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


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 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.)

-- 
Joseph S. Myers
joseph@codesourcery.com


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