PATCH (libstdc++-v3 3.3): Re-enable i386/atomicity.h

[Loren James Rittle <rittle at latour dot rsch dot comm dot mot dot com>]

> This patch has seen enough eyes to warrant mainline installation thus
> now committed.  It is believed to work in all configurations of an
> IA32 system including SMP.  We shall give it some time on mainline and
> I will file a PR against 3.3 RE the issue.

Mark, tested against 3.3 branch on i386-unknown-freebsd4.8 without
regression and similar great speedup noted.  For the record, there is
still a bone of contention (and lack of knowledge of the current
situation, i.e. I can find no test case that actually fails) regarding
code built by an i386-*-<os> compiler interoperating with a C++
library built by an i486-*-<os> compiler and vice versa.  I think we
can all agree this is something to think deeper about and address for
3.4.  This patch makes no change in the status of this point (i.e. if
that is broken before this new file, it is broken after in the
precisely same manner).  OK for 3.3 branch (in order to avoid shipping
widely-used i386 configurations pointing to generic/atomicity.h)?

2003-05-01 Joel Sherrill  <joel.sherrill@OARcorp.com>
	   Loren J. Rittle <ljrittle@acm.org>
	   Martin v. Loewis  <martin@v.loewis.de>

	libstdc++/10556
	* config/cpu/i386/atomicity.h: New file.

Index: libstdc++-v3/config/cpu/i386/atomicity.h
===================================================================
RCS file: libstdc++-v3/config/cpu/i386/atomicity.h
diff -N libstdc++-v3/config/cpu/i386/atomicity.h
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- libstdc++-v3/config/cpu/i386/atomicity.h	29 Apr 2003 21:08:52 -0000
***************
*** 0 ****
--- 1,75 ----
+ // Low-level functions for atomic operations: x86, x >= 3 version  -*- C++ -*-
+ 
+ // Copyright (C) 2003 Free Software Foundation, Inc.
+ //
+ // This file is part of the GNU ISO C++ Library.  This library is free
+ // software; you can redistribute it and/or modify it under the
+ // terms of the GNU General Public License as published by the
+ // Free Software Foundation; either version 2, or (at your option)
+ // any later version.
+ 
+ // This 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 General Public License for more details.
+ 
+ // You should have received a copy of the GNU General Public License along
+ // with this library; see the file COPYING.  If not, write to the Free
+ // Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+ // USA.
+ 
+ // As a special exception, you may use this file as part of a free software
+ // library without restriction.  Specifically, if other files instantiate
+ // templates or use macros or inline functions from this file, or you compile
+ // this file and link it with other files to produce an executable, this
+ // file does not by itself cause the resulting executable to be covered by
+ // the GNU General Public License.  This exception does not however
+ // invalidate any other reasons why the executable file might be covered by
+ // the GNU General Public License.
+ 
+ #ifndef _BITS_ATOMICITY_H
+ #define _BITS_ATOMICITY_H	1
+ 
+ typedef int _Atomic_word;
+ 
+ template <int __inst>
+ struct __Atomicity_lock
+ {
+   static volatile _Atomic_word _S_atomicity_lock;
+ };
+ 
+ template <int __inst>
+ volatile _Atomic_word __Atomicity_lock<__inst>::_S_atomicity_lock = 0;
+ 
+ template volatile _Atomic_word __Atomicity_lock<0>::_S_atomicity_lock;
+ 
+ static inline _Atomic_word 
+ __attribute__ ((__unused__))
+ __exchange_and_add (volatile _Atomic_word *__mem, int __val)
+ {
+   register _Atomic_word __result, __tmp = 1;
+ 
+   /* obtain the atomic exchange/add spin lock */
+   do {
+     __asm__ __volatile__ ("xchgl %0,%1"
+ 			  : "+m" (__Atomicity_lock<0>::_S_atomicity_lock),
+ 			    "+r" (__tmp));
+   } while (__tmp);
+ 
+   __result = *__mem;
+   *__mem += __val;
+ 
+   /* release spin lock */
+   __Atomicity_lock<0>::_S_atomicity_lock = 0;
+ 
+   return __result;
+ }
+ 
+ static inline void
+ __attribute__ ((__unused__))
+ __atomic_add (volatile _Atomic_word* __mem, int __val)
+ {
+   __exchange_and_add (__mem, __val);
+ }
+ 
+ #endif /* atomicity.h */