op,
                                                   SelectionDAG &DAG,
                                                   unsigned NewOp) const {

...
  if (isMergePassthruOpcode(NewOp))
      Operands.push_back(DAG.getUNDEF(ContainerVT));


}
```
Apparently the DAG also uses Undef for merge passthrough.



https://github.com/llvm/llvm-project/pull/114784