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


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


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