Find out GCC optimizations of -march -mtune etc

If you want to check what optimizations your current gcc settings give you, you need to use:

echo | gcc -dM -E - -march=native

You can then grep the output to check stuff like MMX, SSE or 3dNOW.

To test a specific setting, like “-march=x86-64 -msse3” :

echo | gcc -dM -E - -march=x86-64 -msse3

To see what gcc recommends for your platform:

echo | gcc -dM -E - -march=native