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

From: Stefan Liebler <stli at linux dot ibm dot com>
To: libc-alpha at sourceware dot org
Cc: Stefan Liebler <stli at linux dot ibm dot com>
Date: Mon, 2 Dec 2019 15:46:17 +0100
Subject: [PATCH 13/13] Use GCC builtins for copysign functions if desired.
References: <1575297977-2589-1-git-send-email-stli@linux.ibm.com>

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.

This is the case for s390 if build with at least --march=z196 --mzarch.
Otherwise the generic implementation is used.
Note: z196 is no typo but a bug in GCC!
---
 sysdeps/generic/math-use-builtins.h         |  5 +++++
 sysdeps/ieee754/dbl-64/s_copysign.c         |  8 ++++++-
 sysdeps/ieee754/float128/float128_private.h |  3 +++
 sysdeps/ieee754/flt-32/s_copysignf.c        | 21 ++++++++++++-------
 sysdeps/ieee754/ldbl-128/s_copysignl.c      | 23 ++++++++++++++-------
 sysdeps/s390/fpu/math-use-builtins.h        |  9 ++++++++
 6 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/sysdeps/generic/math-use-builtins.h b/sysdeps/generic/math-use-builtins.h
index 34ca438a8c..a22d787791 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 0
+#define USE_COPYSIGNF_BUILTIN 0
+#define USE_COPYSIGNL_BUILTIN 0
+#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
-- 
2.19.1

Follow-Ups:
- Re: [PATCH 13/13] Use GCC builtins for copysign functions if desired.
  - From: Joseph Myers

References:
- [PATCH 00/13] Use GCC builtins for some math functions if desired.
  - From: Stefan Liebler

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