> Not the OP, but: -march says the compiler can assume that the features of that particular CPU architecture family, which is broken out by generation, can be relied upon. In the worst case the compiler could in theory generate code that does not run on older CPUs of the same family or from different vendors.

Or on newer CPUs of the same vendor (e.g. AMD dropped some instructions in Zen that Intel didn't pick up) or even in different CPUs of the same generation (Intel market segmenting shenanigans with AVX512).