Move math_opt_barrier, math_force_eval to separate math-barriers.h.

This patch continues cleaning up math_private.h by moving the
math_opt_barrier and math_force_eval macros to a separate header
math-barriers.h.

At present, those macros are inside a "#ifndef math_opt_barrier" in
math_private.h to allow architectures to override them and then use
a separate math-barriers.h header, no such #ifndef or #include_next is
needed; architectures just have their own alternative version of
math-barriers.h when providing their own optimized versions that avoid
going through memory unnecessarily.  The generic math-barriers.h has a
comment added to document these two macros.

In this patch, math_private.h is made to #include <math-barriers.h>,
so files using these macros do not need updating yet.  That is because
of uses of math_force_eval in math_check_force_underflow and
math_check_force_underflow_nonneg, which are still defined in
math_private.h.  Once those are moved out to a separate header, that
separate header can be made to include <math-barriers.h>, as can the
other files directly using these barrier macros, and then the include
of <math-barriers.h> from math_private.h can be removed.

Tested for x86_64 and x86.  Also tested with build-many-glibcs.py that
installed stripped shared libraries are unchanged by this patch.

	* sysdeps/generic/math-barriers.h: New file.
	* sysdeps/generic/math_private.h [!math_opt_barrier]
	(math_opt_barrier): Move to math-barriers.h.
	[!math_opt_barrier] (math_force_eval): Likewise.
	* sysdeps/aarch64/fpu/math-barriers.h: New file.
	* sysdeps/aarch64/fpu/math_private.h (math_opt_barrier): Move to
	math-barriers.h.
	(math_force_eval): Likewise.
	* sysdeps/alpha/fpu/math-barriers.h: New file.
	* sysdeps/alpha/fpu/math_private.h (math_opt_barrier): Move to
	math-barriers.h.
	(math_force_eval): Likewise.
	* sysdeps/x86/fpu/math-barriers.h: New file.
	* sysdeps/i386/fpu/fenv_private.h (math_opt_barrier): Move to
	math-barriers.h.
	(math_force_eval): Likewise.
	* sysdeps/m68k/m680x0/fpu/math_private.h: Move to....
	* sysdeps/m68k/m680x0/fpu/math-barriers.h: ... here.  Adjust
	multiple-include guard for rename.
	* sysdeps/powerpc/fpu/math-barriers.h: New file.
	* sysdeps/powerpc/fpu/math_private.h (math_opt_barrier): Move to
	math-barriers.h.
	(math_force_eval): Likewise.

1 files changed, 37 insertions, 0 deletions

diff --git a/sysdeps/generic/math-barriers.h b/sysdeps/generic/math-barriers.h
new file mode 100644
index 0000000000..425173149c
--- /dev/null
+++ b/sysdeps/generic/math-barriers.h
@@ -0,0 +1,37 @@
+/* Control when floating-point expressions are evaluated.  Generic version.
+   Copyright (C) 2007-2018 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_BARRIERS_H
+#define _MATH_BARRIERS_H	1
+
+/* math_opt_barrier evaluates and returns its floating-point argument
+   and ensures that the evaluation of any expression using the result
+   of math_opt_barrier is not moved before the call.  math_force_eval
+   ensures that its floating-point argument is evaluated for its side
+   effects even if its value is apparently unused, and that the
+   evaluation of its argument is not moved after the call.  Both these
+   macros are used to ensure the correct ordering of floating-point
+   expression evaluations with respect to accesses to the
+   floating-point environment.  */
+
+#define math_opt_barrier(x)					\
+  ({ __typeof (x) __x = (x); __asm ("" : "+m" (__x)); __x; })
+#define math_force_eval(x)						\
+  ({ __typeof (x) __x = (x); __asm __volatile__ ("" : : "m" (__x)); })
+
+#endif /* math-barriers.h */