re PR tree-optimization/18815 (Tree if-conversion screws up cfg very badly)

       PR tree-optimization/18815
       * tree-if-conv.c (combine_blocks): Adjust loop header edges for
       loops with zero exit edges.

From-SVN: r95923

gcc/ChangeLog

 2005-03-04  Devang Patel  <dpatel@apple.com>
+	
+	PR tree-optimization/18815
+	* tree-if-conv.c (combine_blocks): Adjust loop header edges for
+	loops with zero exit edges.
+
+2005-03-04  Devang Patel  <dpatel@apple.com>
 
 	* doc/invoke.texi: Remove reference to webpage that does not exist.
 	

gcc/tree-if-conv.c

@@ -858,7 +858,8 @@ combine_blocks (struct loop *loop)
   basic_block bb, exit_bb, merge_target_bb;
   unsigned int orig_loop_num_nodes = loop->num_nodes;
   unsigned int i;
-
+  unsigned int n_exits;
+  edge *exits = get_loop_exit_edges (loop, &n_exits);
   /* Process phi nodes to prepare blocks for merge.  */
   process_phi_nodes (loop);
 
@@ -905,11 +906,23 @@ combine_blocks (struct loop *loop)
 	continue;
 
       /* It is time to remove this basic block.	 First remove edges.  */
-      while (EDGE_COUNT (bb->succs) > 0)
-	remove_edge (EDGE_SUCC (bb, 0));
       while (EDGE_COUNT (bb->preds) > 0)
 	remove_edge (EDGE_PRED (bb, 0));
 
+      /* This is loop latch and loop does not have exit then do not
+ 	 delete this basic block. Just remove its PREDS and reconnect 
+ 	 loop->header and loop->latch blocks.  */
+      if (bb == loop->latch && n_exits == 0)
+ 	{
+	  exits = NULL; /* To suppress unused warning.  */
+ 	  make_edge (loop->header, loop->latch, EDGE_FALLTHRU);
+ 	  set_immediate_dominator (CDI_DOMINATORS, loop->latch, loop->header);
+	  continue;
+ 	}
+
+      while (EDGE_COUNT (bb->succs) > 0)
+	remove_edge (EDGE_SUCC (bb, 0));
+
       /* Remove labels and make stmts member of loop->header.  */
       for (bsi = bsi_start (bb); !bsi_end_p (bsi); )
 	{