[llvm] [InstCombine] Fold scmp(X, 0) to sext_or_trunc(X) when X is in [-1, 1] (PR #216046)

[via llvm-commits]

scottmcm wrote:

I suppose it's possible that this isn't triggering because of the same phase ordering problem as #52701 -- it comes not from Rust emitting `[su]cmp` directly, but it emitting `memcmp` calls that are turned into this too late in the pipeline for this to trigger.

https://github.com/llvm/llvm-project/pull/216046