[PATCH][PING] Inline C99 math functions

["Wilco Dijkstra" <wdijkstr at arm dot com>]

> Wilco Dijkstra wrote:
> Add inlining of the C99 math functions isinf/isnan/signbit/isfinite/isnormal/fpclassify using
> GCC built-ins when available. Since going through the PLT is expensive for these small
> functions, inlining results in major speedups (about 7x on Cortex-A57 for isinf). The GCC
> built-ins are not correct if signalling NaN support is required, and thus are turned off in
> that case (see GCC bug 66462). The test-snan.c tests sNaNs and so must be explicitly built
> with -fsignaling-nans.
> 
> As a result of this many target overrides and the various __isnan/__finite inlines in
> math_private.h are no longer required. If agreed we could remove all this code and only keep
> the generic definition of isinf/etc which will use the builtin.
> 
> Tested on AArch64. OK for commit?
> 
> ChangeLog:
> 2015-06-15  Wilco Dijkstra  <wdijkstr@arm.com>
> 
> 	* math/Makefile: Build test-snan.c with -fsignaling-nans.
> 	* math/math.h (fpclassify): Use __builtin_fpclassify when
> 	available.  (signbit): Use __builtin_signbit(f/l).
> 	(isfinite): Use__builtin_isfinite.  (isnormal): Use
> 	__builtin_isnormal.  (isnan): Use __builtin_isnan.
> 	(isinf): Use __builtin_isinf_sign.

As suggested __fpclassify is not inlined when optimizing for size, and a benchmark
has been created (json output for x64 attached showing the large gains due to inlining).

OK for commit?


---
 math/Makefile |  1 +
 math/math.h   | 51 ++++++++++++++++++++++++++++++---------------------
 2 files changed, 31 insertions(+), 21 deletions(-)

diff --git a/math/Makefile b/math/Makefile
index 9a3cf32..f78d75b 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -155,6 +155,7 @@ CFLAGS-test-tgmath.c = -fno-builtin
 CFLAGS-test-tgmath2.c = -fno-builtin
 CFLAGS-test-tgmath-ret.c = -fno-builtin
 CFLAGS-test-powl.c = -fno-builtin
+CFLAGS-test-snan.c = -fsignaling-nans
 CPPFLAGS-test-ifloat.c = -U__LIBC_INTERNAL_MATH_INLINES -D__FAST_MATH__ \
 			 -DTEST_FAST_MATH -fno-builtin
 CPPFLAGS-test-idouble.c = -U__LIBC_INTERNAL_MATH_INLINES -D__FAST_MATH__ \
diff --git a/math/math.h b/math/math.h
index 22f0989..1721118 100644
--- a/math/math.h
+++ b/math/math.h
@@ -215,8 +215,15 @@ enum
       FP_NORMAL
   };
 
+/* GCC bug 66462 means we cannot use the math builtins with -fsignaling-nan,
+   so disable builtins if this is enabled.  When fixed in a newer GCC,
+   the __SUPPORT_SNAN__ check may be skipped for those versions.  */
+
 /* Return number of classification appropriate for X.  */
-# ifdef __NO_LONG_DOUBLE_MATH
+# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__ && !defined __OPTIMIZE_SIZE__
+#  define fpclassify(x) __builtin_fpclassify (FP_NAN, FP_INFINITE,	      \
+     FP_NORMAL, FP_SUBNORMAL, FP_ZERO, x)
+# elif defined __NO_LONG_DOUBLE_MATH
 #  define fpclassify(x) \
      (sizeof (x) == sizeof (float) ? __fpclassifyf (x) : __fpclassify (x))
 # else
@@ -229,32 +236,26 @@ enum
 
 /* Return nonzero value if sign of X is negative.  */
 # if __GNUC_PREREQ (4,0)
-#  ifdef __NO_LONG_DOUBLE_MATH
-#   define signbit(x) \
-     (sizeof (x) == sizeof (float) \
-      ? __builtin_signbitf (x) : __builtin_signbit (x))
-#  else
-#   define signbit(x) \
-     (sizeof (x) == sizeof (float)                                            \
-      ? __builtin_signbitf (x)                                                        \
-      : sizeof (x) == sizeof (double)                                         \
+#  define signbit(x) \
+     (sizeof (x) == sizeof (float)					      \
+      ? __builtin_signbitf (x)						      \
+      : sizeof (x) == sizeof (double)					      \
       ? __builtin_signbit (x) : __builtin_signbitl (x))
-# endif
-# else
-#  ifdef __NO_LONG_DOUBLE_MATH
-#   define signbit(x) \
+# elif defined __NO_LONG_DOUBLE_MATH
+#  define signbit(x) \
      (sizeof (x) == sizeof (float) ? __signbitf (x) : __signbit (x))
-#  else
-#   define signbit(x) \
+# else
+#  define signbit(x) \
      (sizeof (x) == sizeof (float)					      \
       ? __signbitf (x)							      \
       : sizeof (x) == sizeof (double)					      \
       ? __signbit (x) : __signbitl (x))
-#  endif
 # endif
 
 /* Return nonzero value if X is not +-Inf or NaN.  */
-# ifdef __NO_LONG_DOUBLE_MATH
+# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+#  define isfinite(x) __builtin_isfinite (x)
+# elif defined __NO_LONG_DOUBLE_MATH
 #  define isfinite(x) \
      (sizeof (x) == sizeof (float) ? __finitef (x) : __finite (x))
 # else
@@ -266,11 +267,17 @@ enum
 # endif
 
 /* Return nonzero value if X is neither zero, subnormal, Inf, nor NaN.  */
-# define isnormal(x) (fpclassify (x) == FP_NORMAL)
+# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+#  define isnormal(x) __builtin_isnormal (x)
+# else
+#  define isnormal(x) (fpclassify (x) == FP_NORMAL)
+# endif
 
 /* Return nonzero value if X is a NaN.  We could use `fpclassify' but
    we already have this functions `__isnan' and it is faster.  */
-# ifdef __NO_LONG_DOUBLE_MATH
+# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+#  define isnan(x) __builtin_isnan (x)
+# elif defined __NO_LONG_DOUBLE_MATH
 #  define isnan(x) \
      (sizeof (x) == sizeof (float) ? __isnanf (x) : __isnan (x))
 # else
@@ -282,7 +289,9 @@ enum
 # endif
 
 /* Return nonzero value if X is positive or negative infinity.  */
-# ifdef __NO_LONG_DOUBLE_MATH
+# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__
+#  define isinf(x) __builtin_isinf_sign (x)
+# elif defined __NO_LONG_DOUBLE_MATH
 #  define isinf(x) \
      (sizeof (x) == sizeof (float) ? __isinff (x) : __isinf (x))
 # else
-- 
1.9.1

Attachment: bench-math-inlines.out
Description: Binary data