RFA (fold): PATCH for c++/49290 (folding *(T*)(ar+10))

[Jakub Jelinek]

On Tue, Jun 07, 2011 at 12:19:59PM +0200, Richard Guenther wrote:
> On Tue, Jun 7, 2011 at 7:39 AM, Jason Merrill <jason@redhat.com> wrote:
> > In the testcase, fold_indirect_ref_1 won't fold *(T*)(s1+10) to an ARRAY_REF
> > because T != unsigned. Â Even if it were just a typedef to unsigned, that
> > isn't close enough, but in this case it's a typedef to const unsigned.
> >
> > I'm not sure what the type coherence rules are for ARRAY_REF. Â Is it really
> > necessary that the type of the ARRAY_REF match exactly the element type of
> > the array?
> 
> I _think_ that you can unconditionally change the code to do
> 
>   TYPE_MAIN_VARIANT (t1) == TYPE_MAIN_VARIANT (t2)
>   && TYPE_QUALS (t1) == TYPE_QUALS (t2)
> 
> now, I'm not sure if for the testcase T and unsigned differ in qualifiers.

I guess folding into array_ref that way is fine, but you should in the end
fold_convert_loc it to the expected type, while the middle-end has the
notion of useless type conversions, fold-const.c is also used by FEs and
I think it is expected to have the types exactly matching.
So (T)s1[10] instead of s1[10] in this case.

	Jakub