[Mesa-dev] [PATCH] Add an accelerated version of F_TO_I for x86_64

[Jason Ekstrand]

On Mon, Jul 21, 2014 at 5:29 PM, Matt Turner <mattst88 at gmail.com> wrote:

> On Mon, Jul 21, 2014 at 5:16 PM, Jason Ekstrand <jason at jlekstrand.net>
> wrote:
> > Signed-off-by: Jason Ekstrand <jason.ekstrand at intel.com>
> > ---
> >  src/mesa/main/imports.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/src/mesa/main/imports.h b/src/mesa/main/imports.h
> > index af780b2..5d6486b 100644
> > --- a/src/mesa/main/imports.h
> > +++ b/src/mesa/main/imports.h
> > @@ -285,6 +285,10 @@ static inline int F_TO_I(float f)
> >     int r;
> >     __asm__ ("fistpl %0" : "=m" (r) : "t" (f) : "st");
> >     return r;
> > +#elif defined(USE_X86_64_ASM) && defined(__GNUC__)
> > +   int r;
> > +   __asm__ ("cvtss2si %1, %0" : "=r" (r) : "xm" (f));
>
> "xm"? I think you just want "x"
>

No, this is needed because it uses an SSE register.


>
> Also "=&r" since it's written without ever being read.
>

Reading the GCC docs, I don't see how earlyclobber is appropreate.  Would
you care to explain your reasoning further?


>
> > +   return r;
> >  #elif defined(USE_X86_ASM) && defined(_MSC_VER)
> >     int r;
> >     _asm {
> > --
>
> Remove the ' XXX We could use an x86-64/SSE2 version here.' comment
> above the function too.
>

Good catch


>
> I'd expect some data about this change. Performance data would be
> nice, but I'd take just the output of `size` on i965_dri.so.
>

Sure, I've got a little performance data if you'd like.
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