[llvm] [InstCombine] Optimize icmp(sub(a, c), sub(b, c)) to icmp(a, b) if a, b, and c are pointers (PR #161698)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> Alive proof has some issues with undef that I don't quite understand, https://alive2.llvm.org/ce/z/AdZoWJ
Particularly %p2 = ptrtoint ptr %2 to i2 is solved different, in Src, i2 %p2 = #x3 (3, -1), while in Tgt: i2 %p2 = #x0 (0)

Each use of undef can observe a different value. See https://llvm.org/docs/UndefinedBehavior.html#undef-values
You can pass `--disable-undef-input` to Alive2.


https://github.com/llvm/llvm-project/pull/161698