Re: [RFC] How to add vector math functions to Glibc

[Andrew Senkevich <andrew dot n dot senkevich at gmail dot com>]

Hi Joseph,

>> > 4. We need to handle different architectures having different sets of
>> > functions vectorized.
>>
>> We need to have some way for #pragma simd declare to be architecture dependent.
>> It gives possibility to have different sets of vectorized functions
>> for different architectures.
>
> I think having a long series of macros such as __DECL_SIMD_COS_DOUBLE as I
> suggested in <https://sourceware.org/ml/libc-alpha/2014-09/msg00182.html>,
> that the architecture-specific <bits/math-vector.h> header may or may not
> define, would work for this.
>
> The default bits/math-vector.h, for architectures without such functions,
> should be minimal (that is, it should not be necessary to define long
> series of macros for functions you don't have versions of on your
> architecture, so that adding vectorized versions of a new function for one
> architecture doesn't require you to update the files for lots of other
> architectures to say they don't have vectorized versions of that function;
> architecture-independent files should handle the macros possibly not being
> defined).

Is it OK to have following scheme:

diff --git a/bits/math-vector.h b/bits/math-vector.h
new file mode 100644
index 0000000..4a9c786
--- /dev/null
+++ b/bits/math-vector.h
@@ -0,0 +1,21 @@
+/* Platform-specific SIMD declarations for math functions.
+   Copyright (C) 2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never include <bits/math-vector.h> directly; include
<math.h> instead."
+#endif
diff --git a/math/Makefile b/math/Makefile
index 866bc0f..1941b62 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -26,7 +26,7 @@ headers               := math.h bits/mathcalls.h
bits/mathinline.h bits/huge_val.h \
                   bits/huge_valf.h bits/huge_vall.h bits/inf.h bits/nan.h \
                   fpu_control.h complex.h bits/cmathcalls.h fenv.h \
                   bits/fenv.h bits/fenvinline.h bits/mathdef.h tgmath.h \
-                  bits/math-finite.h
+                  bits/math-finite.h bits/math-vector.h

 # FPU support code.
 aux            := setfpucw fpu_control
diff --git a/math/bits/mathcalls.h b/math/bits/mathcalls.h
index ae94990..2d31a11 100644
--- a/math/bits/mathcalls.h
+++ b/math/bits/mathcalls.h
@@ -70,7 +60,15 @@ __MATHCALL (atan,, (_Mdouble_ __x));
 __MATHCALL (atan2,, (_Mdouble_ __y, _Mdouble_ __x));

 /* Cosine of X.  */
+#if !defined _Mfloat_ && !defined _Mlong_double_ && defined __DECL_SIMD_cos
+__DECL_SIMD_cos
+#endif
+#if defined _Mfloat_ && !defined _Mlong_double_ && defined __DECL_SIMD_cosf
+__DECL_SIMD_cosf
+#endif
+#if defined _Mlong_double_ && defined __DECL_SIMD_cosl
+__DECL_SIMD_cosl
+#endif
 __MATHCALL (cos,, (_Mdouble_ __x));
 /* Sine of X.  */
 __MATHCALL (sin,, (_Mdouble_ __x));
diff --git a/math/math.h b/math/math.h
index 72ec2ca..32a7bec 100644
--- a/math/math.h
+++ b/math/math.h
@@ -27,6 +27,9 @@

 __BEGIN_DECLS

+/* Get machine-dependent vector math functions declarations */
+#include <bits/math-vector.h>
+
 /* Get machine-dependent HUGE_VAL value (returned on overflow).
    On all IEEE754 machines, this is +Infinity.  */
 #include <bits/huge_val.h>
diff --git a/sysdeps/x86_64/bits/math-vector.h
b/sysdeps/x86_64/bits/math-vector.h
new file mode 100644
index 0000000..512f4e4
--- /dev/null
+++ b/sysdeps/x86_64/bits/math-vector.h
@@ -0,0 +1,30 @@
+/* SIMD declarations of math functions for x86_64.
+   Copyright (C) 2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never include <bits/math-vector.h> directly; include
<math.h> instead."
+#endif
+
+#if defined _OPENMP && _OPENMP >= 201307
+# define __DECL_SIMD_AVX   _Pragma ("omp declare simd notinbranch
processor(core_3rd_gen_avx)")
+# define __DECL_SIMD_SSE4 _Pragma ("omp declare simd notinbranch
processor(core_i7_sse4_2)")
+
+# define __DECL_SIMD_cos  __DECL_SIMD_AVX
+# define __DECL_SIMD_cosf __DECL_SIMD_SSE4
+#endif

where clause processor() taken from CilkPlus as example, for OpenMP it
is better to discuss - also clause processor or not.