Bug 85258 – Early-out for subtracting a non-intersecting region

• Status: RESOLVED
• Resolution: FIXED
• Component: New Bugs

[Dana Jansens]

Early-out for subtracting a non-intersecting region

[Dana Jansens]

Created attachment 139578 [details]
Patch

[Hajime Morrita]

Comment on attachment 139578 [details]
Patch

Harvest all low hanging fruits!!

[WebKit Review Bot]

Comment on attachment 139578 [details]
Patch

Clearing flags on attachment: 139578

Committed r115716: <http://trac.webkit.org/changeset/115716>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.

[Darin Adler]

Is this change for better performance or is it related to correctness? If it’s for better performance, what test demonstrates the improvement? How good is the improvement?

[Dana Jansens]

It is for performance, if you subtract a Region that does not intersect, you would make a memcpy of the orignal region. Region copies are showing themselves to be very costly, you can see some backstory here https://bugs.webkit.org/show_bug.cgi?id=81076

I must confess I'm not sure what you mean by a test though, we use unit tests and layout tests to verify correctness, but I've never been asked to write a test to show performance differences.

[Darin Adler]

Most performance-driven changes include information about some kind of performance test and data about the results before and after the code change. I can find you examples if you haven’t seen that in the WebKit project before.

[Dana Jansens]

Sure, I'd love a good example, thanks.

[Darin Adler]

I’m not sure these are the best examples, but three I found with a quick search are these:

http://trac.webkit.org/changeset/114912
http://trac.webkit.org/changeset/114351
http://trac.webkit.org/changeset/112387