gcc generic march for all the x64 platforms

Question

GCC have -march= and -mtune option as described here. But it is not obvious which of the options to choose for x64 platform as generic

Answer 1

The generic x86-64 -march is -march=x86-64.

It is usually the default for GCC targeting x86-64, but that default can be changed at configure time by passing appropriate value to --with-arch.