I have recently upgrade my Ubuntu from 10.10 to 11.04. GCC version is also upgraded from 4.4 to 4.5 automatically. However, some of my heavy math. C codes run slower when compiled with GCC 4.5.
I have tried various optimization flags including "-fexcess-precision=fast". But nothing changes, it runs slower comparing to the executable compiled with GCC 4.4.

By the way, I complied them with GCC 4.4 with "-03 -ffast-math". My machine is IMAC I7. Ubuntu is 64bit.

Any idea?