Comment by zahllos

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.

-mtune says "generate code that is optimised for this architecture" but it doesn't trigger arch specific features.

Whether these are right or not depends on what you are doing. If you are building gentoo on your laptop you should absolutely -mtune=native and -march=native. That's the whole point: you get the most optimised code you can for your hardware.

If you are shipping code for a wide variety of architectures and crucially the method of shipping is binary form then you want to think more about what you might want to support. You could do either: if you're shipping standard software pick a reasonable baseline (check what your distribution uses in its cflags). If however you're shipping compute-intensive software perhaps you load a shared object per CPU family or build your engine in place for best performance. The Intel compiler quite famously optimised per family, included all the copies in the output and selected the worst one on AMD ;) (https://medium.com/codex/fixing-intel-compilers-unfair-cpu-d...)