[PATCH] D97665: [InstSimplify] Don't fold comparisons of non-inbounds GEPs

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

> I don't have a clear model for the semantics of pointer comparison ATM; Pointer comparison *sometimes* needs to take provenance into consideration because LLVM folds p1 == p2 where p1 and p2 are pointing to two different zero-size objects having the same address into false.
> Also, considering provenance into account allows aggressively folding pointer comparisons. It isn't clear how *frequently* the provenance should be considered.

FWIW, these are a few examples and relevant links:

- A ptr comparison folding to false regardless of addresses of two possibly overlapping stack allocations: https://godbolt.org/z/ok4vFJ , bugzilla report: https://bugs.llvm.org/show_bug.cgi?id=44342
- Another example: https://godbolt.org/z/bhrsK1 (well it wasn't a zero-size object, but simply merging two identical global objects. Anyway it shows that defining ptr comparison is something non-trivial), reduced from: https://bugs.llvm.org/show_bug.cgi?id=47090 , https://github.com/rust-lang/rust/issues/73722


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