A question about sched_analyze_insn in sched-deps.c

[Ayal Zaks]

>AFAIK SMS will not do speculative memory access.

Right, SMS does no speculative memory access. Though that might not be
a bad idea...
Ayal.


2011/8/11 Revital Eres <revital.eres@linaro.org>
>
> Hello,
>
> >> I appriciate explanation regarding the following piece of code in
> >> sched_analyze_insn function (sched-deps.c): When handling jump instruction
> >> dependence edges are created between the jump instruction and memory
> >> writes and volatile reads and I'm not quite sure the reason why.
> >
> > Jump instructions can be conditional.  Note the check for whether the
> > next instruction is a barrier.
>
> Thanks for the answer. I'm asking that in the context of SMS --- I'm
> not sure if this dependence is needed when SMS is applied. AFAIK SMS
> will not do speculative memory access.  If that's indeed the case I'll
> submit the following patch.
>
> Thanks,
> Revital
>
> Index: sched-deps.c
> ===================================================================
> --- sched-deps.c        (revision 177556)
> +++ sched-deps.c        (working copy)
> @@ -2777,32 +2777,36 @@ sched_analyze_insn (struct deps_desc *de
>             }
>
>          /* All memory writes and volatile reads must happen before the
> -            jump.  Non-volatile reads must happen before the jump iff
> -            the result is needed by the above register used mask.  */
> +            jump unless the analysis is done for the SMS pass.
> +            Non-volatile reads must happen before the jump iff the
> +            result is needed by the above register used mask.  */
>
> -         pending = deps->pending_write_insns;
> -         pending_mem = deps->pending_write_mems;
> -         while (pending)
> +         if (common_sched_info->sched_pass_id != SCHED_SMS_PASS)
>            {
> -             if (! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
> -               add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
> -             pending = XEXP (pending, 1);
> -             pending_mem = XEXP (pending_mem, 1);
> -           }
> -
> -         pending = deps->pending_read_insns;
> -         pending_mem = deps->pending_read_mems;
> -         while (pending)
> -           {
> -             if (MEM_VOLATILE_P (XEXP (pending_mem, 0))
> -                 && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
> -               add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
> -             pending = XEXP (pending, 1);
> -             pending_mem = XEXP (pending_mem, 1);
> +             pending = deps->pending_write_insns;
> +             pending_mem = deps->pending_write_mems;
> +             while (pending)
> +               {
> +                 if (! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
> +                   add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
> +                 pending = XEXP (pending, 1);
> +                 pending_mem = XEXP (pending_mem, 1);
> +               }
> +
> +             pending = deps->pending_read_insns;
> +             pending_mem = deps->pending_read_mems;
> +             while (pending)
> +               {
> +                 if (MEM_VOLATILE_P (XEXP (pending_mem, 0))
> +                     && ! sched_insns_conditions_mutex_p (insn, XEXP (pending, 0)))
> +                   add_dependence (insn, XEXP (pending, 0), REG_DEP_OUTPUT);
> +                 pending = XEXP (pending, 1);
> +                 pending_mem = XEXP (pending_mem, 1);
> +               }
> +
> +             add_dependence_list (insn, deps->last_pending_memory_flush, 1,
> +                                  REG_DEP_ANTI);
>            }
> -
> -         add_dependence_list (insn, deps->last_pending_memory_flush, 1,
> -                              REG_DEP_ANTI);
>        }
>     }