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

On 10/07/2015 11:22 AM, Joseph Myers wrote:
On Wed, 7 Oct 2015, Jeff Law wrote:

I'm not sure why this attribute isn't documented, but clearly that should be

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.
Seems reasonable.  I had a suspicion it was something of this nature.

I thought the ABI for this stuff was consistent across the implementations
(that was certainly the goal).  So aside from an example of how to use the
attribute to get calls into the vector math library, I'm not sure what's
needed.  Essentially the attribute is just another way to ensure we exploit
the vector library when possible.

Well, the ABI should at least say that the attribute has the same
implications as the pragma regarding what vector function versions are
available.  (So that a future compiler building with -mavx1024 won't
interpret old glibc headers as meaning that AVX1024 function versions are
available in old glibc - that will instead require a further attribute /
pragma to declare availability of those versions.)
Also seems reasonable. Thanks for clarifying the longer term implications you're concerned about.


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