[LLVMdev] Documentation of fmuladd intrinsic

[Hal Finkel]

----- Original Message -----
> From: dag at cray.com
> To: "Justin Holewinski" <justin.holewinski at gmail.com>
> Cc: "Hal Finkel" <hfinkel at anl.gov>, "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
> Sent: Friday, January 11, 2013 2:13:50 PM
> Subject: Re: [LLVMdev] Documentation of fmuladd intrinsic
> 
> Justin Holewinski <justin.holewinski at gmail.com> writes:
> 
> > Out of curiosity, what is the use-case for
> > isFMAFasterThanMulAndAdd?
> >  If a target declares that FMA is actually slower for a given type,
> > why not just declare it as illegal for that type?  Wouldn't that
> > accomplish the same thing without another target hook?  I feel like
> > I'm
> > missing something here.
> 
> It's not expressed in the code Hal posted but I suppose a target
> could
> have a slow fma that the user nonetheless wants to use for precision
> reasons.

Yes, I believe that's right. This way you can still always get an fma with the intrinsic.

 -Hal

> 
>                               -David
> 

-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory