GNAT uses the gcc back end, all the specialized
gcc optimization switches are potentially usable. These switches
have not been extensively tested with GNAT but can generally be expected
to work. Examples of switches in this category are
the various target-specific -m options (in particular, it has been
observed that -march=pentium4 can significantly improve performance
on appropriate machines). For full details of these switches, see
Hardware Models and Configurations.