[llvm] [AMDGPU] Form V_MAD_U64_U32 from mul24/mulhi24 (PR #72393)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Also I still don't understand the deal with the speed model. Should it affect ISel patterns really?

Yes, I think so. The job of isel (including pattern-based isel) is to pick the "best" instructions according to some cost model, either performance or code size, so certainly changes in the cost model should affect which isel patterns are used.

https://github.com/llvm/llvm-project/pull/72393