qt 5.0 windows x64-msvc2010 very slow

Hello all,

I have successfully ported my application from qt4 to qt5 using the precompiled package from Digia. So the 32bits version runs well and actually runs much faster than my previous, mingw based, version.

Normally I used to donwload pre-compiled packages for 64bits windows from here: http://code.google.com/p/qt-msvc-installer/ but obviously this is not maintained anymore. So I decided to go for it and compile myself qt 5.0.1 (the latest from git) in 64bits-msvc2010. That was not as easy as it seems from the tutos but after all it worked.

The problem is that my qt5_64bits version runs ok but is around 7 times slower than my qt5_32 bits version. I have recompiled qt several times using different options in configure but that didn't change anything. For info my application is very calculation intensive and uses a lot multithread (QConcurrent). Before in Qt4.x I had a huge gain in using a 64bits compilation (msvc2008), and the good thing now is that my qt5_32bits/msvc2010 is almost as fast as my qt4_64bits/msvc2008. But what I don't understand is why my qt5_64bits/msvc2010 is so slow... Probably something wrong in my qt5 compilation but what?

For info my latest (I tried many things) configure options were:

C:\qt5\qt5>configure -debug-and-release -opensource -developer-build -make libs
-make tools -nomake examples -opengl desktop -platform win32-msvc2010 -fully-pro
cess

and qtCreator tells me that the compiler is:

Microsoft Visual C++ Compiler 10.0 (x86)

On linux using precompiled 64 bits packages from Digia the gain is around 15% compared to qt4 version, which is very nice.

Any clue about what I am doing wrong when compiling qt 5.0 in msvc2010/64bits?