diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 41aa22178fb..f5ec63af82b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2006-09-13  Jan Hubicka  <jh@suse.cz>
+
+	* cfganal.c (compute_dominance_frontiers_1): Don't be quadratic.
+
 2006-09-12  Eric Botcazou  <ebotcazou@libertysurf.fr>
 
 	PR rtl-optimization/28243
diff --git a/gcc/cfganal.c b/gcc/cfganal.c
index 835703fe8cf..467c399c84c 100644
--- a/gcc/cfganal.c
+++ b/gcc/cfganal.c
@@ -1054,6 +1054,8 @@ compute_dominance_frontiers_1 (bitmap *frontiers)
 	      domsb = get_immediate_dominator (CDI_DOMINATORS, b);
 	      while (runner != domsb)
 		{
+		  if (bitmap_bit_p (frontiers[runner->index], b->index))
+		    break;
 		  bitmap_set_bit (frontiers[runner->index],
 				  b->index);
 		  runner = get_immediate_dominator (CDI_DOMINATORS,