Use null instead of undefined for deleted elements in code caches....

Use null instead of undefined for deleted elements in code caches.
Update the lookup and update code for code caches to deal with deleted
elements.

Do not clear the code cache for the builtins object.  If there was a
matching element in the code cache, we would have hit the monomorphic
prototype failure case and removed it.

Committed: http://code.google.com/p/v8/source/detail?r=340

[Kasper Lund, 2008-09-18 10:56:22]

LGTM, but it could use a few extra comments and there seems to be something
fishy going on if deleted_index is 0. This should probably be addressed before
you submit.

http://codereview.chromium.org/3140/diff/1/2
File src/objects.cc (right):

http://codereview.chromium.org/3140/diff/1/2#newcode2390
Line 2390: if (deleted_index > 0) i = deleted_index;
What if deleted_index is 0? Shouldn't you use that slot then?

http://codereview.chromium.org/3140/diff/1/2#newcode2406
Line 2406: if (deleted_index > 0) {
How about reusing if deleted_index is 0? Isn't that the right thing to do?

http://codereview.chromium.org/3140/diff/1/2#newcode2432
Line 2432: if (key->IsNull()) {
Maybe add a comment here that explains that we're skipping deleted entries?

http://codereview.chromium.org/3140/diff/1/2#newcode2460
Line 2460: array->set_null(index - 1);  // key
Add comment that explains that deleted entries are dealt with specially when
looking up in the cache so they can't be undefined (must be null).

[Mads Ager (chromium), 2008-09-18 11:17:49]

Thanks.  Fixed.