[llvm-commits] [PATCH] Aggressive FMA formation mode.

Hal Finkel hfinkel at anl.gov
Tue Jun 19 13:03:33 PDT 2012


On Tue, 19 Jun 2012 18:56:13 +0000
Sandeep Patel <deeppatel1987 at gmail.com> wrote:

> On Tue, Jun 19, 2012 at 4:58 AM, Hal Finkel <hfinkel at anl.gov> wrote:
> > On Mon, 18 Jun 2012 20:41:56 -0700
> > Lang Hames <lhames at gmail.com> wrote:
> >
> >> Hal - I've updated the guards on FMA formation for PPC, but by
> >> default FMAs will no longer be formed. If this is a problem, would
> >> it be possible to have your FMA-formation guard rely on a PPC
> >> specific "disable-FMA" option? I'd like to keep
> >> AllowExcessFPPrecision as the guard for target independent FMA
> >> formation, and that should be off by default.
> >
> > We can have it off by default. In the name of having a uniform
> > policy which defaults to IEEE compliance, that's fine, and I can
> > explain that to my users, etc. We should also document this
> > prominently on the clang web page (especially if this differs from
> > gcc's default behavior).
> 
> FWIW, this will lower amateur benchmark scoring runs. (e.g. Phoronix).
> 
> Strict IEEE conformance is far less likely to be desired than fast
> code. In my experience, the only users who want strict conformance are
> the authors of math libraries and the occasional application like ray
> tracing where denormals are common.

FWIW, as I've stated previously, I agree with this. The consensus on
this list (I think) has been in favor of strict conformance by
default. Given that, I favor consistency across all platforms. Having
strict conformance by default on some platforms and not on others, I
think, will be even more confusing than having a uniform rule.

 -Hal

> 
> deep



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



More information about the llvm-commits mailing list