On Mon, Oct 18, 2010 at 8:27 AM, Nathan Froyd <froy...@codesourcery.com> wrote: > 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.
I am not sure when it last was re-checked, but it was checked after sched_pressure was added. When that option is not enabled, the issue_rate change still helped. - David
