On 11/06/12 15:17, Richard Guenther wrote:
> On Mon, Jun 11, 2012 at 3:16 PM, Richard Earnshaw <rearn...@arm.com> wrote:
>> The ARM ABI states that vectors larger than 64 bits in size still have
>> 64-bit alignment; never-the-less, the HW supports alignment hints of up
>> to 128-bits in some cases and will trap in a vector has an alignment
>> that less than the hint. GCC currently hard-codes larger vectors to be
>> aligned by the size of the vector, which means that 128-bit vectors are
>> marked as being 128-bit aligned.
>>
>> The ARM ABI unfortunately does not support generating such alignment for
>> parameters passed by value and this can lead to traps at run time. It
>> seems that the best way to solve this problem is to allow the back-end
>> to set an upper limit on the alignment permitted for a vector.
>>
>> I've implemented this as a separate hook, rather than using the existing
>> hooks because there's a strong likelihood of breaking some existing ABIs
>> if I did it another way.
>>
>> There are a couple of tests that will need some re-working before this
>> can be committed to deal with the fall-out of making this change; I'll
>> prepare those changes if this patch is deemed generally acceptable.
>
> Hm. Where would you use that target hook?
>
Doh!
It was supposed to be in the patch set... :-(
in layout_type(), where the alignment of a vector is forced to the size
of the vector.
R.
--- stor-layout.c (revision 188348)
+++ stor-layout.c (local)
@@ -2131,9 +2131,11 @@ layout_type (tree type)
TYPE_SIZE (type) = int_const_binop (MULT_EXPR, TYPE_SIZE (innertype),
bitsize_int (nunits));
- /* Always naturally align vectors. This prevents ABI changes
- depending on whether or not native vector modes are supported. */
- TYPE_ALIGN (type) = tree_low_cst (TYPE_SIZE (type), 0);
+ /* Naturally align vectors, but let the target set an upper
+ limit. This prevents ABI changes depending on whether or
+ not native vector modes are supported. */
+ TYPE_ALIGN (type)
+ = targetm.vector_alignment (type, tree_low_cst (TYPE_SIZE (type), 0));
break;
}
