dominance.c fix to not access undefined memory location.

[Steve Ellcey]

I was running a memory checker on GCC and noticed that the if statements
below were accessing undefined memory locations because if bn was
ex_block then bn->index would be -1 or -2 and di->dfs_order[bn->index]
would be an out-of-bounds array reference.  By checking for ex_block
first we can avoid that.


2001-07-12  Steve Ellcey <sje@cup.hp.com>

	* dominance.c (calc_dfs_tree_nonrec): Reverse order of tests
	in if statement so we don't access undefined memory.


*** gcc/dominance.c.orig	Thu Jul 12 13:59:29 2001
--- gcc/dominance.c	Thu Jul 12 14:02:14 2001
*************** calc_dfs_tree_nonrec (di, bb, reverse)
*** 242,248 ****
  	      /* If the next node BN is either already visited or a border
  	         block the current edge is useless, and simply overwritten
  	         with the next edge out of the current node.  */
! 	      if (di->dfs_order[bn->index] || bn == ex_block)
  		{
  		  e = e->pred_next;
  		  continue;
--- 242,248 ----
  	      /* If the next node BN is either already visited or a border
  	         block the current edge is useless, and simply overwritten
  	         with the next edge out of the current node.  */
! 	      if (bn == ex_block || di->dfs_order[bn->index])
  		{
  		  e = e->pred_next;
  		  continue;
*************** calc_dfs_tree_nonrec (di, bb, reverse)
*** 253,259 ****
  	  else
  	    {
  	      bn = e->dest;
! 	      if (di->dfs_order[bn->index] || bn == ex_block)
  		{
  		  e = e->succ_next;
  		  continue;
--- 253,259 ----
  	  else
  	    {
  	      bn = e->dest;
! 	      if (bn == ex_block || di->dfs_order[bn->index])
  		{
  		  e = e->succ_next;
  		  continue;