commit 4997e8f31e7415652c3dedec672c0e9bf8caa9ca
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Fri Feb 1 10:39:57 2019 -0200

    math: Enable some math builtins for clang
    
    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.

diff --git a/math/math.h b/math/math.h
index ddee4e408389722f..b3b414f3678e91f7 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))