On Tue, Nov 12, 2013 at 10:53 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> On Tue, Nov 12, 2013 at 01:42:00PM -0800, Mike Stump wrote:
>> On Nov 12, 2013, at 1:16 PM, Jakub Jelinek <ja...@redhat.com> wrote:
>> > On Tue, Nov 12, 2013 at 01:11:04PM -0800, Mike Stump wrote:
>> >> Alignments are stored in a byte, large alignments don't actually work
>> >> nicely. This caps the alignment to 128, as most ports would define
>> >> BIGGEST_ALIGNMENT to be smaller than this. The competing change would to
>> >> be to make it a short, but, I'd be happy to punt that until such time as
>> >> someone actually needs that.
>> >>
>> >> Ports break down this way currently:
>> >>
>> >> 12 #define BIGGEST_ALIGNMENT 64
>> >> 10 #define BIGGEST_ALIGNMENT 32
>> >> 6 #define BIGGEST_ALIGNMENT 128
>> >> 3 #define BIGGEST_ALIGNMENT 8
>> >> 8 #define BIGGEST_ALIGNMENT 16
>> >
>> > You are missing i386 that has BIGGEST_ALIGNMENT 512 (or less, depending on
>> > compiler options). So this doesn't look right.
>>
>> And yet alignments for modes with sizes like 256 won't work and i386 has no
>> mode with alignment bigger than 128 in this table.
>
> Well, BIGGEST_ALIGNMENT is in bits, while mode_base_align seems to be in
> bytes it
> seems:
>
> unsigned int
> get_mode_alignment (enum machine_mode mode)
> {
> return MIN (BIGGEST_ALIGNMENT, MAX (1,
> mode_base_align[mode]*BITS_PER_UNIT));
> }
>
> So, supposedly it works up to 1024 bit alignment right now.
Either storing log2 (alignment) in mode_base_align or increasing its
size is possible if required. IIRC we store alignment log2 elsewhere.
Richard.
> Jakub
