1050884 - Remove redundant instructions when executing regexps

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Hannes Verschore [:h4writer]]

Some low-hanging fruit that make a difference on execution time in octane-regexp.

Comment 1

[Hannes Verschore [:h4writer]]

Attachment: Remove initializing MatchPairs

Gave me some 50 - 100 points on octane-regexp. The initialization of MatchPairs isn't really necessary since they get init'ed to -1 in the interpreter (for sure) and I'm pretty sure in the jit too. (For safety I added debug code that would trip if this isn't the case)

Comment 2

[Brian Hackett [Laid off!]]

Comment on attachment 8470152 [details] [diff] [review]
Remove initializing MatchPairs

Review of attachment 8470152 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/vm/RegExpObject.cpp
@@ +555,5 @@
> +    for (size_t i = 0; i < pairCount(); i++) {
> +        matches[0].start = -2;
> +        matches[0].limit = -2;
> +    }
> +#endif

I don't think this debug code is necessary, the JIT does initialize its saved registers (NativeRegExpMacroAssembler.cpp:250), but maybe add a comment above the allocOrExpand call saying that the RegExp engine fills in all the registers on a match.

Comment 3

[Hannes Verschore [:h4writer]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/8b35df13bf69

Comment 4

[Hannes Verschore [:h4writer]]

Fix build failures.
https://hg.mozilla.org/integration/mozilla-inbound/rev/0d22e48a9501

(Note this doesn't make a big difference on awfy, but locally this still gives this 50-100 point increase.)

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/8b35df13bf69
https://hg.mozilla.org/mozilla-central/rev/0d22e48a9501