[llvm] [SimplifyCFG] Treat umul + extract pattern as cheap single instruction. (PR #124933)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw approved this pull request.

LGTM. Thank you! Can you adjust the PR description to make it ready for merge?
Please wait for additional approval from other reviewers :)

https://github.com/llvm/llvm-project/pull/124933