[PATCH] S390: Allow "v" constraint for long double math_opt_barrier and math_force_eval with GCC 11.

[PATCH] S390: Allow "v" constraint for long double math_opt_barrier and math_force_eval with GCC 11.

[Stefan Liebler]

Starting with GCC 11, long double values can also be processed in vector
registers if build with -march >= z14.  Then GCC defines the
__LONG_DOUBLE_VX__ macro.

FYI: GCC commit "IBM Z: Introduce __LONG_DOUBLE_VX__ macro"
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=f47df2af313d2ce7f9149149010a142c2237beda
---
 sysdeps/s390/fpu/math-barriers.h | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/sysdeps/s390/fpu/math-barriers.h b/sysdeps/s390/fpu/math-barriers.h
index 68a3e55098..a47cda8b24 100644
--- a/sysdeps/s390/fpu/math-barriers.h
+++ b/sysdeps/s390/fpu/math-barriers.h
@@ -25,9 +25,22 @@
 # define ASM_CONSTRAINT_VR
 #endif
 
+/* Starting with gcc 11, long double values can also be processed in vector
+   registers if build with -march >= z14.  Then GCC defines the
+   __LONG_DOUBLE_VX__ macro.  */
+#ifdef __LONG_DOUBLE_VX__
+# define ASM_LONG_DOUBLE_IN_VR 1
+#else
+# define ASM_LONG_DOUBLE_IN_VR 0
+#endif
+
 #define math_opt_barrier(x)						\
   ({ __typeof (x) __x = (x);						\
-    if (__builtin_types_compatible_p (__typeof (x), _Float128))		\
+    if (! ASM_LONG_DOUBLE_IN_VR						\
+	&& (__builtin_types_compatible_p (__typeof (x), _Float128)	\
+	    || __builtin_types_compatible_p (__typeof (x), long double)	\
+	    )								\
+	)								\
       __asm__ ("# math_opt_barrier_f128 %0" : "+fm" (__x));		\
     else								\
       __asm__ ("# math_opt_barrier %0"					\
@@ -35,7 +48,11 @@
     __x; })
 #define math_force_eval(x)						\
   ({ __typeof (x) __x = (x);						\
-    if (__builtin_types_compatible_p (__typeof (x), _Float128))		\
+    if (! ASM_LONG_DOUBLE_IN_VR						\
+	&& (__builtin_types_compatible_p (__typeof (x), _Float128)	\
+	    || __builtin_types_compatible_p (__typeof (x), long double) \
+	    )								\
+	)								\
       __asm__ __volatile__ ("# math_force_eval_f128 %0"			\
 			    : : "fm" (__x));				\
     else								\
-- 
2.29.2

Re: [PATCH] S390: Allow "v" constraint for long double math_opt_barrier and math_force_eval with GCC 11.

[Florian Weimer]

* Stefan Liebler via Libc-alpha:

 with GCC 11, long double values can also be processed in vector
> registers if build with -march >= z14.  Then GCC defines the
> __LONG_DOUBLE_VX__ macro.
>
> FYI: GCC commit "IBM Z: Introduce __LONG_DOUBLE_VX__ macro"
> https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=f47df2af313d2ce7f9149149010a142c2237beda
> ---
>  sysdeps/s390/fpu/math-barriers.h | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/s390/fpu/math-barriers.h b/sysdeps/s390/fpu/math-barriers.h
> index 68a3e55098..a47cda8b24 100644
> --- a/sysdeps/s390/fpu/math-barriers.h
> +++ b/sysdeps/s390/fpu/math-barriers.h
> @@ -25,9 +25,22 @@
>  # define ASM_CONSTRAINT_VR
>  #endif
>  
> +/* Starting with gcc 11, long double values can also be processed in vector
> +   registers if build with -march >= z14.  Then GCC defines the
> +   __LONG_DOUBLE_VX__ macro.  */
> +#ifdef __LONG_DOUBLE_VX__
> +# define ASM_LONG_DOUBLE_IN_VR 1
> +#else
> +# define ASM_LONG_DOUBLE_IN_VR 0
> +#endif

Above that there is:

  #ifdef HAVE_S390_VX_GCC_SUPPORT
  # define ASM_CONSTRAINT_VR "v"
  #else
  # define ASM_CONSTRAINT_VR
  #endif

I think conceptually, ASM_LONG_DOUBLE_IN_VR should be set under
HAVE_S390_VX_GCC_SUPPORT, right?

Or maybe enforce this with #error?

Re: [PATCH] S390: Allow "v" constraint for long double math_opt_barrier and math_force_eval with GCC 11.

[Stefan Liebler]

On 31/03/2021 11:34, Florian Weimer wrote:
> * Stefan Liebler via Libc-alpha:
>> +/* Starting with gcc 11, long double values can also be processed in vector
>> +   registers if build with -march >= z14.  Then GCC defines the
>> +   __LONG_DOUBLE_VX__ macro.  */
>> +#ifdef __LONG_DOUBLE_VX__
>> +# define ASM_LONG_DOUBLE_IN_VR 1
>> +#else
>> +# define ASM_LONG_DOUBLE_IN_VR 0
>> +#endif
> 
> Above that there is:
> 
>   #ifdef HAVE_S390_VX_GCC_SUPPORT
>   # define ASM_CONSTRAINT_VR "v"
>   #else
>   # define ASM_CONSTRAINT_VR
>   #endif
> 
> I think conceptually, ASM_LONG_DOUBLE_IN_VR should be set under
> HAVE_S390_VX_GCC_SUPPORT, right?

Hi Florian,

yes, you are right. GCC will only define __LONG_DOUBLE_VX__ if it knows
about vector registers and HAVE_S390_VX_GCC_SUPPORT will always be
defined in this case.

If HAVE_S390_VX_GCC_SUPPORT would not be defined, but
__LONG_DOUBLE_VX__, then the constraint "fm" will be used in all asm
statements.

But nevertheless, setting ASM_LONG_DOUBLE_IN_VR under
HAVE_S390_VX_GCC_SUPPORT makes it more cleanly. I've just posted a v2:
https://sourceware.org/pipermail/libc-alpha/2021-March/124606.html

Thanks,
Stefan