[PATCH] D120083: [instsimplify] Generalize offset handling when compare pointers derived from allocas

[Augie Fackler via Phabricator via llvm-commits]

durin42 added a comment.

In D120083#3330734 <https://reviews.llvm.org/D120083#3330734>, @nikic wrote:

>> I vaguely think there should be a more concise way to write these checks. Anyone see one?
>
> As we're dealing with equality comparisons here, we can subtract a common offset from both sides. So rather than dealing with `LHS + LHSOffset == RHS + RHSOffset`, we can instead deal with `LHS + Offset == RHS`, where `Offset = LHSOffset - RHSOffset`. We should be able to fold that if and only if `Offset > -MinSize(RHS)` and `Offset < MinSize(LHS)`.
>
> Does that sound about right?

It took some work to convince myself, but I think that's right.


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https://reviews.llvm.org/D120083