r281277 - [Sema] Fix PR30346: relax __builtin_object_size checks.

[Joerg Sonnenberger via cfe-commits]

On Tue, Sep 13, 2016 at 12:51:52PM -0700, Richard Smith wrote:
> On Tue, Sep 13, 2016 at 10:44 AM, Joerg Sonnenberger via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
> 
> > IMO this should be restricted to code that explicitly disables C/C++
> > aliasing rules.
> 
> 
> Do you mean -fno-strict-aliasing or -fno-struct-path-tbaa or something else
> here? (I think we're not doing anyone any favours by making _FORTIFY_SOURCE
> say that a pattern is OK in cases when LLVM will in fact optimize on the
> assumption that it's UB, but I don't recall how aggressive
> -fstruct-path-tbaa is for trailing array members.)

The former immediately, the latter potentially as well. I can't think of
many use cases for this kind of idiom that don't involve type prunning
and socket code is notoriously bad in that regard by necessity.

Joerg