Hi! I tried to build optimize and debug version of MPICH 3.0 rc1 and noticed some problems with compiler optimization flags. Looks like -O2 is set implicitly. For optimize configuration command like contains -O2 and -O3: ./configure --prefix=${InstallDir} \ --with-pm=hydra --with-device=ch3:nemesis \ --disable-chekpointing \ --enable-strict --enable-fast=O3 \ --disable-f77 --disable-fc \ CC=${GCCDir}/bin/gcc CFLAGS="-m32 -fPIC" \ CPP=${GCCDir}/bin/cpp \ CXX=${GCCDir}/bin/g++ CXXFLAGS="-m32 -fPIC" \ CXXCPP=${GCCDir}/bin/cpp For debug one -O2, but optimization is disabled: ./configure --prefix=${InstallDir} \ --with-pm=hydra --with-device=ch3:nemesis \ --disable-chekpointing \ --enable-strict --disable-fast -enable-g=debug \ --disable-f77 --disable-fc \ CC=${GCCDir}/bin/gcc CFLAGS="-m32 -fPIC" \ CPP=${GCCDir}/bin/cpp \ CXX=${GCCDir}/bin/g++ CXXFLAGS="-m32 -fPIC" \ CXXCPP=${GCCDir}/bin/cpp Eugene.