[llvm] Reland: Port Swift's merge function pass to llvm: merging functions that differ in constants (PR #71584)

[Manman Ren via llvm-commits]

manman-ren wrote:

> Just some quick drive-by comments, it's unlikely that I will be able to review in detail anytime soon.

Thanks for the quick feedback. If you don't have bandwidth to review anytime soon, any reviewers that you can suggest to make sure this is adequately reviewed?

Thanks!

https://github.com/llvm/llvm-project/pull/71584