Re: GCC floating point usage

[Mark Mitchell <mark at codesourcery dot com>]

--On Monday, October 14, 2002 09:59:00 AM -0700 Zack Weinberg 
<zack@codesourcery.com> wrote:

> On Mon, Oct 14, 2002 at 12:37:14PM -0400, David Edelsohn wrote:
> > >>>>> Stefan Bylund writes:
> >
> > Stefan> Is it possible to somehow instruct GCC to only generate
> > Stefan> floating point instructions for C/C++ float/double
> > Stefan> operations and not for internal non-floating point
> > Stefan> optimizations etc?
> >
> > 	If you do not want to use the FPU, then invoke the compiler with
> > the -msoft-float PowerPC option.  If the FPRs are present and it is
> > efficient to use them, the compiler will use them.
> Come now, what he wants is not unreasonable.  "If floating point
> operations appeared in the source code, generate hardware floating
> point instructions; otherwise, generate only integer-unit
> instructions."  I (that is, CodeSourcery) have a customer that needs
> precisely this; in fact I posted a patch to implement it for PPC last
> fall.  Now seems like a reasonable time to bring this issue back up.
I agree, on all points:

(1) Clearly, many people have a real need for this fuctionality.

(2) You are correct; if the user has told the compiler not to use
   hardware FP unless floating point operations appear in the code,
   then the MD should not pretend it knows how to do moves that it
   can only do with FP registers.

With the caveat that you perserve the current default behavior, the
patch is OK for the b-i-b, assuming that you do not hear objections
from the RS6000 maintainers within a couple of days.  If they do
object, we will figure out what to do.

--
Mark Mitchell                mark@codesourcery.com
CodeSourcery, LLC            http://www.codesourcery.com