Bug 16185

Summary: jsRegExpCompile should not add implicit non-capturing bracket
Product: WebKit Reporter: Eric Seidel (no email) <eric>
Component: JavaScriptCoreAssignee: Darin Adler <darin>
Severity: Normal CC: darin, ggaren
Priority: P2    
Version: 523.x (Safari 3)   
Hardware: Mac   
OS: OS X 10.4   
Bug Depends on:    
Bug Blocks: 16186    
Description Flags
patch to omit the outer bracket in cases where it's not needed
patch ggaren: review+

Description Eric Seidel (no email) 2007-11-29 04:07:16 PST
jsRegExpCompile & match should not add implicit non-capturing bracket

Every regexp gets an implicit non-capturing bracket added to the front, and a non-capturing close added to the back of the instruction stream in jsRegExpCompile, match() is then called and expects these.

Removing this trip through the switch() would be a big savings on SunSpider.
Comment 1 Eric Seidel (no email) 2007-11-29 04:08:34 PST
To fix this would likely require breaking out match() into match() and recursive_match() and making sure that only outer match() function is ever called by callers, and that recursive_match() is only ever called from match().

I expect this would fall into the "softball" category of JS speedups.
Comment 2 Darin Adler 2007-12-01 10:40:25 PST
So I misunderstood this bug and added code so that jsRegExpCompile will omit the outer bracket entirely when it's not needed.

This doesn't help the regexp-dna test in SunSpider much at all, because almost all its regular expressions have "|" characters in them, which means they *do* require the outer bracket.

Hence Eric's other suggestion, of optimizing match for this, really turns into a sort of "unrolling" of the match function, which could indeed be helpful for simple regular expressions.

I can't help thinking it's a little bit too specific to this particular test, though. The more I look at the profile the more I realize it's a little bit too biased toward this one particular set of regular expressions.
Comment 3 Darin Adler 2007-12-01 10:41:22 PST
Created attachment 17628 [details]
patch to omit the outer bracket in cases where it's not needed
Comment 4 Darin Adler 2007-12-07 01:29:41 PST
Created attachment 17768 [details]
Comment 5 Geoffrey Garen 2007-12-07 11:38:23 PST
Comment on attachment 17768 [details]

Comment 6 Darin Adler 2007-12-07 12:01:35 PST
Committed revision 28525.