[PATCH] IBM zSystems: Do not propagate scheduler state across basic blocks [PR108102]

[PATCH] IBM zSystems: Do not propagate scheduler state across basic blocks [PR108102]

[Stefan Schulze Frielinghaus]

So far we propagate scheduler state across basic blocks within EBBs and
reset the state otherwise.  In certain circumstances the entry block of
an EBB might be empty, i.e., no_real_insns_p is true.  In those cases
scheduler state is not reset and subsequently wrong state is propagated
to following blocks of the same EBB.

Since the performance benefit of tracking state across basic blocks is
questionable on modern hardware, simply reset the state for each basic
block.

Fix also resetting f{p,x}d_longrunning.

Bootstrapped and regtested on IBM zSystems.  Ok for mainline?

gcc/ChangeLog:

	* config/s390/s390.cc (s390_bb_fallthru_entry_likely): Remove.
	(struct s390_sched_state): Initialise to zero.
	(s390_sched_variable_issue): For better debuggability also emit
	the current side.
	(s390_sched_init): Unconditionally reset scheduler state.
---
 gcc/config/s390/s390.cc | 42 +++++++----------------------------------
 1 file changed, 7 insertions(+), 35 deletions(-)

diff --git a/gcc/config/s390/s390.cc b/gcc/config/s390/s390.cc
index a9bb610385b..9317f33e9c9 100644
--- a/gcc/config/s390/s390.cc
+++ b/gcc/config/s390/s390.cc
@@ -14872,29 +14872,6 @@ s390_z10_prevent_earlyload_conflicts (rtx_insn **ready, int *nready_p)
   ready[0] = tmp;
 }
 
-/* Returns TRUE if BB is entered via a fallthru edge and all other
-   incoming edges are less than likely.  */
-static bool
-s390_bb_fallthru_entry_likely (basic_block bb)
-{
-  edge e, fallthru_edge;
-  edge_iterator ei;
-
-  if (!bb)
-    return false;
-
-  fallthru_edge = find_fallthru_edge (bb->preds);
-  if (!fallthru_edge)
-    return false;
-
-  FOR_EACH_EDGE (e, ei, bb->preds)
-    if (e != fallthru_edge
-	&& e->probability >= profile_probability::likely ())
-      return false;
-
-  return true;
-}
-
 struct s390_sched_state
 {
   /* Number of insns in the group.  */
@@ -14905,7 +14882,7 @@ struct s390_sched_state
   bool group_of_two;
 } s390_sched_state;
 
-static struct s390_sched_state sched_state = {0, 1, false};
+static struct s390_sched_state sched_state;
 
 #define S390_SCHED_ATTR_MASK_CRACKED    0x1
 #define S390_SCHED_ATTR_MASK_EXPANDED   0x2
@@ -15405,7 +15382,7 @@ s390_sched_variable_issue (FILE *file, int verbose, rtx_insn *insn, int more)
 
 	      s390_get_unit_mask (insn, &units);
 
-	      fprintf (file, ";;\t\tBACKEND: units on this side unused for: ");
+	      fprintf (file, ";;\t\tBACKEND: units on this side (%d) unused for: ", sched_state.side);
 	      for (j = 0; j < units; j++)
 		fprintf (file, "%d:%d ", j,
 		    last_scheduled_unit_distance[j][sched_state.side]);
@@ -15443,17 +15420,12 @@ s390_sched_init (FILE *file ATTRIBUTE_UNUSED,
      current_sched_info->prev_head is the insn before the first insn of the
      block of insns to be scheduled.
      */
-  rtx_insn *insn = current_sched_info->prev_head
-    ? NEXT_INSN (current_sched_info->prev_head) : NULL;
-  basic_block bb = insn ? BLOCK_FOR_INSN (insn) : NULL;
-  if (s390_tune < PROCESSOR_2964_Z13 || !s390_bb_fallthru_entry_likely (bb))
-    {
-      last_scheduled_insn = NULL;
-      memset (last_scheduled_unit_distance, 0,
+  last_scheduled_insn = NULL;
+  memset (last_scheduled_unit_distance, 0,
 	  MAX_SCHED_UNITS * NUM_SIDES * sizeof (int));
-      sched_state.group_state = 0;
-      sched_state.group_of_two = false;
-    }
+  memset (fpd_longrunning, 0, NUM_SIDES * sizeof (int));
+  memset (fxd_longrunning, 0, NUM_SIDES * sizeof (int));
+  sched_state = {};
 }
 
 /* This target hook implementation for TARGET_LOOP_UNROLL_ADJUST calculates
-- 
2.39.1

Re: [PATCH] IBM zSystems: Do not propagate scheduler state across basic blocks [PR108102]

[Andreas Krebbel]

On 2/11/23 16:59, Stefan Schulze Frielinghaus wrote:
> So far we propagate scheduler state across basic blocks within EBBs and
> reset the state otherwise.  In certain circumstances the entry block of
> an EBB might be empty, i.e., no_real_insns_p is true.  In those cases
> scheduler state is not reset and subsequently wrong state is propagated
> to following blocks of the same EBB.
> 
> Since the performance benefit of tracking state across basic blocks is
> questionable on modern hardware, simply reset the state for each basic
> block.
> 
> Fix also resetting f{p,x}d_longrunning.
> 
> Bootstrapped and regtested on IBM zSystems.  Ok for mainline?
> 
> gcc/ChangeLog:
> 
> 	* config/s390/s390.cc (s390_bb_fallthru_entry_likely): Remove.
> 	(struct s390_sched_state): Initialise to zero.
> 	(s390_sched_variable_issue): For better debuggability also emit
> 	the current side.
> 	(s390_sched_init): Unconditionally reset scheduler state.

Ok. Thanks!

Andreas