1417048 - Firefox code build options for Windows are not set correctly.

Status: RESOLVED DUPLICATE of bug 1830453

(Firefox Build System :: General, defect)

Description

[Elle Solomina (she/her)]

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:56.0) Gecko/20100101 Firefox/56.0
Build ID: 20171024165158

Steps to reproduce:

After I opened the page
about:buildconfig
I saw the problem: Firefox code build options for Windows are not set correctly.


z:/build/build/src/vs2015u3/VC/bin/amd64_x86/cl.exe 19.00.24213 -utf-8 -TP -nologo -wd5026 -wd5027 -Zc:sizedDealloc- -wd4091 -wd4577 -D_HAS_EXCEPTIONS=0 -W3 -Gy -Zc:inline -arch:SSE2 -Gw -wd4251 -wd4244 -wd4267 -wd4800 -wd4595 -we4553 -GR- -Zi -GL -wd4624 -wd4952 -O1 -Oi -Oy-

it's FAIL: 

These option: -O1 — are incorrect for release if you use MSVC, should be -O2.

The page for the assembly manual 
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Build_Instructions/Configuring_Build_Options
 also talks about it.

ac_add_options --enable-optimize 

    Enables the default compiler optimization options

    Note: This is enabled by default

ac_add_options --enable-optimize=-O2 
    Chooses particular compiler optimization options. In most cases, this will not give the desired results, unless you know the Mozilla codebase very well; note, however, that if you are building with the Microsoft compilers, you probably do want this as -O1 will optimize for size, unlike GCC.


Actual results:

You use -O1 in MSVC instead of -O2


Expected results:

The essence of the problem: people complain that Firefox is very slow, and you do not even use the standard optimizations for the release. Really?! Please use -O2 (or -Ox) optimization for Windows builds!

Comment 1

[(not currently active) Ted Mielczarek]

Hello, thanks for your concern, but it's unwarranted. We have spent quite a bit of time over the years choosing optimal compiler settings for Firefox, and rest assured that larger numbers are not always better. Optimizing for size vs. speed is a tradeoff, and larger code size often makes a program slower in many scenarios.

In any event, since Firefox 3 we have shipped our Windows builds with MSVC's Profile-Guided Optimization, which applies targeted optimization to hot code paths:
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Build_Instructions/Building_with_Profile-Guided_Optimization

If you have data to suggest that changing our optimization flags results in real-world performance improvements when Firefox is built with PGO we would love to see it!

Comment 2

[Elle Solomina (she/her)]

Thank you for your reply. If you use PGO then everything is fine.