Re: [RFC PATCH] softfloat: use QEMU_FLATTEN to avoid mistaken isra inlining

[BALATON Zoltan]

On Thu, 25 May 2023, Paolo Bonzini wrote:
> On 5/23/23 16:33, Richard Henderson wrote:
> > The tests are poorly ordered, testing many unlikely things before the most 
> > likely thing (normal).  A better ordering would be
> >
> >      if (likely(tp##_is_normal(arg))) {
> >      } else if (tp##_is_zero(arg)) {
> >      } else if (tp##_is_zero_or_denormal(arg)) {
> >      } else if (tp##_is_infinity(arg)) {
> >      } else {
> >          // nan case
> >      }
>
> Might also benefit from a is_finite (true if zero or normal or denormal) 
> predicate, to do
>
> if (tp##_is_finite(arg)) {

There seems to be only is_infinity but I'm not sure if is_finite would be 
the same as !is_infinity so could not try this. But it seems having any 
branches kills performance so adding more branches may not help (also 
because infinite values may be less frequent so not sure why this would 
be better).

Regards,
BALATON Zoltan

>    if (!tp##_is_zero_or_denormal(arg)) {
>       // normal
>    } else if (tp##_is_zero(arg)) {
>    } else {
>       // denormal
>    }
> } else if (tp##_is_infinity(arg)) {
> } else {
>    // nan
> }
>
> since is_normal is a bit more complex and inefficient than the others. The 
> compiler should easily reuse the result of masking away the sign bit.
>
> Paolo