On Tue, Sep 22, 2009 at 11:50 PM, Vladimir Makarov <vmaka...@redhat.com> wrote: > Ian Lance Taylor wrote: >> >> "Amker.Cheng" <amker.ch...@gmail.com> writes: >> >> >>> >>> In function new_ready, it calls to min_insn_conflict_delay with >>> "min_insn_conflict_delay (curr_state, next, next)". >>> But the function's comments say that it returns minimal delay of issue of >>> the 2nd insn after issuing the 1st in given state. >>> Why the last two parameter for the call are both "next"? >>> seems conflict with the comments. >>> >> >> > > Amker, thanks for finding this issue. It's great pleasure if can help anything.
>> >> This change dates back to the first DFA scheduler patch. It does seem a >> little odd, particularly as the call in new_ready is the only use of >> min_insn_conflict_delay. CC'ing vmakarov in case he remembers anything >> about this old code. >> > > I've not remembered this. I guess it was a result of long period of > transition from the old pipeline hazard recognizier to the DFA one which > required to rewrite all old pipeline descriptions. > > Also after starring at this code for some time, I don't like this code. > Now I'd use min_issue_delay (curr_state, next) which is delay of issuing > next in the current function unit reservation state instead of > min_insn_conflict_delay (curr_state, next, next) which is a delay of > issuing the first insn (next) after issuing the second insn (next) on a free > processor (when all function units are free). Probably it was a typo. > Although I think that such change (in many other conditions to move insn > speculatively to the ready list) will not give a visible improvement for > most processors, I'll try it. > > It looks to me that probably I had also some plans for usage of > min_insn_conflict_delay, but I forgot them because it was long ago. > > Is it the delay of issuing next in the current reservation state which expected here? seems the call to min_insn_conflict_delay does nothing harm, except may result in more or less speculative motions(which are all valid ones). -- Best Regards.
