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Re: ppc64 floating point usage [was Re: PPC64 Compiler bug !!]


On Sat, Jun 14, 2003 at 08:59:25AM -0500, Michael S. Zick wrote:
> On Friday 13 June 2003 05:38 pm, Michael Meissner wrote:
> > On Fri, Jun 13, 2003 at 04:07:45PM -0500, Michael S. Zick wrote:
> > > On Friday 13 June 2003 04:02 pm, linas@austin.ibm.com wrote:
> > > > On Fri, Jun 13, 2003 at 04:09:06PM -0400, David Edelsohn wrote:
> > > >
> > > > Bird in hand vs. two in the bush.  We have Alan Modra's patch now, we
> > > > don't have an acceptable -mno-implicit-float patch.
> > > >
> > > > There is concern that Alan's patch will negatively impact performance
> > > > of fp code.  Is there a way to unambiguously resolve this issue, or
> > > > at least resolve it to everyones satisfaction?
> > >
> > > A patch for a related issue just appeared for gas-arm-Linux and
> > > gas-arm-NetBSD...
> > > <http://sources.redhat.com/ml/binutils/2003-06/msg00494.html>
> > > <http://sources.redhat.com/ml/binutils/2003-06/msg00497.html>
> > >
> > > Perhaps a similar route could be followed (I.E: -mfpu=none) to
> > > support developers that need the "never, ever, for any reason"
> > > touch the fp registers.
> >
> > Ummm, you already have that, it is spelled -msoft-float.  I don't
> > understand what a separate switch buys you.
> >
> My bad, I misunderstood the issue.
> I thought someone pointed out that -msoft-float did not eleminate
> all usage of float instructions (hardware OR software).

You might have been thinking about the alpha.  IIRC, the alpha's -msoft-float
doesn't eliminate all fp regs because the arch. manual says that fp regs must
be provided even if you don't have fp instructions.  However, for at least the
last 8 years or so, the rs6000/powerpc port -msoft-float option disables all FP
registers from being allocated.

-- 
Michael Meissner
email: gnu@the-meissners.org
http://www.the-meissners.org


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