Enable correct behaviour with respect to ARC for objc_{g,s}etIvar().

Test/CMakeLists.txt

@@ -25,6 +25,7 @@ set(TESTS
 	RuntimeTest.m
 	WeakBlock_arc.m
 	WeakReferences_arc.m
+	ivar_arc.m
 	objc_msgSend.m
 	msgInterpose.m
 	NilException.m

Test/ivar_arc.m

@@ -0,0 +1,52 @@
+#include "Test.h"
+#include "../objc/runtime.h"
+
+@interface Foo : Test
+{
+	@public
+	__weak id w;
+	__unsafe_unretained id u;
+	__strong id s;
+}
+@end
+@implementation Foo @end
+@interface Dealloc : Test
+@end
+int dealloc = 0;
+@implementation Dealloc
+- (void)dealloc
+{
+	dealloc++;
+}
+@end
+
+void setIvar(id obj, const char * name, id val)
+{
+	object_setIvar(obj, class_getInstanceVariable(object_getClass(obj), name), val);
+}
+
+int main(void)
+{
+	Foo *f = [Foo new];
+	Dealloc *d = [Dealloc new];
+	__unsafe_unretained Dealloc *dead;
+	setIvar(f, "w", d);
+	assert(f->w == d);
+	assert(dealloc == 0);
+	d = 0;
+	assert(dealloc == 1);
+	assert(f->w == nil);
+	dealloc = 0;
+	d = [Dealloc new];
+	dead = d;
+	setIvar(f, "s", d);
+	assert(dealloc == 0);
+	assert(f->s == d);
+	d = nil;
+	assert(dealloc == 0);
+	assert(f->s == dead);
+	setIvar(f, "s", nil);
+	assert(dealloc == 1);
+	assert(f->s == nil);
+	return 0;
+}

class.h

@@ -18,6 +18,24 @@ struct objc_bitfield
 	int32_t values[0];
 };
 
+static inline BOOL objc_bitfield_test(uintptr_t bitfield, uint64_t field)
+{
+	if (bitfield & 1)
+	{
+		uint64_t bit = 1<<(field+1);
+		return (bitfield & bit) == bit;
+	}
+	struct objc_bitfield *bf = (struct objc_bitfield*)bitfield;
+	uint64_t byte = field / 32;
+	if (byte >= bf->length)
+	{
+		return NO;
+	}
+	uint64_t bit = 1<<(field%32);
+	return (bf->values[byte] & bit) == bit;
+}
+
+
 struct objc_class
 {
 	/**
@@ -141,13 +159,13 @@ struct objc_class
 	 * bits are set, from low to high, for each ivar in the object that is a
 	 * strong pointer.
 	 */
-	intptr_t                   strong_pointers;
+	uintptr_t                  strong_pointers;
 	/**
 	 * The location of all zeroing weak pointer ivars declared by this class.
 	 * The format of this field is the same as the format of the
 	 * strong_pointers field.
 	 */
-	intptr_t                   weak_pointers;
+	uintptr_t                  weak_pointers;
 };
 
 /**

ivar.c

@@ -2,6 +2,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include "objc/runtime.h"
+#include "objc/objc-arc.h"
 #include "class.h"
 #include "ivar.h"
 #include "visibility.h"
@@ -143,18 +144,69 @@ PRIVATE void objc_compute_ivar_offsets(Class class)
 	}
 }
 
+typedef enum {
+	ownership_invalid,
+	ownership_strong,
+	ownership_weak,
+	ownership_unsafe
+} ownership;
+
+ownership ownershipForIvar(Class cls, Ivar ivar)
+{
+	struct objc_ivar_list *list = cls->ivars;
+	if ((ivar < list->ivar_list) || (ivar >= &list->ivar_list[list->count]))
+	{
+		// Try the superclass
+		if (cls->super_class)
+		{
+			return ownershipForIvar(cls->super_class, ivar);
+		}
+		return ownership_invalid;
+	}
+	if (!objc_test_class_flag(cls, objc_class_flag_new_abi))
+	{
+		return ownership_unsafe;
+	}
+	if (cls->abi_version < 1)
+	{
+		return ownership_unsafe;
+	}
+	if (objc_bitfield_test(cls->strong_pointers, (ivar - list->ivar_list)))
+	{
+		return ownership_strong;
+	}
+	if (objc_bitfield_test(cls->weak_pointers, (ivar - list->ivar_list)))
+	{
+		return ownership_weak;
+	}
+	return ownership_unsafe;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Public API functions
 ////////////////////////////////////////////////////////////////////////////////
 
 void object_setIvar(id object, Ivar ivar, id value)
 {
-	char *addr = (char*)object;
-	addr += ivar_getOffset(ivar);
-	// FIXME: ARC ownership!  We don't have enough information to do this
-	// correctly with the current ABI.  We need to fix it with the next ABI
-	// bump.
-	*(id*)addr = value;
+	ownershipForIvar(object_getClass(object), ivar);
+	id *addr = (id*)((char*)object + ivar_getOffset(ivar));
+	switch (ownershipForIvar(object_getClass(object), ivar))
+	{
+		case ownership_strong:
+			objc_storeStrong(addr, value);
+			break;
+		case ownership_weak:
+			objc_storeWeak(addr, value);
+			break;
+		case ownership_unsafe:
+			*addr = value;
+			break;
+		case ownership_invalid:
+#ifndef NDEBUG
+			fprintf(stderr, "Ivar does not belong to this class!\n");
+#endif
+			break;
+	}
 }
 
 Ivar object_setInstanceVariable(id obj, const char *name, void *value)
@@ -174,7 +226,23 @@ Ivar object_setInstanceVariable(id obj, const char *name, void *value)
 
 id object_getIvar(id object, Ivar ivar)
 {
-	return *(id*)(((char*)object) + ivar_getOffset(ivar));
+	ownershipForIvar(object_getClass(object), ivar);
+	id *addr = (id*)((char*)object + ivar_getOffset(ivar));
+	switch (ownershipForIvar(object_getClass(object), ivar))
+	{
+		case ownership_strong:
+			return objc_retainAutoreleaseReturnValue(*addr);
+		case ownership_weak:
+			return objc_loadWeak(addr);
+			break;
+		case ownership_unsafe:
+			return *addr;
+		case ownership_invalid:
+#ifndef NDEBUG
+			fprintf(stderr, "Ivar does not belong to this class!\n");
+#endif
+		return nil;
+	}
 }
 
 Ivar object_getInstanceVariable(id obj, const char *name, void **outValue)