596140 - reduce size of CSS style rules

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

jseward showed me some data today showing how much memory CSS style rules were taking up.  While there's more we can do to reduce their size, I noticed two very easy wins.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: patch 1: turn mWasMatched into a bit, stealing a bit from mLineNumber

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: patch 2: eliminate all virtual methods from nsCSSRule

nsCSSRule doesn't really need a vtable pointer, and most of its methods didn't need to be virtual in the first place.  The only ones that really did were AddRef and Release, which I just pushed down to derived classes.  That's a slight codesize increase, but one we really ought to find better solutions to...

Comment 3

[Julian Seward [:jseward]]

(as mentioned yesterday to bz) I also have a rudimentary hot-field
profiler, which might help in finding these kinds of opportunities.
I'll see if I can get some results from it today.

Comment 4

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 474991 [details] [diff] [review]
patch 1: turn mWasMatched into a bit, stealing a bit from mLineNumber

I believe MSVC won't pack bitfields of incompatible type.  So you need to make mWaasMatched a PRUint32 as well.

r=me with that.

Comment 5

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 474993 [details] [diff] [review]
patch 2: eliminate all virtual methods from nsCSSRule

r=me.

Comment 6

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

http://hg.mozilla.org/mozilla-central/rev/ebb67011bb43
http://hg.mozilla.org/mozilla-central/rev/d09dcf95a050
http://hg.mozilla.org/mozilla-central/rev/c12c5e990eda

Comment 7

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

The final patch was:
 * the addition of NS_FINAL_CLASS per discussion with bz
 * a missing virtual on ~nsCSSGroupRule that I noticed when doing that