511040 - NJ: flesh out the hashtable in nanojit/Containers.h a bit

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Graydon Hoare :graydon]

Attachment: Brand new shiny bits

The nanojit allocator-based hashtable type has some implementation inefficiencies (it takes and returns by-value structures, where it could use const &), and limits itself to int32_t for no reason I can see, and also doesn't handle general key types.

The attached patch fixes these issues. The provided general-purpose hash is murmurhash 2, a relatively fast word-based one popular these days among the cool kids. It's done as a template parameter on the hashtable so we can use different ones too (I'm intending to use different ones for the JIT cache tables that are replacing Fragmento).

Comment 1

[Edwin Smith]

any profile data? in other cases we've specialized the hash function for one-word (pointer) values, and most if not all current uses of HashMap fit this pattern, using either NIns* or LIns* as keys.  This is also why the current code used K directly instead of const K& for key values.

Comment 2

[Graydon Hoare :graydon]

No profile data driving it, no. I'm just beginning to use it to store non-pointer key structures, figured I'd avoid calling all the copy constructors. I imagine it'll run *ok* either way, we're talking 3-5 word key structures, usually. I'd prefer to keep the signatures const & just to avoid thinking about key and value sizes, but can omit that if you feel strongly.

I'm happy to make a specialization of the hasher, at least, for word-sized keys.

Comment 3

[Edwin Smith]

Comment on attachment 394988 [details] [diff] [review]
Brand new shiny bits

I dont feel strongly about const &, at least until we get some evidence of a problem, sounds fine

Comment 4

[Graydon Hoare :graydon]

http://hg.mozilla.org/tracemonkey/rev/82528a81a981

(with partial specialization for pointer keys, restoring the old hash)

Comment 5

[Robert Sayre]

http://hg.mozilla.org/mozilla-central/rev/82528a81a981

Comment 6

[Robert Sayre]

http://hg.mozilla.org/releases/mozilla-1.9.2/rev/e197b445482e