On Mon, Oct 18, 2010 at 8:27 AM, Nathan Froyd<froydnj@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<edelsohn@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.