[Bug 445818] Using explicit assembly to implement compare-and-swap on x86-64 to avoid __sync_bool_compare_and_swap (GCC intrinsic) as the latter is buggy at least on ARM. r=brendan

js/src/jslock.cpp

@@ -120,6 +120,23 @@ NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
     return (int)res;
 }
 
+#elif defined(__GNUC__) && defined(__x86_64__)
+static JS_INLINE int
+NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
+{
+    unsigned int res;
+
+    __asm__ __volatile__ (
+                          "lock\n"
+                          "cmpxchgq %2, (%1)\n"
+                          "sete %%al\n"
+                          "movzbl %%al, %%eax\n"
+                          : "=a" (res)
+                          : "r" (w), "r" (nv), "a" (ov)
+                          : "cc", "memory");
+    return (int)res;
+}
+
 #elif defined(SOLARIS) && defined(sparc) && defined(ULTRA_SPARC)
 
 static JS_INLINE int
@@ -174,15 +191,6 @@ NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
     return !__kernel_cmpxchg(ov, nv, vp);
 }
 
-#elif defined(__GNUC__) &&                                                    \
-    (__GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1))
-
-static JS_INLINE int
-NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
-{
-    return __sync_bool_compare_and_swap(w, ov, nv);
-}
-
 #else
 
 #error "JS_HAS_NATIVE_COMPARE_AND_SWAP should be 0 if your platform lacks a compare-and-swap instruction."

js/src/jslock.h

@@ -56,11 +56,10 @@ JS_BEGIN_EXTERN_C
 
 #if (defined(_WIN32) && defined(_M_IX86)) ||                                  \
     (defined(__GNUC__) && defined(__i386__)) ||                               \
+    (defined(__GNUC__) && defined(__x86_64__)) ||                             \
     (defined(SOLARIS) && defined(sparc) && defined(ULTRA_SPARC)) ||           \
     defined(AIX) ||                                                           \
-    defined(USE_ARM_KUSER) ||                                                 \
-    (defined(__GNUC__) &&                                                     \
-     (__GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1)))
+    defined(USE_ARM_KUSER)
 # define JS_HAS_NATIVE_COMPARE_AND_SWAP 1
 #else
 # define JS_HAS_NATIVE_COMPARE_AND_SWAP 0