[PATCH v3 1/6] rs6000: Support SSE4.1 "round" intrinsics

[Segher Boessenkool]

On Mon, Aug 23, 2021 at 02:03:05PM -0500, Paul A. Clarke wrote:
> No attempt is made to optimize writing the FPSCR (by checking if the new
> value would be the same), other than using lighter weight instructions
> when possible.

__builtin_set_fpscr_rn makes optimised code (using mtfsb[01])
automatically, fwiw.

> Move implementations of _mm_ceil* and _mm_floor* into _mm_round*, and
> convert _mm_ceil* and _mm_floor* into macros. This matches the current
> analogous implementations in config/i386/smmintrin.h.

Hrm.  Using function-like macros is begging for trouble, as usual.  But
the x86 version does this, so meh.

> +extern __inline __m128d
> +__attribute__ ((__gnu_inline__, __always_inline__, __artificial__))
> +_mm_round_pd (__m128d __A, int __rounding)
> +{
> +  __v2df __r;
> +  union {
> +    double __fr;
> +    long long __fpscr;
> +  } __enables_save, __fpscr_save;
> +
> +  if (__rounding & _MM_FROUND_NO_EXC)
> +    {
> +      /* Save enabled exceptions, disable all exceptions,
> +	 and preserve the rounding mode.  */
> +#ifdef _ARCH_PWR9
> +      __asm__ __volatile__ ("mffsce %0" : "=f" (__fpscr_save.__fr));

The __volatile__ does likely not do what you want.  As far as I can see
you do not want one here anyway?

"volatile" does not order asm wrt fp insns, which you likely *do* want.

> +  __v2df __r = { ((__v2df)__B)[0], ((__v2df) __A)[1] };

You put spaces after only some casts, btw?  Well maybe I found the one
place you did it wrong, heh :-)  And you can avoid having so many parens
by making extra variables -- much more readable.

> +  switch (__rounding)

You do not need any of that __ either.

> +/* { dg-do run } */
> +/* { dg-require-effective-target powerpc_vsx_ok } */
> +/* { dg-options "-O2 -mvsx" } */

"dg-do run" requires vsx_hw, not just vsx_ok.  Testing on a machine
without VSX (so before p7) would have shown that, but do you have access
to any?  This is one of those things we are only told about a year after
it was added, because no one who tests often does that on so old
hardware :-)

So, okay for trunk (and backports after some burn-in) with that vsx_ok
fixed.  That asm needs fixing, but you can do that later.

Thanks!


Segher