In nsRegionWin::SetTo we destroy the old region and creates a new one. It would be faster to just set the existing region to a new position with SetRectRgn. That would save us a DeleteObject and I bet SetRectRgn is much faster than the CreateRectRgn we use right now and also it would save a couple of byte of code size. Right now nsRegionWin::SetTo is 7% of the problematic DHTML page in bug 124178 but that extremely high percentage is probably just because it's called too often. I think.

Here is a patch. I fixed Init to also don't delete/create when it can as well just set the region. Reviews? Kevin?

A SetRectRgn is ~2us. A CreateRectRgn was ~6us.

Comment on attachment 68772 [details] [diff] [review] Replace DeleteObject/CreateRectRgn with SetRectRgn r=kmcclusk@netscape.com.

Rod can you take a look at Daniel's patch?

Comment on attachment 68772 [details] [diff] [review] Replace DeleteObject/CreateRectRgn with SetRectRgn sr=attinasi. Please indicate how this was tested - I am assuming it was tested :)

I've been running with it for a week now and I'm still alive. :-) I've also stepped through the code and the same things happens now as before. Taking for checkin.

Fix checked in.