Shrink "struct object" a bit

This shrinks "struct object" by a small amount, by getting rid of the
"struct type *" pointer and replacing it with a 3-bit bitfield instead.

In addition, we merge the bitfields and the "flags" field, which
incidentally should also remove a useless 4-byte padding from the object
when in 64-bit mode.

Now, our "struct object" is still too damn large, but it's now less
obviously bloated, and of the remaining fields, only the "util" (which is
not used by most things) is clearly something that should be eventually
discarded.

This shrinks the "git-rev-list --all" memory use by about 2.5% on the
kernel archive (and, perhaps more importantly, on the larger mozilla
archive). That may not sound like much, but I suspect it's more on a
64-bit platform.

There are other remaining inefficiencies (the parent lists, for example,
probably have horrible malloc overhead), but this was pretty obvious.

Most of the patch is just changing the comparison of the "type" pointer
from one of the constant string pointers to the appropriate new TYPE_xxx
small integer constant.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 18 insertions, 2 deletions

diff --git a/object.h b/object.h
index e08afbd29f..a0762b6672 100644
--- a/object.h
+++ b/object.h
@@ -12,12 +12,22 @@ struct object_refs {
 	struct object *ref[FLEX_ARRAY]; /* more */
 };
 
+#define TYPE_BITS   3
+#define FLAG_BITS  27
+
+#define TYPE_NONE   0
+#define TYPE_BLOB   1
+#define TYPE_TREE   2
+#define TYPE_COMMIT 3
+#define TYPE_TAG    4
+#define TYPE_BAD    5
+
 struct object {
 	unsigned parsed : 1;
 	unsigned used : 1;
-	unsigned int flags;
+	unsigned type : TYPE_BITS;
+	unsigned flags : FLAG_BITS;
 	unsigned char sha1[20];
-	const char *type;
 	struct object_refs *refs;
 	void *util;
 };
@@ -25,6 +35,12 @@ struct object {
 extern int track_object_refs;
 extern int obj_allocs;
 extern struct object **objs;
+extern const char *type_names[];
+
+static inline const char *typename(unsigned int type)
+{
+	return type_names[type > TYPE_TAG ? TYPE_BAD : type];
+}
 
 /** Internal only **/
 struct object *lookup_object(const unsigned char *sha1);