re PR tree-optimization/15993 ([lno] Compiler hangs at -O3)

	PR tree-optimization/15993
	* tree-ssa-dom.c (thread_across_edge): Do not thread edge if its
	destination is unchanged.

From-SVN: r83242

gcc/tree-ssa-dom.c

@@ -924,7 +924,7 @@ thread_across_edge (struct dom_walk_data *walk_data, edge e)
 	  edge taken_edge = find_taken_edge (e->dest, cached_lhs);
 	  basic_block dest = (taken_edge ? taken_edge->dest : NULL);
 
-	  if (dest == e->src)
+	  if (dest == e->dest)
 	    return;
 
 	  /* If we have a known destination for the conditional, then