GCC changed their
-marchoptions in the recently-released version 4.9. GCC 4.8, which notably shipped in Ubuntu 14.04 (Trusty Tahr), used some inscrutable aliases; the equivalent to 4.9's
corei7-avxfor instance. Here's a table of the subset that's most interesting to me:
|GCC 4.8||GCC 4.9|
Broadwell and Westmere are not explicitly supported in the older release. Based on its definition in the gcc-4.9 sources, I believe the equivalent set of flags for Westmere in gcc 4.8 would be
-march=corei7 -maes -mpclmul. And naturally, the
corei7-avx2option for Haswell would be the best for targeting Broadwell.