Re: c/3917: IA-64 assembler output shows erroneous cycle counting

[wilson at gcc dot gnu dot org]

Synopsis: IA-64 assembler output shows erroneous cycle counting

State-Changed-From-To: analyzed->closed
State-Changed-By: wilson
State-Changed-When: Thu Sep 20 16:56:14 2001
State-Changed-Why:
    I looked at the issue of making better choices about
    putting padding nops into partially full bundles.  The
    info we need to make a better choice is not easily
    available at the place where we need to make the choice.
    I tried adding a quick hack to pad with a nop if a bundle
    has the first two slots full, and the split point was
    after the third slot.  I would expect this to show some
    performancce improvement, but not as much as we could do
    if we had better info available.
    Index: ia64.c
    ===================================================================
    RCS file: /cvs/gcc/gcc/gcc/config/ia64/ia64.c,v
    retrieving revision 1.120
    diff -p -r1.120 ia64.c
    *** ia64.c	2001/08/23 19:27:54	1.120
    --- ia64.c	2001/09/19 18:44:24
    *************** cycle_end_fill_slots (dump)
    *** 5508,5513 ****
    --- 5523,5537 ----
            slot++;
          }
      #endif
    + 
    +   if ((slot == 2 && sched_data.split >= 3)
    +       || (slot == 5 && sched_data.split == 6))
    +     {
    +       sched_data.types[slot] = packet->t[slot];
    +       sched_data.insns[slot] = 0;
    +       sched_data.stopbit[slot] = 0;
    +       slot++;
    +     }
      
        sched_data.first_slot = sched_data.cur = slot;
      }
    
    I tried running spec95 int and fp benchmarks, with no
    patch, the first patch, and both patches.  I also added
    a hack to disable Jan Hubicka's July 15 loop.c patch,
    which is causing performance regressions.  I get no
    observable performancec increase from the first patch,
    and I get a small performance decrease from the second
    patch.  From this I conclure that my first patch is
    desirable, but my second one is not, and that no further
    investigation is worthwhile at the moment for this
    problem.
    
    We will still have the problem that the scheduler will
    occasionally put two FP insns in different cycles when
    they could go in the same cycle, but in most cases the
    scheduler should now get this right, and I see no
    performance increase from trying to fix the remaining
    cases.
    
    I will be checking in my first patch.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=3917&database=gcc