244475 - string optimization in HTMLContentSink::AddAttributes

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Brian Ryner (not reading)]

Because of the way shared string buffers work, HTMLContentSink::AddAttributes
isn't quite optimal in the way it does an atom lookup for attribute names.  In
particular, calling ToLowerCase on the shared buffer heap-allocates a new
(mutable) buffer, then lowercases the string in-place, then the string is copied
again (while being converted to UTF-8) into a stack buffer when do_GetAtom is
called.  In addition to this, dealing with the shared buffer incurs overhead
from doing an atomic increment on the buffer reference count (which is silly
since we know we'll need a mutable buffer).

I have a patch which does the UTF-8 conversion (into a mutable buffer) up-front,
which gets rid of the heap allocation, extra string copy, and atomic increment
overhead.  It seems to give a Tp win of about 1%.

Comment 1

[Brian Ryner (not reading)]

Attachment: patch

Comment 2

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 149181 [details] [diff] [review]
patch

r+sr=bzbarsky; fix nsHTMLFragmentContentSink too, though?

Comment 3

[Brian Ryner (not reading)]

checked in.