2010-05-29 Mark Probst <mark.probst@gmail.com>

	* sgen-gc.c: Always use DESC_TYPE_RUN_LENGTH for objects without
	references so that we don't have to do the cache-cold fetch of the
	class in copy_object_no_checks().

svn path=/trunk/mono/; revision=158137

2 files changed, 16 insertions, 1 deletions

diff --git a/mono/metadata/ChangeLog b/mono/metadata/ChangeLog
index 2008db857ed..73b8cdc3c27 100644
--- a/mono/metadata/ChangeLog
+++ b/mono/metadata/ChangeLog
@@ -1,3 +1,9 @@
+2010-05-29  Mark Probst  <mark.probst@gmail.com>
+
+	* sgen-gc.c: Always use DESC_TYPE_RUN_LENGTH for objects without
+	references so that we don't have to do the cache-cold fetch of the
+	class in copy_object_no_checks().
+
 2010-05-29  Robert Jordan  <robertj@gmx.net>
 
 	* marshal.c (mono_marshal_asany): marshal LPWSTRs using
diff --git a/mono/metadata/sgen-gc.c b/mono/metadata/sgen-gc.c
index bcde5c4c70b..9718c176057 100644
--- a/mono/metadata/sgen-gc.c
+++ b/mono/metadata/sgen-gc.c
@@ -1101,6 +1101,12 @@ enum {
 	 * We don't use 0 so that 0 isn't a valid GC descriptor.  No
 	 * deep reason for this other than to be able to identify a
 	 * non-inited descriptor for debugging.
+	 *
+	 * If an object contains no references, its GC descriptor is
+	 * always DESC_TYPE_RUN_LENGTH, without a size, no exceptions.
+	 * This is so that we can quickly check for that in
+	 * copy_object_no_checks(), without having to fetch the
+	 * object's class.
 	 */
 	DESC_TYPE_RUN_LENGTH = 1, /* 15 bits aligned byte size | 1-3 (offset, numptr) bytes tuples */
 	DESC_TYPE_SMALL_BITMAP, /* 15 bits aligned byte size | 16-48 bit bitmap */
@@ -1281,6 +1287,9 @@ mono_gc_make_descr_for_array (int vector, gsize *elem_bitmap, int numbits, size_
 			num_set++;
 		}
 	}
+	/* See comment at the definition of DESC_TYPE_RUN_LENGTH. */
+	if (first_set < 0)
+		return DESC_TYPE_RUN_LENGTH;
 	if (elem_size <= MAX_ELEMENT_SIZE) {
 		desc |= elem_size << VECTOR_ELSIZE_SHIFT;
 		if (!num_set) {
@@ -2091,7 +2100,7 @@ copy_object_no_checks (void *obj)
 	mword objsize;
 	char *destination;
 	MonoVTable *vt = ((MonoObject*)obj)->vtable;
-	gboolean has_references = vt->klass->has_references;
+	gboolean has_references = vt->gc_descr != DESC_TYPE_RUN_LENGTH;
 
 	objsize = safe_object_get_size ((MonoObject*)obj);
 	objsize += ALLOC_ALIGN - 1;