Add marking of an instance as having been weakly referenced.

Source/GSPrivate.h

@@ -641,6 +641,7 @@ GSPrivateEncodeBase64(const uint8_t *src, NSUInteger length, uint8_t *dst)
 /* When we don't have a runtime with ARC to support weak references, we
  * use our own version.
  */
+BOOL GSPrivateMarkedWeak(id obj, BOOL  mark) GS_ATTRIB_PRIVATE;
 void GSWeakInit() GS_ATTRIB_PRIVATE;
 BOOL objc_delete_weak_refs(id obj);
 #endif

Source/NSObject.m

@@ -208,15 +208,23 @@ extern void GSLogZombie(id o, SEL sel)
 #undef	GSATOMICREAD
 #endif
 
-#if defined(__llvm__) || (defined(USE_ATOMIC_BUILTINS) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1)))
-/* Use the GCC atomic operations with recent GCC versions */
+#ifdef OBJC_CAP_ARC
 
 typedef intptr_t volatile *gsatomic_t;
 typedef intptr_t gsrefcount_t;
 #define GSATOMICREAD(X) (*(X))
 #define GSAtomicIncrement(X)    __sync_add_and_fetch(X, 1)
 #define GSAtomicDecrement(X)    __sync_sub_and_fetch(X, 1)
 
+#elif (defined(USE_ATOMIC_BUILTINS) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1)))
+/* Use the GCC atomic operations with recent GCC versions */
+
+typedef int32_t volatile *gsatomic_t;
+typedef int32_t gsrefcount_t;
+#define GSATOMICREAD(X) (*(X))
+#define GSAtomicIncrement(X)    __sync_add_and_fetch(X, 1)
+#define GSAtomicDecrement(X)    __sync_sub_and_fetch(X, 1)
+
 #elif	defined(_WIN32)
 
 /* Set up atomic read, increment and decrement for mswindows
@@ -382,7 +390,7 @@ __asm__ __volatile__ (
 
 #include <pthread.h>
 
-typedef int     gsrefcount_t;   // No atomics, use a simple integer
+typedef int32_t	gsrefcount_t;   // No atomics, use a simple integer
 
 /* Having just one allocationLock for all leads to lock contention
  * if there are lots of threads doing lots of retain/release calls.
@@ -415,12 +423,21 @@ __asm__ __volatile__ (
 #endif
 #define alignof(type) __builtin_offsetof(struct { const char c; type member; }, member)
 
+#ifndef OBJC_CAP_ARC
+typedef struct {
+  BOOL	hadWeakReference: 1;	// set if the instance ever had a weak reference
+} gsinstinfo_t;
+#endif
+
 /*
  *	Define a structure to hold information that is held locally
  *	(before the start) in each object.
  */
 typedef struct obj_layout_unpadded {
   gsrefcount_t	retained;
+#ifndef OBJC_CAP_ARC
+  gsinstinfo_t	extra;
+#endif
 } unp;
 #define	UNP sizeof(unp)
 
@@ -441,9 +458,26 @@ __asm__ __volatile__ (
   char	padding[__BIGGEST_ALIGNMENT__ - ((UNP % __BIGGEST_ALIGNMENT__)
     ? (UNP % __BIGGEST_ALIGNMENT__) : __BIGGEST_ALIGNMENT__)];
   gsrefcount_t	retained;
+#ifndef OBJC_CAP_ARC
+  gsinstinfo_t	extra;
+#endif
 };
 typedef	struct obj_layout *obj;
 
+#ifndef OBJC_CAP_ARC
+BOOL
+GSPrivateMarkedWeak(id anObject, BOOL  mark)
+{
+  BOOL	wasMarked = ((obj)anObject)[-1].extra.hadWeakReference;
+
+  if (mark)
+    {
+      ((obj)anObject)[-1].extra.hadWeakReference = YES;
+    }
+  return wasMarked;
+}
+#endif
+
 /*
  * These symbols are provided by newer versions of the GNUstep Objective-C
  * runtime.  When linked against an older version, we will use our internal

Source/ObjectiveC2/weak.m

@@ -171,6 +171,11 @@
   GSIMapKey	key;
   GSIMapBucket  bucket;
   WeakRef 	*ref;
+
+  /* Mark the instance as having had a weak reference at some point.
+   * This information is used when the instance is deallocated.
+   */
+  GSPrivateMarkedWeak(obj, YES);
 
   key.obj = obj;
   bucket = GSIMapBucketForKey(&weakRefs, key);
@@ -254,11 +259,11 @@
   GSIMapBucket  bucket;
   WeakRef 	*ref;
 
-  /* FIXME ... for performance we should have marked the object as having
-   * weak references and we should check that in order to avoid the cost
+  /* For performance we should have marked the object as having
+   * weak references and we check that in order to avoid the cost
    * of the map table lookup when it's not needed.
    */
-  if (0)
+  if (NO == GSPrivateMarkedWeak(obj, NO))
     {
       return NO;
     }