1323306 - Break the weak marking phase into finer-grained buckets

Status: NEW

(Core :: JavaScript: GC, defect, P3)

Description

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

One thing I noticed in bug 1314828 is that we spend about as much time in PHASE_SWEEP_MARK_WEAK and we do in PHASE_SWEEP_MARK_GRAY_WEAK. That's pretty weird since we expect to have a lot fewer gray objects than black objects in general. If we could figure out what sort of objects are getting marked gray via weak marking, we might discover some interesting inefficiencies. I suspect the debugger may be causing stuff to be marked gray when it shouldn't be marked at all, but who knows.

One way to gain insight here is to break up the weak marking phase into WeakMap marking, debugger marking, JIT code marking, etc. That's what this bug is about.