Questions about selective scheduler and PowerPC

[Nathan Froyd]

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.

-Nathan