108597 - shrink nsStr

Status: RESOLVED FIXED

(Core :: XPCOM, defect, P1)

Description

[Alec Flett]

Man! Has anyone noticed that:
1) nsStr counts for 10M out of 25M in the bloat logs
2) nsStr is 20 bytes long
3) 8 bytes of nsStr are used for two booleans (mCharSize and mOwnsBuffer)

With a simple 10-15 line change, I can shrink nsStr to 16 bytes, by making
mCharSize a PRInt8 and making mOwnsBuffer a PRPackedBool, both 8 bytes. Rounded
up to the nearest 4 bytes, these two variables still take 4 bytes, but it will
save about 2 Megs in the bloat logs on tinderbox.

I'm going to work on further reductions to roll these two boolean variables into
the high bytes of mLength and mCapacity, reducing this object to a mere 8 bytes,
but I'd like to get this short patch into 0.9.6 right now.

Comment 1

[Alec Flett]

oops, assign to myself, I have the fix

Comment 2

[Alec Flett]

Attachment: shrink nsStr by 4 bytes

Comment 3

[Alec Flett]

I totally mucked up indentation in nsStr.h, but I'll fix that before landing.

Comment 4

[Alec Flett]

cc'ing waterson for an sr=

Comment 5

[Chris Waterson]

sr=waterson

Comment 6

[jag (Peter Annema)]

Comment on attachment 56622 [details] [diff] [review]
shrink nsStr by 4 bytes

Sure, low fruit. r=jag

Comment 7

[Alec Flett]

in my tree, I also moved mCharSize and mOwnsBuffer after mStr/mUStr to make sure
mStr/mUStr stay aligned (dumb compilers might not)

Comment 8

[Alec Flett]

thanks guys, fixed!