Monday, February 18, 2008

GCC slowness... problem solved

[Ed: Milan solved the speed problem for g++, here is what he wrote on devel-list]
Hi all,

Today I tried building FlameRobin with MSVC Express. It works really
nice and it builds FR from scratch in about 2.5 minutes on this
machine where I tried it (Intel Celeron M 1.4GHz with 256MB RAM). This
in on Windows XP Pro with all anti-virus and similar software turned

Then I tried on Linux (it's a dual boot machine) and GCC took 272
seconds, i.e. 4.5 minutes. Both compilers are using PCH. I got really
frustrated about this in the past, so much that I considered to
install Windows on my machine and do FR development there.

But, I suddenly got the idea that GCC might be losing too much time
optimizing. So, I tried to lover the optimization from level 2 to
level 1. I got slight improvement: 225 seconds. Still too slow. Then I
turned it off, and I got the amazing 130 seconds, i.e. 2:10. This is
quite acceptable to development and I guess I'll only use -O2 when we
build the release versions from now on.

The option can be changed by setting CXXFLAGS environment variable
before you run 'configure' script. Something like this (if your shell
is bash):

$ export CXXFLAGS=
$ ../configure ...
$ make

It looks like GCC isn't that bad after all.

Milan Babuskov

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