Re: [PATCH] c-family: Improve MEM_REF printing for diagnostics [PR98597]

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Jan 14, 2021 at 11:05:40AM +0100, Richard Biener wrote:
> > > Could we print
> > > t.u.b
> > > if the TBAA type is compatible with the type of the reference and perhaps
> > > *(int*)&t.u.b
> > > if it is incompatible?
> > > >From the aliasing perspective that is still different, but we don't print
> > > the TBAA type anyway.
> 
> True.  As said we could simply add a GCC extension to write a MEM_REF
> in source and print that syntax ... then it would be valid (GCC) C/C++.

But even if we do that unless people are familiar with that extension they
wouldn't know what it means (and they didn't write it in that way in their
source).

> > There is another option I forgot about, but perhaps it is too verbose.
> > Print
> > *(int*)((char*)&t + offsetof (struct T, u.b))
> 
> or rather offsetof (struct T, u) to not single out a specific union
> member?

Sure, I can just get rid of the UNION_TYPE handling from the function,
or use it only if the TBAA access type is compatible.

	Jakub