The JSC JIT emits stubs to cache get_by_id prototype accesses. The DFG JIT does not implement this optimization.
Created attachment 99963 [details] the patch
Comment on attachment 99963 [details] the patch I think there might be an alternative given the way we're currently code generating the self accesses. We may be able to plant a couple of extra instructions inline in the JIT code to load to prototype & check its structure, immediately prior to the load. But this is just a possible idea to explore - patch as is looks fine.
Comment on attachment 99963 [details] the patch Clearing flags on attachment: 99963 Committed r90601: <http://trac.webkit.org/changeset/90601>
All reviewed patches have been landed. Closing bug.
Reopening - these changes were rolled out in r90673 due to https://bugs.webkit.org/show_bug.cgi?id=64181
Closing, I think these changes were landed as a part of another bug. Filip, please reopen if I'm mistaken & this is still a live issue.