[pklausler]

Language-wise, it's all of F'2018 less coarrays and "LEN" derived type parameters, plus a pile of portable &/or popular language extensions.

[aragilar]

Also, it would be good to know how well it handles older codes of the f77/g77 era (as gfortran is not always well behaved on those).

[pklausler]

Really well, actually. Unless you have a pre-'77 code that requires each DO loop execute at least one iteration, you should be fine.