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

Sandeep Patel deeppatel1987 at gmail.com
Tue Jun 19 11:56:13 PDT 2012


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.

deep



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