[llvm] [AA][ScopedNoAliasAA] Returns ModRef when an alias exists (PR #70159)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

It's sufficient to have !noalias on one instruction and !alias.scope on the other. You don't need both of them to have !noalias and !alias.scope.

See https://llvm.org/docs/LangRef.html#noalias-and-alias-scope-metadata for documentation and in particular:

> When evaluating an aliasing query, if for some domain, the set of scopes with that domain in one instruction’s alias.scope list is a subset of (or equal to) the set of scopes for that domain in another instruction’s noalias list, then the two memory accesses are assumed not to alias.

https://github.com/llvm/llvm-project/pull/70159