[llvm] [AArch64] canCreateUndefOrPoisonForTargetNode - AArch64ISD::VASHR\VLSHR\VSHL can't create undef/poison (PR #156445)

[David Green via llvm-commits]

davemgreen wrote:

> DAG.visitFREEZE will call canCreateUndefOrPoison with ConsiderFlags=false, which means it ignores the Exact flag. If it succeeds in pushing the FREEZE through it will create a new VASHR node but without the Exact flag. Its a hack but we could always treat ConsiderFlags=true for these node and fail if they have the Exact flag.

Does that mean it should be `return ConsiderFlags ? Op.hasExact() : false;`?

https://github.com/llvm/llvm-project/pull/156445