Subject: Re: I want to rid ugly float load/stores used only for data movement
To: Jason R Thorpe <>
From: None <>
List: tech-toolchain
Date: 03/03/2003 00:27:17
> On Sat, Feb 22, 2003 at 06:09:13PM -0500, David Edelsohn wrote:
>  > MLR> Would anyone point me in the correct direction?
>  > 
>  > 	Your intent cannot be implemented safely in GCC.  If GCC knows it
>  > has FPRs and FPRs hold 64-bit values (which they must), it will use them
>  > for 64-bit moves.  Cannot be avoided safely.
> That's kind of a bummer.  I seem to recall the idea of "no-implicit-fp"
> coming up on the GCC mailing list recently, too.  The reason people want
> is to eliminate unpredictable context switch times and/or speed up context
> switching.

Yes. Check GCC's CVS and I think you will find that this is fixed.

This "implicit FP" stuff was causing trouble on VxWorks; Wind River raised
this issue with the FSF.

As I recall, the decision was to abandon this sly use of FP registers.
So, at some point, bringing in a new GCC should fix it.

BTW, Mouse: GCC already avoids this tactic on chips for which FP registers
do not hold arbitrary values (i386, m68k, to name a couple). Please, give
them _some_ credit.

Todd Whitesel
toddpw @