Improve force_edge_cold

[Jan Hubicka]

Hi,
force_edge_cold can be more aggressive about propagating zero counts.

Honza

Bootstrapped/regtested x86_64-linux, will commit it later today.

        * predict.c (force_edge_cold): Handle declaring edges impossible
        more aggresively.
Index: predict.c
===================================================================
--- predict.c   (revision 249244)
+++ predict.c   (working copy)
@@ -3968,6 +3968,7 @@ force_edge_cold (edge e, bool impossible
   profile_count old_count = e->count;
   int old_probability = e->probability;
   int prob_scale = REG_BR_PROB_BASE;
+  bool uninitialized_exit = false;
 
   /* If edge is already improbably or cold, just return.  */
   if (e->probability <= (impossible ? PROB_VERY_UNLIKELY : 0)
@@ -3978,6 +3979,8 @@ force_edge_cold (edge e, bool impossible
       {
        if (e2->count.initialized_p ())
          count_sum += e2->count;
+       else
+         uninitialized_exit = true;
        prob_sum += e2->probability;
       }
 
@@ -3989,7 +3992,7 @@ force_edge_cold (edge e, bool impossible
         = MIN (e->probability, impossible ? 0 : PROB_VERY_UNLIKELY);
       if (impossible)
        e->count = profile_count::zero ();
-      if (old_probability)
+      else if (old_probability)
        e->count = e->count.apply_scale (e->probability, old_probability);
       else
         e->count = e->count.apply_scale (1, REG_BR_PROB_BASE);
@@ -4016,6 +4019,34 @@ force_edge_cold (edge e, bool impossible
   else
     {
       e->probability = REG_BR_PROB_BASE;
+      if (e->src->count == profile_count::zero ())
+       return;
+      if (count_sum == profile_count::zero () && !uninitialized_exit
+         && impossible)
+       {
+         bool found = false;
+         for (gimple_stmt_iterator gsi = gsi_start_bb (e->src);
+              !gsi_end_p (gsi); gsi_next (&gsi))
+           {
+             if (stmt_can_terminate_bb_p (gsi_stmt (gsi)))
+               {
+                 found = true;
+                 break;
+               }
+           }
+         if (!found)
+           {
+             if (dump_file && (dump_flags & TDF_DETAILS))
+               fprintf (dump_file,
+                        "Making bb %i impossible and dropping count to 0.\n",
+                        e->src->index);
+             e->count = profile_count::zero ();
+             e->src->count = profile_count::zero ();
+             FOR_EACH_EDGE (e2, ei, e->src->preds)
+               force_edge_cold (e2, impossible);
+             return;
+           }
+       }
 
       /* If we did not adjusting, the source basic block has no likely edeges
         leaving other direction. In that case force that bb cold, too.