[PATCH] D114112: [SCEVAA] Avoid forming malformed pointer diff expressions

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

In D114112#3138447 <https://reviews.llvm.org/D114112#3138447>, @reames wrote:

> In D114112#3138430 <https://reviews.llvm.org/D114112#3138430>, @efriedma wrote:
>
>> Do we have some documentation that indicates what we expect alias() to return in the case where instructionCouldExistWitthOperands fails?
>
> Not quite sure what you're asking.  If we have two pointers, the conservative result should always be MayAlias.  Is that what you meant?

I mean, if we do an alias query with a pair of Instruction* that don't have a common scope, are all AA implementations required to always return MayAlias?  Call llvm_unreachable?  Or can we perform some sort of approximation of the possible values produced by the Instruction? If we do approximate the value, what are the rules for that?


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