Bug 20333 – improve JavaScript speed when handling single-character strings

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Darin Adler]

We think this will work!

[Darin Adler]

Created attachment 22708 [details]
some early work in progress

[Darin Adler]

Created attachment 22766 [details]
eliminate JSValue::type()

[Geoffrey Garen]

Comment on attachment 22766 [details]
eliminate JSValue::type()

r=me

Please try not to conflict with bug 20389.

It looks like you re-autogenerated a bunch of SVG tests, too. Was that intentional?

+        if (v1 == JSImmediate::from(0))
+            return !JSImmediate::isImmediate(v2)
+                && static_cast<JSCell*>(v2)->isNumber()
+                && static_cast<JSNumberCell*>(v2)->value() == 0;
+        return v2 == JSImmediate::from(0)
+            && !JSImmediate::isImmediate(v1)
+            && static_cast<JSCell*>(v1)->isNumber()
+            && static_cast<JSNumberCell*>(v1)->value() == 0;

This surprised me a little bit. Is there a case where 0 gets stored on the heap instead of as an immediate? How do we know this doesn't happen with other numbers?

[Darin Adler]

(In reply to comment #3)
> It looks like you re-autogenerated a bunch of SVG tests, too. Was that
> intentional?

No. That was an accident and I didn't notice it when creating the patch.

> +        if (v1 == JSImmediate::from(0))
> +            return !JSImmediate::isImmediate(v2)
> +                && static_cast<JSCell*>(v2)->isNumber()
> +                && static_cast<JSNumberCell*>(v2)->value() == 0;
> +        return v2 == JSImmediate::from(0)
> +            && !JSImmediate::isImmediate(v1)
> +            && static_cast<JSCell*>(v1)->isNumber()
> +            && static_cast<JSNumberCell*>(v1)->value() == 0;
> 
> This surprised me a little bit. Is there a case where 0 gets stored on the heap
> instead of as an immediate? How do we know this doesn't happen with other
> numbers?

This is to handle negative 0.

[Darin Adler]

Comment on attachment 22766 [details]
eliminate JSValue::type()

Clearing review flag since this patch was landed and the bug is not yet fixed.

[Darin Adler]

Created attachment 22926 [details]
remove the need for InternalFunction to return a UString& to its name

Geoff, this is what we talked about.

[Cameron Zwarich (cpst)]

Comment on attachment 22926 [details]
remove the need for InternalFunction to return a UString& to its name

I don't think you want to commit the first change to the XCode project, because Geoff committed changes to all of the XCode projects to update them to XCode 3.1 and that undoes one of them. However, I am no XCode wizard, so I may be wrong.

Otherwise r=me.

[Darin Adler]

Comment on attachment 22926 [details]
remove the need for InternalFunction to return a UString& to its name

I've decided not to make this change at this time. I'm taking a different approach to optimizing the single character case.

[Darin Adler]

Created attachment 23077 [details]
work in progress

[Darin Adler]

Created attachment 23083 [details]
patch

[Maciej Stachowiak]

r=me

Consider breaking SmallStringStorage into its own header and implementation file.

[Darin Adler]

http://trac.webkit.org/projects/webkit/changeset/36006