[PATCH] PR85964

[Richard Biener]

This makes tracer not explode with -fno-guess-branch-probabilities.
I've settled with find_best_successor/predecessor not returning
anything if _any_ edge in the interesting direction doesn't have
->count () initialized (rather than ignoring such edges).

Honza - I suppose it is on purpose that functions like
.to_frequency () do not ICE for uninitialized counters?
It at least looks like "previous" behavior was more sane
for tracer in the counts/frequencies that were exposed.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Honza, does this look OK to you?

tracer going wild on this testcase exposes the CFG cleanup
scalability issue I've posted the following RFC for:
https://gcc.gnu.org/ml/gcc-patches/2018-05/msg01644.html

Thanks,
Richard.

2018-05-30  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/85964
	* tracer.c (better_p): Drop initialized count check, we only
	call the function with initialized counts now.
	(find_best_successor): Do find a best edge if one
	has uninitialized count.
	(find_best_predecessor): Likewise.  Do BB frequency check only
	if count is initialized.

Index: gcc/tracer.c
===================================================================
--- gcc/tracer.c	(revision 260896)
+++ gcc/tracer.c	(working copy)
@@ -132,8 +132,7 @@ count_insns (basic_block bb)
 static bool
 better_p (const_edge e1, const_edge e2)
 {
-  if (e1->count ().initialized_p () && e2->count ().initialized_p ()
-      && ((e1->count () > e2->count ()) || (e1->count () < e2->count  ())))
+  if ((e1->count () > e2->count ()) || (e1->count () < e2->count ()))
     return e1->count () > e2->count ();
   /* This is needed to avoid changes in the decision after
      CFG is modified.  */
@@ -152,12 +151,15 @@ find_best_successor (basic_block bb)
   edge_iterator ei;
 
   FOR_EACH_EDGE (e, ei, bb->succs)
-    if (!best || better_p (e, best))
-      best = e;
+    {
+      if (!e->count ().initialized_p ())
+	return NULL;
+      if (!best || better_p (e, best))
+	best = e;
+    }
   if (!best || ignore_bb_p (best->dest))
     return NULL;
-  if (best->probability.initialized_p ()
-      && best->probability.to_reg_br_prob_base () <= probability_cutoff)
+  if (best->probability.to_reg_br_prob_base () <= probability_cutoff)
     return NULL;
   return best;
 }
@@ -172,12 +174,17 @@ find_best_predecessor (basic_block bb)
   edge_iterator ei;
 
   FOR_EACH_EDGE (e, ei, bb->preds)
-    if (!best || better_p (e, best))
-      best = e;
+    {
+      if (!e->count ().initialized_p ())
+	return NULL;
+      if (!best || better_p (e, best))
+	best = e;
+    }
   if (!best || ignore_bb_p (best->src))
     return NULL;
-  if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
-      < bb->count.to_frequency (cfun) * branch_ratio_cutoff)
+  if (bb->count.initialized_p ()
+      && (best->count ().to_frequency (cfun) * REG_BR_PROB_BASE
+	  < bb->count.to_frequency (cfun) * branch_ratio_cutoff))
     return NULL;
   return best;
 }