Re: [PATCH] Use sufficient alignment when expanding VCE (PR target/35366)

["Richard Guenther" <richard dot guenther at gmail dot com>]

On Tue, Nov 11, 2008 at 12:40 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Nov 11, 2008 at 09:40:16AM -0600, Richard Guenther wrote:
>> On Tue, Nov 11, 2008 at 7:30 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>> > This is another patch for PR35366, either of the patches fixes the failure,
>> > but IMHO we want both.  If for whatever reason VIEW_CONVERT_EXPR <double, STRING_CST>
>> > (or some other VCE) isn't folded, and the TREE_TYPE of the VCE needs bigger
>> > alignment than the inner operand, the inner constant is emitted with a small
>> > alignment, but it is actually accessed as if the alignment was big enough
>> > for the outer type.  The following patch makes sure an inner constant
>> > is sufficiently aligned.
>> >
>> > Ok for trunk?
>>
>> Is it always possible to force the alignment of the inner object?  I think
>
> For constants yes (that's why I use CONSTANT_CLASS_P), otherwise no.
>
>> the same problem may exist for V_C_E <double> (*p) when we cannot
>> influence the alignment of *p.  So shouldn't we make sure to have the
>> correct MEM_ALIGN instead?  Or does it work in that case already?
>
> If you have an unaligned pointer and V_C_E <double> (*p), then
> MEM_ALIGN will be correct I believe (at least, without this patch
> it is A8 for LC2, matching its alignment).  Of course whether it
> works or not depends on whether the target requires strict alignment
> or not, but I'd say if it does and the pointer isn't aligned, it was
> a programmer's bug.
> V_C_E of a constant is something that is generated by the compiler itself
> and is something we can align sufficiently, so we IMHO should.

Ok.  The patch is ok then.

Thanks,
Richard.


>        Jakub
>