[llvm] [AArch64][SDAG] Lower f16->s16 FP_TO_INT_SAT to *v1f16 (PR #154822)

[Kajetan Puchalski via llvm-commits]

mrkajetanp wrote:

It feels like there should be a better way to do this, but SDAG was really unhappy with me trying to do anything that involved having an `i16` type on any operation, so this was the only way I've found (so far) of having it not crash.

https://github.com/llvm/llvm-project/pull/154822