PPC64 Compiler bug !!

linas@austin.ibm.com linas@austin.ibm.com
Tue Jun 17 17:51:00 GMT 2003

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

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?

           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 

> > 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 ... 


More information about the Gcc mailing list