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Re: Patch for PR libgomp/37938, IA64 specific.


On Thu, Nov 06, 2008 at 01:09:44PM -0800, H.J. Lu wrote:
> According to ia64 psABI, ia64 _sync_bool_compare_and_swap should
> have full barrier.  __sync_lock_test_and_set  has acquire barrier.

Ok, then we have just one problematic __sync_lock_test_and_set
in whole libgomp.

Would the following (untested) patch cure it?  Or we can use
__sync_synchronize (); val = __sync_lock_test_and_set (mutex, 0);
if we don't mind mf + xchg4.acq.

--- libgomp/config/linux/ia64/mutex.h.jj	2008-11-06 22:19:11.000000000 +0100
+++ libgomp/config/linux/ia64/mutex.h	2008-11-06 22:22:11.000000000 +0100
@@ -0,0 +1,66 @@
+/* Copyright (C) 2005, 2008 Free Software Foundation, Inc.
+   Contributed by Richard Henderson <rth@redhat.com>.
+
+   This file is part of the GNU OpenMP Library (libgomp).
+
+   Libgomp 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.
+
+   Libgomp 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 libgomp; see the file COPYING.LIB.  If not, write to the
+   Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+   MA 02110-1301, USA.  */
+
+/* As a special exception, if you link this library with other files, some
+   of which are compiled with GCC, to produce an executable, this library
+   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.  */
+
+/* This is a Linux specific implementation of a mutex synchronization
+   mechanism for libgomp.  This type is private to the library.  This
+   implementation uses atomic instructions and the futex syscall.  */
+
+#ifndef GOMP_MUTEX_H
+#define GOMP_MUTEX_H 1
+
+typedef int gomp_mutex_t;
+
+#define GOMP_MUTEX_INIT_0 1
+
+static inline void gomp_mutex_init (gomp_mutex_t *mutex)
+{
+  *mutex = 0;
+}
+
+extern void gomp_mutex_lock_slow (gomp_mutex_t *mutex);
+static inline void gomp_mutex_lock (gomp_mutex_t *mutex)
+{
+  if (!__sync_bool_compare_and_swap (mutex, 0, 1))
+    gomp_mutex_lock_slow (mutex);
+}
+
+extern void gomp_mutex_unlock_slow (gomp_mutex_t *mutex);
+static inline void gomp_mutex_unlock (gomp_mutex_t *mutex)
+{
+  /* On ia64, __sync_lock_test_and_set has acquire semantics,
+     while release semantics is needed for gomp_mutex_unlock.  */
+  int val;
+  __asm__ __volatile__ ("xchg4.rel %0 = [%1], r0;;"
+			: "=r" (val) : "r" (mutex) : "memory");
+  if (__builtin_expect (val > 1, 0))
+    gomp_mutex_unlock_slow (mutex);
+}
+
+static inline void gomp_mutex_destroy (gomp_mutex_t *mutex)
+{
+}
+
+#endif /* GOMP_MUTEX_H */


	Jakub


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