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

[Segher Boessenkool]

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.

> 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