On Mon, Oct 18, 2010 at 02:49:21PM +0800, Jie Zhang wrote: > 3. The aforementioned rs6000 hack rs6000_issue_rate was added by > > 2003-03-03 David Edelsohn <edels...@gnu.org> > > * config/rs6000/rs6000.c (rs6000_multipass_dfa_lookahead): Delete. > (TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD): Delete. > (rs6000_variable_issue): Do not return negative value. > (rs6000_issue_rate): Uniformly set issue rate to 1 for first > scheduling pass. > > , which was more than 7 years ago. Is this still needed now?
I asked David about this on IRC several days ago. He indicated that it was necessary to prevent the first scheduling pass from unnecessarily increasing register pressure. I don't know whether anybody has actually tested it with recent GCC, though presumably it did help when it was installed. -Nathan