1440072 - Eliminate unused cases for XPTConstValue

Status: RESOLVED FIXED

(Core :: XPCOM, enhancement)

Description

[Andrew McCreight [:mccr8]]

XPTConstValue is a union that can hold integers of various sizes (8, 16, 32, 64), but it turns out that xpt.py will only ever generate {u,}int{16,32} constants (as seen in the variable typemap in class Constant). Eliminating the unused cases reduces the code complexity a bit, and reduces the size of XPTConstValue from 64 bits to 32 bits.

This reduces xpti-working-set from 0.87 MB to 0.85 MB in about:memory on Linux64.

xptiInterfaceEntry::GetConstant(), which seems to be the only thing that reads things out of these tags, doesn't even implement any of these cases, aside from int8 and uint8, so the other cases could never have worked in any real way.

Comment 1

[Andrew McCreight [:mccr8]]

Attachment: Bug 1440072 - Eliminate unused cases for XPTConstValue.

xpt.py only generates constants for a couple of the cases that
XPTConstValue supports. Eliminating the unused cases reduces the size
of this data structure from 64-bit to 32-bit, which reduces the memory
usage of xpti-working set by about 0.02MB.

Review commit: https://reviewboard.mozilla.org/r/222090/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/222090/

Comment 2

[Nicholas Nethercote [inactive]]

Comment on attachment 8952858 [details]
Bug 1440072 - Eliminate unused cases for XPTConstValue.

https://reviewboard.mozilla.org/r/222090/#review228012

I wonder about keeping the i8 and u8 cases -- it's the 64-bit case removals that save memory, right? But if i8/u8 are not used and not fully implemented, I guess it's not worth it.

Comment 3

[Andrew McCreight [:mccr8]]

It should be easy enough to add them back if anybody wants them.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/cb9d2116b32d
Eliminate unused cases for XPTConstValue. r=njn

Comment 5

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/cb9d2116b32d