460079 - MH_CACHE1 code needs evaluation

Status: VERIFIED INVALID

(Tamarin Graveyard :: Virtual Machine, defect)

Description

[Steven Johnson]

Code was added to MultinameHashtable to add a single-level cache, but in current performance benchmarks it doesn't seem to offer any significant advantages, but does consume memory, so it's been disabled.

We need to revisit it, using the original testcases that prompted its addition (if possible), to see if it's still necessary, or if changes to the interpreter (etc) have made it no longer useful.

Comment 1

[Edwin Smith]

bug 515722 implements a finddef cache that reduces pressure on mnht when called for global lookups, but not property lookups.  If MH_CACHE1 has any effect at all it would be on poorly typed code causing frequent symbol table lookups.  test/performance/v8/*.as are examples of untyped AS3 code.  if they aren't affected by this optimization, we should just remove it.

Comment 2

[Lars T Hansen]

MH_CACHE1 was removed from the VM recently.