Bug 73154

Summary: String.prototype.toLower should be optimized for 8 bit strings
Product: WebKit Reporter: Michael Saboff <msaboff>
Component: JavaScriptCoreAssignee: Michael Saboff <msaboff>
Status: RESOLVED FIXED    
Severity: Normal CC: darin
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: All   
OS: All   
Attachments:
Description Flags
Patch fpizlo: review+

Description Michael Saboff 2011-11-25 21:16:03 PST 
String.protoype.toLower() uses UString.characters() and should be optimized for the underlying character size.
Comment 1 Michael Saboff 2011-11-25 21:23:46 PST 
Created attachment 116647 [details]
Patch

This speeds up sun spider string-tagcloud by 7%.
Comment 2 Filip Pizlo 2011-11-25 21:36:05 PST 
Comment on attachment 116647 [details]
Patch

Can you put the perf effect in the ChangeLog?
Comment 3 Michael Saboff 2011-11-25 22:17:39 PST 
Committed r101187: <http://trac.webkit.org/changeset/101187>
Comment 4 Darin Adler 2011-11-26 08:30:38 PST 
This removes the optimization for the case where the string was already all lowercase. It seems we could easily retain that by checking if the result of s.impl()->lower() is == s.impl() and if so, returning JSValue::encode(sVal).
Comment 5 Michael Saboff 2011-11-26 09:40:21 PST 
(In reply to comment #4)
> This removes the optimization for the case where the string was already all lowercase. It seems we could easily retain that by checking if the result of s.impl()->lower() is == s.impl() and if so, returning JSValue::encode(sVal).

I had played with this a little and didn't get the return right so it failed some sputnik tests.  I just coded up a correct "already lower case" return and will be posting it in another bug.

It appears that the fast return is worth maybe a little in sun spider performance (.2ms overall).