Linux/Compiler Options
Overview
Proper use of compiler options
Don't set a default optimization level for the entire browser build.
Different parts of Mozilla run faster at different optimization levels. For example, cairo, pixman and sqlite are compiled at -O2 because they are fastest at that level while the JS engine is fastest at -Os. [1] If you want to use --enable-optimize, don't add extra optimization flags there. That's a global setting that sets optimization levels throughout the source tree. Instead pass non-optimization flags that you care about via CFLAGS and CXXFLAGS during the build.
Compilers
Notes from dwitte on gcc 4.3 vs. 4.1.2. [2] Also see the original post about possible ways to make gcc 4.1.2 faster as well by using -Os and -finline-limit.
i've tested gcc 4.3 a bit. to summarize, it looks like this pathological -Os behavior is specific to 4.1 branch, and possibly just 4.1.2. also, there are some substantial perf and codesize wins to be had with gcc 4.3. gory details: tested with gcc 4.3 (20080104 pull). "stock configuration" is "-Os -freorder-blocks -fno-reorder-functions". some Tp2 numbers: baseline: gcc 4.3, stock: 142.78 ms stock, with -finline-limit=50: 146.89 ms (+2.9%) -O2: 131.56 ms (-7.9%) for comparison with previous results (comment 0): gcc 4.1.2, stock: 199 ms (+39%) stock, with -finline-limit=50: 149.33 ms (+4.6%) -O2: 142.67 ms (even) |size libxul.so| gcc 4.3, stock: 12,387kb stock, with -finline-limit=50: 12,325kb (-62kb) -O2: 15,061kb (+2,674kb) gcc 4.1.2, stock: 13,249kb (+862kb) stock, with -finline-limit=50: 13,025kb (+638kb) -O2: 15,440kb (+3,053kb) a few points from this data: 1) -Os is very sane on 4.3 by default. 2) on 4.3, relative to -Os, -O2 has improved a lot (8% Tp win, although at a 2.7Mb codesize cost). 3) 4.3 is 5 - 8% faster on Tp2 than 4.1.2, depending on -Os/-O2. 4) 4.3 gives an 400-800k codesize saving over 4.1.2. 3 & 4) are probably the same thing - a result of the hidden visibility propagation improvements introduced in gcc 4.2. these are a major win for us.
Distributions
|
Name |
GCC Version |
Last Build |
|---|---|---|
|
Ubuntu 7.10 |
gcc version 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2) |
2.0.0.11+2nobinonly-0ubuntu0.7.10 (2008-01-07) |
|
gcc flags |
||
|
Fedora 8 |
gcc version 4.1.2 20070925 (Red Hat 4.1.2-33) |
firefox-2.0.0.10-3.fc8 (2008-01-04) |
|
gcc flags |
||
|
CentOS 5.1 |
gcc version 4.1.2 20070626 (Red Hat 4.1.2-14) |
firefox-1.5.0.12-7.el5.centos (2008-01-07) |
|
gcc flags |
||