[tree-ssa] Return an edge if true and false edge of a branch are the same

[Steven Bosscher <stevenb at suse dot de>]

Hi,

When I was working on DCE I noticed that in cleanup_cfg we don't always
remove conditional branches that lead to the same target block.

Bootstrapped&tested on i686-pc-linux-gnu, OK?

Gr.
Steven


	* tree-flow.h (cleanup_control_expr_graph): Don't declare here.
	* tree-cfg.c (cleanup_control_expr_graph): Make static.
	(find_edge_taken_cond_expr): Return an edge if the true and false
	edges of a branch lead to the same basic block.

Index: tree-cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/tree-cfg.c,v
retrieving revision 1.1.4.267
diff -c -3 -p -r1.1.4.267 tree-cfg.c
*** tree-cfg.c	13 Feb 2004 00:10:25 -0000	1.1.4.267
--- tree-cfg.c	15 Feb 2004 11:29:19 -0000
*************** static void tree_merge_blocks (basic_blo
*** 111,116 ****
--- 111,117 ----
  static bool tree_can_merge_blocks_p (basic_block, basic_block);
  static void remove_bb (basic_block);
  static bool cleanup_control_flow (void);
+ static bool cleanup_control_expr_graph (basic_block, block_stmt_iterator);
  static edge find_taken_edge_cond_expr (basic_block, tree);
  static edge find_taken_edge_switch_expr (basic_block, tree);
  static tree find_case_label_for_value (tree, tree);
*************** cleanup_control_flow (void)
*** 1626,1632 ****
  /* Disconnect an unreachable block in the control expression starting
     at block BB.  */
  
! bool
  cleanup_control_expr_graph (basic_block bb, block_stmt_iterator bsi)
  {
    edge taken_edge;
--- 1627,1633 ----
  /* Disconnect an unreachable block in the control expression starting
     at block BB.  */
  
! static bool
  cleanup_control_expr_graph (basic_block bb, block_stmt_iterator bsi)
  {
    edge taken_edge;
*************** find_taken_edge (basic_block bb, tree va
*** 1718,1744 ****
  static edge
  find_taken_edge_cond_expr (basic_block bb, tree val)
  {
!   bool always_false;
!   bool always_true;
!   edge e;
  
!   /* Determine which branch of the if() will be taken.  */
!   always_false = integer_zerop (val);
!   always_true = integer_nonzerop (val);
  
!   /* If VAL is a constant but it can't be reduced to a 0 or a 1, then
       we don't really know which edge will be taken at runtime.  This
!      may happen when comparing addresses (e.g., if (&var1 == 4))  */
!   if (!always_false && !always_true)
      return NULL;
- 
-   for (e = bb->succ; e; e = e->succ_next)
-     if (((e->flags & EDGE_TRUE_VALUE) && always_true)
- 	|| ((e->flags & EDGE_FALSE_VALUE) && always_false))
-       return e;
- 
-   /* There always should be an edge that is taken.  */
-   abort ();
  }
  
  /* Given a constant value VAL and the entry block BB to a SWITCH_EXPR
--- 1719,1743 ----
  static edge
  find_taken_edge_cond_expr (basic_block bb, tree val)
  {
!   edge true_edge, false_edge;
! 
!   extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
  
!   /* If both edges of the branch lead to the same basic block, it doesn't
!      matter which edge is taken.  */
!   if (true_edge->dest == false_edge->dest)
!     return true_edge;
  
!   /* Otherwise, try to determine which branch of the if() will be taken.
!      If VAL is a constant but it can't be reduced to a 0 or a 1, then
       we don't really know which edge will be taken at runtime.  This
!      may happen when comparing addresses (e.g., if (&var1 == 4)).  */
!   if (integer_nonzerop (val))
!     return true_edge;
!   else if (integer_zerop (val))
!     return false_edge;
!   else
      return NULL;
  }
  
  /* Given a constant value VAL and the entry block BB to a SWITCH_EXPR
Index: tree-flow.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/tree-flow.h,v
retrieving revision 1.1.4.187
diff -c -3 -p -r1.1.4.187 tree-flow.h
*** tree-flow.h	13 Feb 2004 11:15:56 -0000	1.1.4.187
--- tree-flow.h	15 Feb 2004 11:29:20 -0000
*************** extern edge find_taken_edge (basic_block
*** 468,474 ****
  extern void cfg_remove_useless_stmts (void);
  extern edge thread_edge (edge, basic_block);
  extern basic_block label_to_block (tree);
- extern bool cleanup_control_expr_graph (basic_block, block_stmt_iterator);
  extern void tree_optimize_tail_calls (bool, enum tree_dump_index);
  extern edge tree_block_forwards_to (basic_block bb);
  extern void bsi_insert_on_edge (edge, tree);
--- 468,473 ----