I have built an up-to-date vanilla GCC from svn with these flags:
../configure \
--enable-languages=c,c++ \
--disable-nls \
--enable-multilib \
--prefix=/opt/other/gcc-svn \
--program-suffix=-svn \
--with-system-zlib
First with clang 3.4, then I thought it may be clang's fault (with a grain of salt) and rebuilt GCC once
more with GCC 4.8.1, which led to the exact same result.
The resulting GCC is about 17 seconds slower than GCC 4.8.1 when I try to compile a C++ project with approx. 150k lines of code.
These are the build times I get (-O3):
g++ 4.9: 48 seconds g++ 4.8: 31 seconds clang 3.4: 13 secondsDid I miss a configure flag or is GCC 4.9 really that much slower?!
If the compiler is slower than expected, passing the -ftime-report flag can help figuring out what's going on.
Luckily, it also helped in this case: With -ftime-report GCC printed
'Extra diagnostic checks enabled; compiler may run slowly. Configure with --enable-checking=release to disable checks.'
Thomas has rebuilt the compiler from source accordingly and the problem is gone!