[RFC, VECTOR ABI] Allow __attribute__((vector)) in GCC by default.

[Jeff Law]

On 10/07/2015 11:34 AM, Ramana Radhakrishnan wrote:
> On Wed, Oct 7, 2015 at 6:22 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>> On Wed, 7 Oct 2015, Jeff Law wrote:
>>
>>> I'm not sure why this attribute isn't documented, but clearly that should be
>>> fixed.
>>
>> I assume the reasoning was: we document support for Cilk+ (and what's
>> included in Cilk+ is externally documented).  When it becomes a generic
>> GNU C attribute, that reasoning no longer applies.
>
>
> I do not understand enough of this feature but since this is becoming
> a GNU C attribute, what happens with functions which are marked
> __attribute__((vector)) but are compiled for platforms that do not
> support vector clones or have options to compile for soft float - what
> is the expected behaviour for the compiler in those situations ?
> Presumably the __attribute__((vector)) has no effect ? Might also be
> useful to document that.
ISTM it should be a nop in those cases and yes, documenting and testing 
those cases seems wise.  Anything else is just asking for trouble.  So 
Kirill, some simple tests for those cases seems advisable.

ISTM that in an ideal world, for all targets with vector hardware that 
we ought to work towards getting clone support and vector entry points 
in the math library.  Not sure where that'll land on everyone's priority 
list though.

jeff