Re: [PATCH] powerpc: fenvinline.h refactor

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 23/01/2020 15:14, Rogerio Alves wrote:
> Hi,
> 
> Attached to this email is a patch to refactor fenvinline.h for power to include some __buitins when available. I also removed a weird asm constraint. I can't reproduce the warning described on the file and the test passed. Not sure why the put that constraint. I will appreciate any reviews.

PS: please send the patch inline next time, it helps the review
process.

> 
> Regard

> From dbeca754bcbc6c77b6157a2f818554db31bac2ba Mon Sep 17 00:00:00 2001
> From: Rogerio Alves <rcardoso@linux.ibm.com>
> Date: Thu, 23 Jan 2020 14:54:00 -0300
> Subject: [PATCH v1] powerpc: Refactor fenvinline.h
> 
> This patch refactor fenviline.h replaces some statements for
> builtins.
> 
> 2020-01-22  Rogerio A. Cardoso  <rcardoso@linux.ibm.com>
> 
> 	* sysdeps/unix/sysv/linux/powerpc/bits/fenvline.h:
>     Replace expression by __builtin_popcount. Use
>     __builtin_mtfsb[01] when avaliable. Remove weird i#*X
>     asm constraint.

No ChangeLog entry required anymore.

> ---
>  sysdeps/powerpc/bits/fenvinline.h | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/sysdeps/powerpc/bits/fenvinline.h b/sysdeps/powerpc/bits/fenvinline.h
> index 70689664e2..ae04ece189 100644
> --- a/sysdeps/powerpc/bits/fenvinline.h
> +++ b/sysdeps/powerpc/bits/fenvinline.h
> @@ -15,7 +15,7 @@
>     You should have received a copy of the GNU Lesser General Public
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
> -
> +#include <stdio.h>

This is most likely not required.

>  #if defined __GNUC__ && !defined _SOFT_FLOAT && !defined __NO_FPRS__
>  
>  /* Inline definitions for fegetround.  */
> @@ -51,9 +51,16 @@
>  # define fegetround() __fegetround ()
>  
>  # ifndef __NO_MATH_INLINES
> -/* The weird 'i#*X' constraints on the following suppress a gcc
> -   warning when __excepts is not a constant.  Otherwise, they mean the
> -   same as just plain 'i'.  */

This is an installed header which can potentially be used with a older
gcc version. It is most likely an old bug fixed on newer release, so to
use the plain 'i' constrain you need to set it to use iff with a gcc
version where the warning surely does not happen. 

> +
> +/* Builtins to mtfsb0 and mtfsb1 was introduced on GCC 9.  */
> +#  if !__GNUC_PREREQ(9, 0)
> +
> +#   define __builtin_mtfsb0(__b)					\
> +   __asm__ __volatile__ ("mtfsb0 %0" : : "i" __b)
> +
> +#   define __builtin_mtfsb1(__b)					\
> +   __asm__ __volatile__ ("mtfsb1 %0" : : "i" __b)
> +#  endif

I don't think it is a good practice to re-define bultins, use it along with 
an extra indirection instead.  Something as:

  #  if !__GNUC_PREREQ(9, 0)
  #   define __mtfsb0(__b) __asm__ __volatile__ ("mtfsb0 %0" : : "i" (__b))
  #   define __mtfsb1(__b) __asm__ __volatile__ ("mtfsb1 %0" : : "i" (__b))
  #  else
  #   define __mtfsb0(__b) __builtin_mtfsb0 (__b)
  #   define __mtfsb1(__b) __builtin_mtfsb1 (__b)
  #  endif

>  
>  #  if __GNUC_PREREQ(3, 4)
>  
> @@ -63,12 +70,11 @@
>      int __e = __excepts;						      \
>      int __ret;								      \
>      if (__builtin_constant_p (__e)					      \
> -        && (__e & (__e - 1)) == 0					      \
> +        && (__builtin_popcount (__e) == 1)				      \

Why change this code? The idea is not emit any of the check for constant
call with only one FE_* flag (either mtfsb0 or mtfsb1).

>          && __e != FE_INVALID)						      \
>        {									      \
>  	if (__e != 0)							      \
> -	  __asm__ __volatile__ ("mtfsb1 %0"				      \
> -				: : "i#*X" (__builtin_clz (__e)));	      \
> +	  __builtin_mtfsb1 ((__builtin_clz (__e)));			      \
>          __ret = 0;							      \
>        }									      \
>      else								      \
> @@ -82,12 +88,11 @@
>      int __e = __excepts;						      \
>      int __ret;								      \
>      if (__builtin_constant_p (__e)					      \
> -        && (__e & (__e - 1)) == 0					      \
> +        && (__builtin_popcount (__e) == 1)				      \
>          && __e != FE_INVALID)						      \
>        {									      \
>  	if (__e != 0)							      \
> -	  __asm__ __volatile__ ("mtfsb0 %0"				      \
> -				: : "i#*X" (__builtin_clz (__e)));	      \
> +	  __builtin_mtfsb0 ((__builtin_clz (__e)));			      \
>          __ret = 0;							      \
>        }									      \
>      else								      \
> -- 
> 2.17.1