[llvm] [InstCombine] Make indexed compare fold GEP source type independent (PR #71663)

[Nikita Popov via llvm-commits]

nikic wrote:

@dtcxzyw I'm not seeing something exactly like that (using usub.sat) in my own IR diffs, but I do see something quite similar in pcmul.c.ll (https://gist.github.com/nikic/805ec1c7a79b8a94ff6c1a60a4a19d3e). As far as I can tell, what happens there is that a loop that stores 0 gets converted into a memset by LIR now. Nominally this is a positive change, but it can also be negative if the number of stores is actually low (as the trip count calculation is complex).

https://github.com/llvm/llvm-project/pull/71663