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

Richard Guenther richard.guenther@gmail.com
Tue Jun 7 12:03:00 GMT 2011

On Tue, Jun 7, 2011 at 12:27 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> 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.  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.  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_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.

I'm not sure that's a good idea if the caller wants an lvalue.


>        Jakub

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