[clang] [llvm] Adding splitdouble HLSL function (PR #109331)

[Chris B via llvm-commits]

https://github.com/llvm-beanz commented:

I've got a lot of style nits here.

In general it is nice to break up changes into smaller changes where you can. One obvious split in this PR would have been to put the DirectX backend changes in first in a separate PR.

Smaller PRs are easier to review because they take smaller blocks of time from a reviewer.

https://github.com/llvm/llvm-project/pull/109331