[Bug tree-optimization/51315] [4.6/4.7 regression] unaligned memory accesses generated with -ftree-sra

["ebotcazou at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51315

--- Comment #8 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-12-06 16:41:38 UTC ---
> Note that in the end it's always us transforming
> 
>  a->b.c
> 
> to (effectively)
> 
>  T *tem = &a->b.c;
>  *tem
> 
> which expand unfortunately handles differently.  So whenever we do that
> we have to either avoid doing that if expand would have a different
> idea about the results alignment (there is currently no way that computes
> just expands idea of an expressions alignment - one piece of a good
> solution would provide that, not only SRA has this "issue"), or, stick
> that information somewhere

AFAICS that's what the memcpy folder does if STRICT_ALIGNMENT, so the generated
GIMPLE is perfectly valid.   But SRA isn't as cautious as the folder and, in
particular, doesn't compare the alignments of source and destination.  In any
case, I don't think that we want to patch outside SRA on the 4.6 branch.