Comment #7 on issue 2734 by [email protected]: StringDictionary store
is very slow
http://code.google.com/p/v8/issues/detail?id=2734
Those load and store ICs go generic since there are lots of keys coming in.
The generic store IC only supports smi-key based generic stores inline, for
everything else it goes to the runtime.
The generic load IC does directly support unique strings for both fast-mode
objects and dictionaries.
Crankshaft currently doesn't support loads/stores for dictionary maps at
all. Hence they all just go generic (behave identical to the ICs).
This information combined makes the numbers make a lot of sense:
loop1 does 4 accesses (2 loads, 2 stores)
loop2 does 2 accesses (1 load, 1 store) and is double as fast as loop1
loop3 generally only does 1 load; which is handled directly by the IC; so
is a lot faster than loop2.
The first thing we could do is implement a better KeyedStoreIC for the
generic case, that also handles named access. That way we at least avoid
going to the runtime; and, I estimate, should double speed of loop1/2.
Then we could better support keyed access in hydrogen:
* I presume we'd have to have a specific non-generic IC to track this
use-case of accessing objects (and dictionary-mode objects) with multiple
string keys.
* We'd have to not go polymorphic when overwriting a non-normal version of
such IC with a normal version; since I presume the object is first
non-dictionary but then transitions to dictionary mode.
* We probably need a dictionary access implementation in hydrogen that, as
Slava mentioned, first fetches the offset of the element in the dictionary,
and then loads from it or stores to it (if it's already there); so that we
can GVN to optimize this code.
* We probably want to rewrite the keyed stubs in hydrogen rather than doing
this work manually for all platforms; and inline their implementation later
on.
--
You received this message because this project is configured to send all
issue notifications to this address.
You may adjust your notification preferences at:
https://code.google.com/hosting/settings
--
--
v8-dev mailing list
[email protected]
http://groups.google.com/group/v8-dev
---
You received this message because you are subscribed to the Google Groups "v8-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/groups/opt_out.
