[llvm] [AArch64][SVE] Lower scalar FP converts to SVE when Neon is unavailable (PR #112564)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

> There was some discussion on that here [#112564 (comment)](https://github.com/llvm/llvm-project/pull/112564#discussion_r1803497212), originally this followed the neon combine that matched `(from_int (to_int))` -- [564d9a7](https://github.com/llvm/llvm-project/commit/564d9a78713e1f95dbef6a14441b82d77c25f04d), but it was suggested to make it into a more generally applied lowering.

I agree with the sentiments, this isn't a selection problem either, but not the new home of the transformation.  DAGCombine is the place to optimise the DAG whereas LowerOperation exists to legalise the DAG.  I'm happy to be convinced otherwise but given there is nothing illegal about the DAG to me that suggests a DAGCombine.

https://github.com/llvm/llvm-project/pull/112564