[patch][Ping #3] PR80929: Realistic PARALLEL cost in seq_cost.

[Georg-Johann Lay]

On 28.06.2017 22:18, Wilco Dijkstra wrote:
> Georg-Johann Lay wrote:
> 
> @@ -5300,6 +5300,9 @@ seq_cost (const rtx_insn *seq, bool spee
>         set = single_set (seq);
>         if (set)
>           cost += set_rtx_cost (set, speed);
> +      else if (INSN_P (seq)
> +	       && PARALLEL == GET_CODE (PATTERN (seq)))
> +	cost += insn_rtx_cost (PATTERN (seq), speed);
>         else
>           cost++;
> 
> insn_rtx_cost may return zero if it can't find something useful in the parallel,
> which means it may return a lower cost and even zero. Not sure whether this
> is important, but in eg. combine a cost of zero means infinite and so could have
> unintended consequences. So incrementing cost with a non-zero value
> if insn_rtx_cost == 0 would seem safer.

Updated patch below, it just adds 1 (which is 1/4 of CONST_N_INSNS) to
avoid zero.


> Also why does the else do cost++ and not cost += COSTS_N_INSNS (1)?
> 
> Wilco

Dunno, I didn't change this.  Maybe it's also just to escape 0.

Johann

gcc/
     PR middle-end/80929
     * rtlanal.c (seq_cost) [PARALLEL]: Get cost from insn_rtx_cost
     instead of assuming cost of 1.


Index: rtlanal.c
===================================================================
--- rtlanal.c	(revision 248745)
+++ rtlanal.c	(working copy)
@@ -5300,6 +5300,9 @@ seq_cost (const rtx_insn *seq, bool spee
        set = single_set (seq);
        if (set)
          cost += set_rtx_cost (set, speed);
+      else if (INSN_P (seq)
+	       && PARALLEL == GET_CODE (PATTERN (seq)))
+	cost += 1 + insn_rtx_cost (PATTERN (seq), speed);
        else
          cost++;
      }