[llvm] [InstCombine] Fold `(icmp pred (trunc nuw/nsw X), C)` -> `(icmp pred X, (zext/sext C))` (PR #87935)

[John Regehr via llvm-commits]

regehr wrote:

> IIRC @regehr is developing a fuzzer that mutates existing instcombine tests :)

it is my student Yuyou who has written this, but I have had a hand in it, and I use it often. if anyone else wants to run it, build this branch of Alive2:

https://github.com/Hatsunespica/alive2/tree/mutate

it can be used as a standalone mutator, but also it can generate a mutant and analyze it using Alive2 without forking, which makes it very fast. I'm mostly fuzzing the AArch64 backend these days, so if anyone wants to do middle-end fuzzing, that would be good!

https://github.com/llvm/llvm-project/pull/87935