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Re: PPC64 Compiler bug !!
- From: linas at austin dot ibm dot com
- To: Mike Stump <mrs at apple dot com>
- Cc: David Edelsohn <dje at watson dot ibm dot com>, Alan Modra <amodra at bigpond dot net dot au>, Steve Munroe <sjmunroe at us dot ibm dot com>, linuxppc64-dev at lists dot linuxppc dot org, alanm at redhat dot com, olh at suse dot com, peter at bergner dot org, gcc at gcc dot gnu dot org
- Date: Tue, 17 Jun 2003 11:28:49 -0500
- Subject: Re: PPC64 Compiler bug !!
- References: <20030613122344.A24578@forte.austin.ibm.com> <4C63A56E-A081-11D7-8138-003065A77310@apple.com>
On Mon, Jun 16, 2003 at 10:05:22PM -0700, Mike Stump wrote:
> On Friday, June 13, 2003, at 10:23 AM, linas@austin.ibm.com wrote:
> > Based on the email replies, and on a few tests run over here,
> > -msoft-float also seems to have the undocumented but valuable side
> > effect of preventing the use of FPR's in DImode moves.
>
> On processors that have specialized registers for the floating point
> unit, -msoft-float disappears those registers. This should be
> documented and certainly can be relied upon.
Well, that belies the point. I think I can safely state that most
programmers, when faced with an all-integer program, would assume
that the compiler generated pure-integer code, and thus it would
never occur to them to study or take interest in any float-point
flags.
That's what most of this sqwak is about.
> If you want to fix the documentation to be clearer, that'd be good.
I don't have commit access to the documentation source. Maybe
something along the following lines would be acceptable?
-msoft-float
-mhard-float
Generate code that does not use (uses) the floating-
point register set. Software floating point emulation
is provided if you use the -msoft-float option, and
pass the option to GCC when linking.
In some cases, gcc will use floating point registers
to temporarily hold 64-bit integer values. Specifying
-msoft-float will prevent this optimization from being
made.
> > My documentation seems to only mention -msoft-float for the DEC Alpha,
> > and not as a PPC flag.
>
> Odd. My documentation seems to have it:
Right. Very odd, it seem that man-db 2.4.1 is broken, cause I can
clearly see the docos in man 2.3.19. The gcc man page is OK, but
the latest man command can't find the string in the man page.
Ahh, bugs ...
--linas