Re: [ASM] [PowerPC] floating-point registers mnemonics

[Andrew Haley <aph at redhat dot com>]

On 01/14/2011 05:13 PM, Segher Boessenkool wrote:
> > On the code below, I'm storing the result of the product in a temporary
> > variable (fra).
> >
> > inline void MTH_Vec3Scale(register MTH_tt_Vector3 *D,register const
> > MTH_tt_Vector3 *A, register f32 f)
> > {
> >      register       f32  fra;
> >      asm     (       "lfs   %3,   0(%0)              \n"        // FRA<-
> > *A
> >                      "\t    fmul   %3,   %3,     %2  \n"       // FRT<-
> > FRA
> > * FRC
> >                      "\t    stfs   %3,   0(%1)       \n"         // *dest =
> > FRT
> >
> >                      "\t    lfs    %3,   4(%0)       \n"
> >                      "\t    fmul   %3,   %3,     %2  \n"
> >                      "\t    stfs   %3,   4(%1)       \n"
> >
> >                      "\t    lfs    %3,   8(%0)       \n"
> >                      "\t    fmul   %3,   %3,     %2  \n"
> >                      "\t    stfs   %3,   8(%1)       \n"
> >          /* outputs: */ :
> >          /* inputs : */ :"b"(A),"b"(D),"f"(f),"f"(fra)
> >          /* clobbers:*/ :"memory");
> > }
>
> You write to "fra" (and never read it), so you should list it in
> outputs instead of in inputs:
>
>           /* outputs: */ :"=f"(fra)

Make that an earlyclobber: "=&f"

Andrew.