The g77 command supports all the options supported by the gcc command. See GCC Command Options (Using the GNU Compiler Collection (GCC)), for information on the non-Fortran-specific aspects of the gcc command (and, therefore, the g77 command).
All gcc and g77 options are accepted both by g77 and by gcc (as well as any other drivers built at the same time, such as g++), since adding g77 to the gcc distribution enables acceptance of g77 options by all of the relevant drivers.
In some cases, options have positive and negative forms; the negative form of -ffoo would be -fno-foo. This manual documents only one of these two forms, whichever one is not the default.