Patchwork [powerpc] fegetround: utilize faster method to get rounding mode

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Submitter Paul Clarke
Date June 6, 2019, 7:22 p.m.
Message ID <1559848943-9717-1-git-send-email-pc@us.ibm.com>
Download mbox | patch
Permalink /patch/33042/
State New
Headers show

Comments

Paul Clarke - June 6, 2019, 7:22 p.m.
From: "Paul A. Clarke" <pc@us.ibm.com>

Add support to use 'mffsl' instruction if compiled for POWER9 (or later).

2019-06-06  Paul A. Clarke  <pc@us.ibm.com>

	* sysdeps/powerpc/bits/fenvinline.h (__fegetround): Add new
	implementation for _ARCH_PWR9.
---
 sysdeps/powerpc/bits/fenvinline.h | 9 +++++++++
 1 file changed, 9 insertions(+)
Tulio Magno Quites Machado Filho - June 11, 2019, 6:42 p.m.
"Paul A. Clarke" <pc@us.ibm.com> writes:

> From: "Paul A. Clarke" <pc@us.ibm.com>
>
> Add support to use 'mffsl' instruction if compiled for POWER9 (or later).
>
> 2019-06-06  Paul A. Clarke  <pc@us.ibm.com>
>
> 	* sysdeps/powerpc/bits/fenvinline.h (__fegetround): Add new
> 	implementation for _ARCH_PWR9.

I think you can use this ChangeLog format instead:

	* sysdeps/powerpc/bits/fenvinline.h [_ARCH_PWR9] (__fegetround): ...

> diff --git a/sysdeps/powerpc/bits/fenvinline.h b/sysdeps/powerpc/bits/fenvinline.h
> index 7079d1a..ba23da1 100644
> --- a/sysdeps/powerpc/bits/fenvinline.h
> +++ b/sysdeps/powerpc/bits/fenvinline.h
> @@ -19,12 +19,21 @@
>  #if defined __GNUC__ && !defined _SOFT_FLOAT && !defined __NO_FPRS__
>  
>  /* Inline definition for fegetround.  */
> +#ifdef _ARCH_PWR9
> +# define __fegetround()							\
> +  __extension__  ({							\
> +    union { double __d; unsigned long long __ll; } __u;			\
> +    __asm__ ("mffsl %0" : "=f" (__u.__d));				\
> +    __u.__ll & 0x0000000000000003LL;					\
> +  })
> +#else
>  # define __fegetround() \
>    (__extension__  ({ int __fegetround_result;				      \
>  		     __asm__ __volatile__				      \
>  		       ("mcrfs 7,7 ; mfcr %0"				      \
>  			: "=r"(__fegetround_result) : : "cr7");		      \
>  		     __fegetround_result & 3; }))
> +#endif

After applying this patch, I started seeing failures on math/test-fenv-tls
when using GCC 9.1 on POWER9.
I'm configuring with --with-cpu=power9

I can't reproduce it with GCC 8.3.

There are only 2 mffsl in test_round().  This is suspicious.

Patch

diff --git a/sysdeps/powerpc/bits/fenvinline.h b/sysdeps/powerpc/bits/fenvinline.h
index 7079d1a..ba23da1 100644
--- a/sysdeps/powerpc/bits/fenvinline.h
+++ b/sysdeps/powerpc/bits/fenvinline.h
@@ -19,12 +19,21 @@ 
 #if defined __GNUC__ && !defined _SOFT_FLOAT && !defined __NO_FPRS__
 
 /* Inline definition for fegetround.  */
+#ifdef _ARCH_PWR9
+# define __fegetround()							\
+  __extension__  ({							\
+    union { double __d; unsigned long long __ll; } __u;			\
+    __asm__ ("mffsl %0" : "=f" (__u.__d));				\
+    __u.__ll & 0x0000000000000003LL;					\
+  })
+#else
 # define __fegetround() \
   (__extension__  ({ int __fegetround_result;				      \
 		     __asm__ __volatile__				      \
 		       ("mcrfs 7,7 ; mfcr %0"				      \
 			: "=r"(__fegetround_result) : : "cr7");		      \
 		     __fegetround_result & 3; }))
+#endif
 # define fegetround() __fegetround ()
 
 # ifndef __NO_MATH_INLINES