Re: [PATCH][PING] Inline C99 math functions

["Carlos O'Donell" <carlos at redhat dot com>]

On 07/13/2015 11:11 AM, Wilco Dijkstra wrote:
>> 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?
 
This looks good to me for 2.23, it is not OK for 2.22.

Please wait until after 2.23 opens and until after you commit the benchmark.

Cheers,
Carlos.

> ---
>  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
>