Re: Make max_issue honor issue_rate

[Jie Zhang <jie at codesourcery dot com>]

On 10/26/2010 05:58 AM, Maxim Kuvyrkov wrote:
> On 10/25/10 2:36 PM, Jie Zhang wrote:
>
> > 4 units: a, b, c, d.
> >
> > insn 1 uses a, insn 2 uses b, insn 3 uses c, insn 4 uses d.
> >
> > and we set issue_rate to 3. In this case, we can only issue insn 1, 2, 3
> > but not 4 although its unit is free.
> >
> > To extend this example a little, i.e. insn4 uses nothing, (it does not
> > change the state, right? I'm not very sure), it still can not be issued.
> >
> > So I think we should use "top - choice_stack >= more_issue" instead of
> > "top->n >= more_issue". Am I right?
>
> I think the 'n' field was introduced for a reason. DFA description has
> the "nothing" reservation that specifies that a particular instruction
> does not have a noticeable effect on a CPU (imagine a nop instruction
> that gets optimized out by decoder and does not get into the pipeline).
OK. This version of the patch removes some unnecessary changes in your 
version to ease the scheduler maintainer review.

--
Jie Zhang
CodeSourcery

	* haifa-sched.c (ISSUE_POINTS): Remove.
	(max_issue): Don't issue more than issue_rate instructions.

Index: haifa-sched.c
===================================================================
--- haifa-sched.c	(revision 165970)
+++ haifa-sched.c	(working copy)
@@ -199,10 +199,6 @@ struct common_sched_info_def *common_sch
 /* The minimal value of the INSN_TICK of an instruction.  */
 #define MIN_TICK (-max_insn_queue_index)
 
-/* Issue points are used to distinguish between instructions in max_issue ().
-   For now, all instructions are equally good.  */
-#define ISSUE_POINTS(INSN) 1
-
 /* List of important notes we must keep around.  This is a pointer to the
    last element in the list.  */
 rtx note_list;
@@ -2444,8 +2440,7 @@ static int cached_issue_rate = 0;
    insns is insns with the best rank (the first insn in READY).  To
    make this function tries different samples of ready insns.  READY
    is current queue `ready'.  Global array READY_TRY reflects what
-   insns are already issued in this try.  MAX_POINTS is the sum of points
-   of all instructions in READY.  The function stops immediately,
+   insns are already issued in this try.  The function stops immediately,
    if it reached the such a solution, that all instruction can be issued.
    INDEX will contain index of the best insn in READY.  The following
    function is used only for first cycle multipass scheduling.
@@ -2458,7 +2453,7 @@ int
 max_issue (struct ready_list *ready, int privileged_n, state_t state,
 	   int *index)
 {
-  int n, i, all, n_ready, best, delay, tries_num, max_points;
+  int n, i, all, n_ready, best, delay, tries_num;
   int more_issue;
   struct choice_entry *top;
   rtx insn;
@@ -2477,19 +2472,9 @@ max_issue (struct ready_list *ready, int
     }
 
   /* Init max_points.  */
-  max_points = 0;
   more_issue = issue_rate - cycle_issued_insns;
   gcc_assert (more_issue >= 0);
 
-  for (i = 0; i < n_ready; i++)
-    if (!ready_try [i])
-      {
-	if (more_issue-- > 0)
-	  max_points += ISSUE_POINTS (ready_element (ready, i));
-	else
-	  break;
-      }
-
   /* The number of the issued insns in the best solution.  */
   best = 0;
 
@@ -2513,12 +2498,17 @@ max_issue (struct ready_list *ready, int
       if (/* If we've reached a dead end or searched enough of what we have
 	     been asked...  */
 	  top->rest == 0
-	  /* Or have nothing else to try.  */
-	  || i >= n_ready)
+	  /* or have nothing else to try...  */
+	  || i >= n_ready
+	  /* or should not issue more.  */
+	  || top->n >= more_issue)
 	{
 	  /* ??? (... || i == n_ready).  */
 	  gcc_assert (i <= n_ready);
 
+	  /* We should not issue more than issue_rate instructions.  */
+	  gcc_assert (top->n <= more_issue);
+
 	  if (top == choice_stack)
 	    break;
 
@@ -2541,7 +2531,7 @@ max_issue (struct ready_list *ready, int
 		  /* This is the index of the insn issued first in this
 		     solution.  */
 		  *index = choice_stack [1].index;
-		  if (top->n == max_points || best == all)
+		  if (top->n == more_issue || best == all)
 		    break;
 		}
 	    }
@@ -2574,7 +2564,7 @@ max_issue (struct ready_list *ready, int
 
 	      n = top->n;
 	      if (memcmp (top->state, state, dfa_state_size) != 0)
-		n += ISSUE_POINTS (insn);
+		n++;
 
 	      /* Advance to the next choice_entry.  */
 	      top++;