From e60a7c39cdcdfd474c4f6cc3b4612870726f55dc Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 25 Oct 2007 10:24:01 +0100
Subject: [PATCH] [cairo-atomic] Check whether we can access int/pointers
 atomically.

Add a configure check to determine whether the host cpu can read/write
cairo_atomic_t without an explicit memory barrier, and update the macros
within cairo-atomic-private.h to reflect this knowledge.
---
 configure.in               | 15 +++++++++++++++
 src/cairo-atomic-private.h | 20 +++++++++++++++-----
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/configure.in b/configure.in
index f85e33c02..7fbe4089f 100644
--- a/configure.in
+++ b/configure.in
@@ -103,6 +103,21 @@ AC_TRY_LINK([int atomic_add(int i) { return __sync_fetch_and_add (&i, 1); }], []
 
 AC_MSG_RESULT([$cairo_atomic_primitives])
 
+AC_MSG_CHECKING([whether atomic ops require a memory barrier])
+case $host_cpu in
+    i?86)
+	cairo_atomic_op_needs_memory_barrier="no"
+	;;
+    *)
+	cairo_atomic_op_needs_memory_barrier="yes"
+	;;
+esac
+if test "x$cairo_atomic_op_needs_memory_barrier" = "xyes"; then
+    AC_DEFINE_UNQUOTED(CAIRO_ATOMIC_OP_NEEDS_MEMORY_BARRIER, 1,
+		       [whether Cairo needs memory barriers around atomic ops])
+fi
+AC_MSG_RESULT([$cairo_atomic_op_needs_memory_barrier])
+
 dnl ===========================================================================
 
 AC_CHECK_LIBM
diff --git a/src/cairo-atomic-private.h b/src/cairo-atomic-private.h
index fbf1d9aea..85fe95626 100644
--- a/src/cairo-atomic-private.h
+++ b/src/cairo-atomic-private.h
@@ -51,9 +51,6 @@ typedef int cairo_atomic_int_t;
 
 # define _cairo_atomic_int_inc(x) ((void) __sync_fetch_and_add(x, 1))
 # define _cairo_atomic_int_dec_and_test(x) (__sync_fetch_and_add(x, -1) == 1)
-# define _cairo_atomic_int_get(x) (*x)
-# define _cairo_atomic_int_set(x, value) ((*x) = value)
-
 # define _cairo_atomic_int_cmpxchg(x, oldv, newv) __sync_val_compare_and_swap (x, oldv, newv)
 
 #else
@@ -70,17 +67,30 @@ _cairo_atomic_int_inc (int *x);
 cairo_private cairo_bool_t
 _cairo_atomic_int_dec_and_test (int *x);
 
+cairo_private int
+_cairo_atomic_int_cmpxchg (int *x, int oldv, int newv);
+
+#endif
+
+
+#ifdef CAIRO_ATOMIC_OP_NEEDS_MEMORY_BARRIER
+
+# include "cairo-compiler-private.h"
+
 cairo_private int
 _cairo_atomic_int_get (int *x);
 
 cairo_private void
 _cairo_atomic_int_set (int *x, int value);
 
-cairo_private int
-_cairo_atomic_int_cmpxchg (int *x, int oldv, int newv);
+#else
+
+# define _cairo_atomic_int_get(x) (*x)
+# define _cairo_atomic_int_set(x, value) ((*x) = value)
 
 #endif
 
+
 #define _cairo_status_set_error(status, err) do { \
     /* hide compiler warnings about cairo_status_t != int (gcc treats its as \
      * an unsigned integer instead, and about ignoring the return value. */  \