Martin Ettl wrote: > i am playing around with g++-4.3.3 on Ubuntu Linux. The project i am working does a lot of floating point arithmetic (based on double variables). The testplattform i use, is a intel core 2 duo processor. So what optimization flags are good for this plattform? Currently i am using -O3 -funroll-loops, but there are a plenty other. > If you are using the 64-bit compiler, this may be sufficient, but --param max-unrolled-insns=<your choice> or --param max-unroll-times=4 may be useful to make the unrolling less aggressive. I suppose you're not using the 32-bit compiler, where you would set -march=pentium-m or -march=prescott or some other option, to enable partial or full use of sse2. Add -msse3 if you like (either 32- or 64-bit), but you probably have no use for it. -fassociative-math (or, if it doesn't work, -ffast-math) are required for vectorization of sum reductions. Otherwise, they may be undesirable. They are saner in gfortran than in g++. If you use OpenMP, of course you would set -fopenmp.
