[SOLVED] Optimized compiling with Qt

[soroush]

Hello

How do I apply third level optimization (-O3) for g++ compiler in a Qt project? Setting CXXFLAGS didn't help.

[goetz]

You can try

@

remove possible other optimization flags

QMAKE_CFLAGS_RELEASE -= -O
QMAKE_CFLAGS_RELEASE -= -O1
QMAKE_CFLAGS_RELEASE -= -O2

add the desired -O3 if not present

QMAKE_CFLAGS_RELEASE *= -O3
@

[soroush]

[quote author="Volker" date="1319144953"]You can try

@

remove possible other optimization flags

QMAKE_CFLAGS_RELEASE -= -O
QMAKE_CFLAGS_RELEASE -= -O1
QMAKE_CFLAGS_RELEASE -= -O2

add the desired -O3 if not present

QMAKE_CFLAGS_RELEASE *= -O3
@

[/quote]

Thank you. but didn't worked for C++. I also do this:
@
QMAKE_CXXFLAGS_RELEASE -= -O
QMAKE_CXXFLAGS_RELEASE -= -O1
QMAKE_CXXFLAGS_RELEASE -= -O2

QMAKE_CXXFLAGS_RELEASE *= -O3
@

Is this correct?

Now programs runs a little faster than previous. (should I also re-compile OpenCV and Qt?)

[goetz]

Yes, that's the variable for C++.

Qt itself, and OpenCV are not affected by the change in your project settings, that's right. I'm not sure if you will gain that much speed by switching to -O3. The trolls usually go for sane defaults :) But you will only see if you try.

In case you rebuild Qt, I recommend changing that variable setting in the make spec you use. It's in /path/to/qt/sources/mkspecs

[soroush]

I recompiled Qt and OpenCV with -O3 flags (takes 9 hours) and then recompile my program with -O3 flag too.

I can't believe the results! There was only 8 frames per second with normal configuration.... Now it's 38 frames per second :)
This is my qmake.conf:
@

qmake configuration for linux-g++

Written for GNU/Linux platforms that have both lib and lib64 directories,

like the AMD Opteron.

MAKEFILE_GENERATOR = UNIX
TARGET_PLATFORM = unix
TEMPLATE = app
CONFIG += qt warn_on release incremental link_prl
QT += core gui
QMAKE_INCREMENTAL_STYLE = sublib
QMAKE_CFLAGS -= -O2
QMAKE_CFLAGS -= -O1
QMAKE_CXXFLAGS -= -O2
QMAKE_CXXFLAGS -= -O1
QMAKE_CFLAGS = -m64 -O3
QMAKE_LFLAGS = -m64 -O3
QMAKE_CXXFLAGS = -m64 -O3

include(../common/g++.conf)
include(../common/linux.conf)

QMAKE_LIBDIR_X11 = /usr/X11R6/lib64
QMAKE_LIBDIR_OPENGL = /usr/X11R6/lib64

load(qt_config)
@

God bless gcc ;)