[llvm-commits] [pr12979][patch/rfc] Clear nsw/nuw in gvn

[Nuno Lopes]

>> Metadata nodes are uniqued. When merging two files of the same language, 
>> the
>> type trees will merge as well, and they will then share the same root and
>> potentially many sub-trees as well.
> Okay
>
>> So I believe the reasoning I presented is correct.
>
> Oh, i don't disagree that least common ancestor is correct, it's what
> we do in GCC.  I'm just pointing out the semantic you are suggesting
> (loads in two different tbaa trees don't alias) is exactly the
> opposite of what the semantic the language guide says :)
>
> So if we want to go with that, we should update the language guide to
> state that we don't consider things from two different tbaa trees to
> alias.

Actually the documentation is correct regarding the implementation. (I just 
checked the TBAA code).
Dan: is there any reason why pointers with different type roots are 
considered that they may alias?  It probably doesn't happen often anyway..

Nuno