[EXTERNAL] Re: [Patch 1/5] rs6000, Add 128-bit sign extension support

will schmidt will_schmidt@vnet.ibm.com
Thu Aug 13 22:11:11 GMT 2020


On Thu, 2020-08-13 at 13:29 -0500, Segher Boessenkool wrote:
> On Thu, Aug 13, 2020 at 11:09:10AM -0700, Carl Love wrote:
> > The builtins
> > 
> > vector signed int vec_signexti (vector signed char a)
> > vector signed long long vec_signextll (vector signed char a)
> > vector signed int vec_signexti (vector signed short a)
> > vector signed long long vec_signextll (vector signed short a)
> > vector signed long long vec_signextll (vector signed int a)
> > 
> > were defined in the function prototypes directory in box called
> > "RFC
> > 2608 - 128-bit Binary Integer Operations".  The document the new
> > P10
> > builtins.  However, this subset of the newly defined builtins for
> > P10
> > can be implemented with existing Power 9 instructions.  That was
> > the
> > point of the comment.
> 
> Ah, I see :-)
> 
> > That is probably a level of detail that is not
> > really needed in the GCC code comment.  Probably best to just
> > change
> > the comment to read something like "ISA 3.0 sign extend builtins". 
> 
> Sounds good.

As long as there are no issues defining the builtins for 3.0 here.
AFAIK they are not documented in ISA 3.0.  This is a happy accident
that these ISA 3.1 builtins can be implemented with existing support.

> 
> > My thought for calling it out is that they could be back ported to
> > an
> > earlier GCC version since they use Power 9 instructions but it is
> > probably not worth the effort unless there is an explicit request
> > for
> > them. 
> 
> Yeah.  Thanks for the explanation!
> 
> 
> Segher



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