tree-ssa-ifcombine.c (update_profile_after_ifcombine): Handle profile_probability::always better.

	* tree-ssa-ifcombine.c (update_profile_after_ifcombine): Handle
	profile_probability::always better.

From-SVN: r266585

gcc/ChangeLog

 2018-11-28  Jan Hubicka  <jh@suse.cz>
 
+	* tree-ssa-ifcombine.c (update_profile_after_ifcombine): Handle
+	profile_probability::always better.
+
+2018-11-28  Jan Hubicka  <jh@suse.cz>
+
 	* profile-count.h (profile_count::split): Give better result when
 	splitting profile_probability::always.
 

gcc/tree-ssa-ifcombine.c

@@ -360,8 +360,15 @@ update_profile_after_ifcombine (basic_block inner_cond_bb,
 
   inner_cond_bb->count = outer_cond_bb->count;
 
-  inner_taken->probability = outer2->probability + outer_to_inner->probability
-			     * inner_taken->probability;
+  /* Handle special case where inner_taken probability is always. In this case
+     we know that the overall outcome will be always as well, but combining
+     probabilities will be conservative because it does not know that
+     outer2->probability is inverse of outer_to_inner->probability.  */
+  if (inner_taken->probability == profile_probability::always ())
+    ;
+  else
+    inner_taken->probability = outer2->probability + outer_to_inner->probability
+			       * inner_taken->probability;
   inner_not_taken->probability = profile_probability::always ()
 				 - inner_taken->probability;