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Re: [committed vms/ia64] Allow fused-madd operations
On Thu, 2010-10-21 at 11:09 +0200, Tristan Gingold wrote:
> On Oct 21, 2010, at 10:58 AM, Richard Guenther wrote:
>
> > On Thu, Oct 21, 2010 at 10:02 AM, Tristan Gingold <gingold@adacore.com> wrote:
> >> Hi,
> >>
> >> there are no reason not to allow fused madd by default on ia64/vms.
> >
> > Will that enable FP contraction for a*b+c by default?
>
> Yes.
>
> > That would be wrong code
> > unless you document the implementation defined initial state of FP_CONTRACT
> > to on on ia64/vms.
>
> Well, this patch just align ia64/vms with other ia64 platforms (linux, hpux) which have this flag set by default.
> So maybe we should simply document that all ia64 platform have FP_CONTRACT on by default ? (Steve CC:)
>
> (We did that so that floating point code behave the same between the ia64 platforms).
>
> Tristan.
I think the documentation for all the platforms that support FP
contractions (FUSED_MADD) is wrong. In doc/implement-c.tex it says:
Expressions are currently only contracted if
@option{-funsafe-math-optimizations} or @option{-ffast-math} are used.
This is subject to change.
All the platforms that support FUSED_MADD (ia64, mips, rs6000, i386,
s390, xtensa) seem to have it on by default, so maybe we should change
the documentation to say that.
Steve Ellcey
sje@cup.hp.com