Patchwork [13/13] Use GCC builtins for copysign functions if desired.

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Submitter Stefan Liebler
Date Dec. 4, 2019, 1:15 p.m.
Message ID <e24d1f79-2402-d7cd-f80a-50be7ebad2b8@linux.ibm.com>
Download mbox | patch
Permalink /patch/36501/
State Superseded
Headers show

Comments

Stefan Liebler - Dec. 4, 2019, 1:15 p.m.
On 12/3/19 5:50 PM, Joseph Myers wrote:
> On Tue, 3 Dec 2019, Stefan Liebler wrote:
> 
>> On 12/2/19 10:00 PM, Joseph Myers wrote:
>>> On Mon, 2 Dec 2019, Stefan Liebler wrote:
>>>
>>>> This patch is using the corresponding GCC builtin for copysignf, copysign,
>>>> copysignl and copysignf128 if the USE_FUNCTION_BUILTIN macros are defined
>>>> to one
>>>> in math-use-builtins.h.
>>>
>>> I believe this is always safe for these implementations (the only case
>>> where GCC might not expand copysign functions inline is copysignl for IBM
>>> long double, in the soft-float case).
>>>
>> Thus you mean we can do the following preset in
>> sysdeps/generic/math-use-builtins.h?
>> #define USE_COPYSIGN_BUILTIN 1
>> #define USE_COPYSIGNF_BUILTIN 1
>> #define USE_COPYSIGNL_BUILTIN 0
>> #define USE_COPYSIGNF128_BUILTIN 0
>>
>> Or even also set USE_COPYSIGNL_BUILTIN to one as IBM long double has its own
>> implementation in ./sysdeps/ieee754/ldbl-128ibm/s_copysignl.c.
> 
> I think they can all be 1, given that IBM long double has its own
> implementation.  Except that you shouldn't need the indirection through
> these macros at all.  Just use __builtin_copysign etc. directly in the
> implementations (other than IBM long double), unconditionally, the same
> way that sysdeps/ieee754/dbl-64/s_fabs.c uses __builtin_fabs directly
> without such macros being needed.
> 

Okay. I've set them to 1 and also used build-many-glibcs.py and had a 
look into the s_copysign*.os files. There is no function call to 
copysign* itself.

If one architecture encounters issues with those builtins, an 
architecture specific math-use-builtins.sh file can set the macros to zero.

Bye,
Stefan
Joseph Myers - Dec. 4, 2019, 1:20 p.m.
On Wed, 4 Dec 2019, Stefan Liebler wrote:

> > I think they can all be 1, given that IBM long double has its own
> > implementation.  Except that you shouldn't need the indirection through
> > these macros at all.  Just use __builtin_copysign etc. directly in the
> > implementations (other than IBM long double), unconditionally, the same
> > way that sysdeps/ieee754/dbl-64/s_fabs.c uses __builtin_fabs directly
> > without such macros being needed.
> > 
> 
> Okay. I've set them to 1 and also used build-many-glibcs.py and had a look
> into the s_copysign*.os files. There is no function call to copysign* itself.

I think we should handle this like fabs and not have the macros at all, 
just call __builtin_copysign etc. unconditionally.

Patch

commit 91e337064c1684bd10c63ecc559e8340656f0cf5
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Mon Dec 2 15:32:44 2019 +0100

    Use GCC builtins for copysign functions if desired.
    
    This patch is using the corresponding GCC builtin for copysignf, copysign,
    copysignl and copysignf128 if the USE_FUNCTION_BUILTIN macros are defined to one
    in math-use-builtins.h.
    
    By default the float, double and long double macros are set to one.
    According to Joseph Myers it is safe to just use those builtins.
    Also the objdumps of s_copysign*.os files generated by build-many-glibcs.py
    do not show copysign* function calls.
    
    If one architecture encounters issues with those builtins, an architecture
    specific math-use-builtins.sh file can set the macros to zero.

diff --git a/sysdeps/generic/math-use-builtins.h b/sysdeps/generic/math-use-builtins.h
index 34ca438a8c..df8fc97a2e 100644
--- a/sysdeps/generic/math-use-builtins.h
+++ b/sysdeps/generic/math-use-builtins.h
@@ -51,4 +51,9 @@ 
 #define USE_ROUNDL_BUILTIN 0
 #define USE_ROUNDF128_BUILTIN 0
 
+#define USE_COPYSIGN_BUILTIN 1
+#define USE_COPYSIGNF_BUILTIN 1
+#define USE_COPYSIGNL_BUILTIN 1
+#define USE_COPYSIGNF128_BUILTIN 0
+
 #endif /* math-use-builtins.h */
diff --git a/sysdeps/ieee754/dbl-64/s_copysign.c b/sysdeps/ieee754/dbl-64/s_copysign.c
index 589b088c95..0be1a6420f 100644
--- a/sysdeps/ieee754/dbl-64/s_copysign.c
+++ b/sysdeps/ieee754/dbl-64/s_copysign.c
@@ -10,7 +10,9 @@ 
  * ====================================================
  */
 
-#if defined(LIBM_SCCS) && !defined(lint)
+#include <math-use-builtins.h>
+
+#if ! USE_COPYSIGN_BUILTIN && defined (LIBM_SCCS) && ! defined (lint)
 static char rcsid[] = "$NetBSD: s_copysign.c,v 1.8 1995/05/10 20:46:57 jtc Exp $";
 #endif
 
@@ -28,10 +30,14 @@  static char rcsid[] = "$NetBSD: s_copysign.c,v 1.8 1995/05/10 20:46:57 jtc Exp $
 double
 __copysign (double x, double y)
 {
+#if USE_COPYSIGN_BUILTIN
+  return __builtin_copysign (x, y);
+#else
   uint32_t hx, hy;
   GET_HIGH_WORD (hx, x);
   GET_HIGH_WORD (hy, y);
   SET_HIGH_WORD (x, (hx & 0x7fffffff) | (hy & 0x80000000));
   return x;
+#endif
 }
 libm_alias_double (__copysign, copysign)
diff --git a/sysdeps/ieee754/float128/float128_private.h b/sysdeps/ieee754/float128/float128_private.h
index a6c76ce364..7f7f904152 100644
--- a/sysdeps/ieee754/float128/float128_private.h
+++ b/sysdeps/ieee754/float128/float128_private.h
@@ -152,6 +152,8 @@ 
 #define USE_TRUNCL_BUILTIN USE_TRUNCF128_BUILTIN
 #undef USE_ROUNDL_BUILTIN
 #define USE_ROUNDL_BUILTIN USE_ROUNDF128_BUILTIN
+#undef USE_COPYSIGNL_BUILTIN
+#define USE_COPYSIGNL_BUILTIN USE_COPYSIGNF128_BUILTIN
 
 /* IEEE function renames.  */
 #define __ieee754_acoshl __ieee754_acoshf128
@@ -361,6 +363,7 @@ 
 #define __builtin_ceill __builtin_ceilf128
 #define __builtin_truncl __builtin_truncf128
 #define __builtin_roundl __builtin_roundf128
+#define __builtin_copysignl __builtin_copysignf128
 
 /* Get the constant suffix from bits/floatn-compat.h.  */
 #define L(x) __f128 (x)
diff --git a/sysdeps/ieee754/flt-32/s_copysignf.c b/sysdeps/ieee754/flt-32/s_copysignf.c
index 77d1d90e92..9a9e6389cd 100644
--- a/sysdeps/ieee754/flt-32/s_copysignf.c
+++ b/sysdeps/ieee754/flt-32/s_copysignf.c
@@ -13,7 +13,9 @@ 
  * ====================================================
  */
 
-#if defined(LIBM_SCCS) && !defined(lint)
+#include <math-use-builtins.h>
+
+#if ! USE_COPYSIGNF_BUILTIN && defined (LIBM_SCCS) && ! defined (lint)
 static char rcsid[] = "$NetBSD: s_copysignf.c,v 1.4 1995/05/10 20:46:59 jtc Exp $";
 #endif
 
@@ -28,12 +30,17 @@  static char rcsid[] = "$NetBSD: s_copysignf.c,v 1.4 1995/05/10 20:46:59 jtc Exp
 #include <math_private.h>
 #include <libm-alias-float.h>
 
-float __copysignf(float x, float y)
+float
+__copysignf (float x, float y)
 {
-	uint32_t ix,iy;
-	GET_FLOAT_WORD(ix,x);
-	GET_FLOAT_WORD(iy,y);
-	SET_FLOAT_WORD(x,(ix&0x7fffffff)|(iy&0x80000000));
-        return x;
+#if USE_COPYSIGNF_BUILTIN
+  return __builtin_copysignf (x, y);
+#else
+  uint32_t ix, iy;
+  GET_FLOAT_WORD (ix, x);
+  GET_FLOAT_WORD (iy, y);
+  SET_FLOAT_WORD (x, (ix & 0x7fffffff) | (iy & 0x80000000));
+  return x;
+#endif
 }
 libm_alias_float (__copysign, copysign)
diff --git a/sysdeps/ieee754/ldbl-128/s_copysignl.c b/sysdeps/ieee754/ldbl-128/s_copysignl.c
index a501139f71..6095b7fc73 100644
--- a/sysdeps/ieee754/ldbl-128/s_copysignl.c
+++ b/sysdeps/ieee754/ldbl-128/s_copysignl.c
@@ -13,7 +13,9 @@ 
  * ====================================================
  */
 
-#if defined(LIBM_SCCS) && !defined(lint)
+#include <math-use-builtins.h>
+
+#if ! USE_COPYSIGNL_BUILTIN && defined (LIBM_SCCS) && ! defined (lint)
 static char rcsid[] = "$NetBSD: $";
 #endif
 
@@ -28,13 +30,18 @@  static char rcsid[] = "$NetBSD: $";
 #include <math_private.h>
 #include <libm-alias-ldouble.h>
 
-_Float128 __copysignl(_Float128 x, _Float128 y)
+_Float128
+__copysignl (_Float128 x, _Float128 y)
 {
-	uint64_t hx,hy;
-	GET_LDOUBLE_MSW64(hx,x);
-	GET_LDOUBLE_MSW64(hy,y);
-	SET_LDOUBLE_MSW64(x,(hx&0x7fffffffffffffffULL)
-			    |(hy&0x8000000000000000ULL));
-        return x;
+#if USE_COPYSIGNL_BUILTIN
+  return __builtin_copysignl (x, y);
+#else
+  uint64_t hx, hy;
+  GET_LDOUBLE_MSW64 (hx, x);
+  GET_LDOUBLE_MSW64 (hy, y);
+  SET_LDOUBLE_MSW64 (x, (hx & 0x7fffffffffffffffULL)
+		     | (hy & 0x8000000000000000ULL));
+  return x;
+#endif
 }
 libm_alias_ldouble (__copysign, copysign)
diff --git a/sysdeps/s390/fpu/math-use-builtins.h b/sysdeps/s390/fpu/math-use-builtins.h
index 5838a31c50..ed2a05775f 100644
--- a/sysdeps/s390/fpu/math-use-builtins.h
+++ b/sysdeps/s390/fpu/math-use-builtins.h
@@ -50,6 +50,13 @@ 
 # define USE_ROUNDF_BUILTIN 1
 # define USE_ROUNDL_BUILTIN 1
 
+/* GCC emits the z9-ec zarch "copy sign" instruction for these
+   builtins if build with at least --march=z196 -mzarch.
+   Note: z196 is no typo but a bug in GCC!  */
+# define USE_COPYSIGN_BUILTIN 1
+# define USE_COPYSIGNF_BUILTIN 1
+# define USE_COPYSIGNL_BUILTIN 1
+
 # if __GNUC_PREREQ (8, 1)
 #  define USE_NEARBYINTF128_BUILTIN 1
 #  define USE_RINTF128_BUILTIN 1
@@ -57,6 +64,7 @@ 
 #  define USE_CEILF128_BUILTIN 1
 #  define USE_TRUNCF128_BUILTIN 1
 #  define USE_ROUNDF128_BUILTIN 1
+#  define USE_COPYSIGNF128_BUILTIN 1
 # else
 #  define USE_NEARBYINTF128_BUILTIN 0
 #  define USE_RINTF128_BUILTIN 0
@@ -64,6 +72,7 @@ 
 #  define USE_CEILF128_BUILTIN 0
 #  define USE_TRUNCF128_BUILTIN 0
 #  define USE_ROUNDF128_BUILTIN 0
+#  define USE_COPYSIGNF128_BUILTIN 0
 # endif
 
 #else