[PATCH] D26438: [Verifier] Add verification for TBAA metadata

[Manman Ren via llvm-commits]

manmanren added a comment.

In https://reviews.llvm.org/D26438#591405, @sanjoy wrote:

> In https://reviews.llvm.org/D26438#591400, @manmanren wrote:
>
> > In https://reviews.llvm.org/D26438#591227, @sanjoy wrote:
> >
> > > In https://reviews.llvm.org/D26438#591194, @mehdi_amini wrote:
> > >
> > > > When did we stop using the "old" form? We don't need to preserve an auto-upgrade forever, as long as we can simply drop metadata for old bitcodes this is as valid alternative.
> > >
> > >
> > > We've had the auto upgrade logic for what looks like approximately 3 years.  I think it is reasonable to deprecate the functionality and eventually remove it, though I know (from off-list emails) that it will break (in terms of performance, not correctness) downstream users.
> >
> >
> > Can you explain more on why it will break downstream users in terms of performance?
>
>
> I meant if we go by Mehdi's strategy of dropping old style tbaa metadata instead of auto-upgrading them then downstream users who generate the old style tbaa metadata will no longer get the benefit of TBAA.  Their code will be correctly compiled, but will run slower.


Got it!


https://reviews.llvm.org/D26438