[PATCH] math: Enable some math builtins for clang

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

This patch enable the builtin usage for clang for the C99 functions
fpclassify, isfinite, isnormal, isnan, isinf, and sigbit.  This allows
clang optimize the calls on frontend instead of call the appropriate
glibc symbols.

Checked on aarch64-linux-gnu and x86_64-linux-gnu. I checked the supported
version for each builtin based on released version from clang/llvm.

	* math/math.h (fpclassify, isfinite, isnormal, isnan): Use builtin for
	clang 2.8.
	(signbit): Use builtin for clang 3.3.
	(isinf): Use builtin for clang 3.7.
---
 ChangeLog   |  7 +++++++
 math/math.h | 17 +++++++++++------
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/math/math.h b/math/math.h
index ffbc24af09..d70ec3877c 100644
--- a/math/math.h
+++ b/math/math.h
@@ -874,7 +874,8 @@ enum
    the __SUPPORT_SNAN__ check may be skipped for those versions.  */
 
 /* Return number of classification appropriate for X.  */
-# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__			      \
+# if ((__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__)		      \
+      || __glibc_clang_prereq (2,8))					      \
      && (!defined __OPTIMIZE_SIZE__ || defined __cplusplus)
      /* The check for __cplusplus allows the use of the builtin, even
 	when optimization for size is on.  This is provided for
@@ -889,7 +890,7 @@ enum
 # endif
 
 /* Return nonzero value if sign of X is negative.  */
-# if __GNUC_PREREQ (6,0)
+# if __GNUC_PREREQ (6,0) || __glibc_clang_prereq (3,3)
 #  define signbit(x) __builtin_signbit (x)
 # elif defined __cplusplus
   /* In C++ mode, __MATH_TG cannot be used, because it relies on
@@ -907,14 +908,16 @@ enum
 # endif
 
 /* Return nonzero value if X is not +-Inf or NaN.  */
-# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+# if (__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__) \
+     || __glibc_clang_prereq (2,8)
 #  define isfinite(x) __builtin_isfinite (x)
 # else
 #  define isfinite(x) __MATH_TG ((x), __finite, (x))
 # endif
 
 /* Return nonzero value if X is neither zero, subnormal, Inf, nor NaN.  */
-# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+# if (__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__) \
+     || __glibc_clang_prereq (2,8)
 #  define isnormal(x) __builtin_isnormal (x)
 # else
 #  define isnormal(x) (fpclassify (x) == FP_NORMAL)
@@ -922,7 +925,8 @@ enum
 
 /* Return nonzero value if X is a NaN.  We could use `fpclassify' but
    we already have this functions `__isnan' and it is faster.  */
-# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+# if (__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__) \
+     || __glibc_clang_prereq (2,8)
 #  define isnan(x) __builtin_isnan (x)
 # else
 #  define isnan(x) __MATH_TG ((x), __isnan, (x))
@@ -939,7 +943,8 @@ enum
 #  define isinf(x) \
     (__builtin_types_compatible_p (__typeof (x), _Float128) \
      ? __isinff128 (x) : __builtin_isinf_sign (x))
-# elif __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+# elif (__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__) \
+       || __glibc_clang_prereq (3,7)
 #  define isinf(x) __builtin_isinf_sign (x)
 # else
 #  define isinf(x) __MATH_TG ((x), __isinf, (x))
-- 
2.17.1