[tree-ssa] Fix unfactoring of computed gotos

[Zdenek Dvorak]

Hello,

the current way factored computed gotos are unfactored is broken,
since there is no guarantee that no code will be emitted between
factored_computed_goto_label and factored_computed_goto.

I don't have a testcase (it happed to me just on lno-branch, where
store motion may expose it) and it is possible that it indeed cannot
be reproduced with the clean tree-ssa branch.

Bootstrapped & regtested on i686.

Zdenek

	* tree-cfg.c (factored_computed_goto_label,
	factored_computed_goto): Removed.
	(disband_implicit_edges): Unfactor computed gotos without
	using them.

Index: tree-cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/tree-cfg.c,v
retrieving revision 1.1.4.280
diff -c -3 -p -r1.1.4.280 tree-cfg.c
*** tree-cfg.c	3 Apr 2004 11:12:00 -0000	1.1.4.280
--- tree-cfg.c	21 Apr 2004 20:47:27 -0000
*************** static struct cfg_stats_d cfg_stats;
*** 67,81 ****
  /* Nonzero if we found a computed goto while building basic blocks.  */
  static bool found_computed_goto;
  
- /* If we found computed gotos, then they are all revectored to this
-    location.  We try to unfactor them after we have translated out
-    of SSA form.  */
- static GTY(()) tree factored_computed_goto_label;
- 
- /* The factored computed goto.  We cache this so we can easily recover
-    the destination of computed gotos when unfactoring them.  */
- static GTY(()) tree factored_computed_goto;
- 
  /* Basic blocks and flowgraphs.  */
  static basic_block create_bb (void *, void *, basic_block);
  static void create_block_annotation (basic_block);
--- 67,72 ----
*************** factor_computed_gotos (void)
*** 223,228 ****
--- 213,220 ----
    basic_block bb;
    tree factored_label_decl = NULL;
    tree var = NULL;
+   tree factored_computed_goto_label = NULL;
+   tree factored_computed_goto = NULL;
  
    /* We know there are one or more computed gotos in this function.
       Examine the last statement in each basic block to see if the block
*************** disband_implicit_edges (void)
*** 2457,2463 ****
    basic_block bb;
    block_stmt_iterator last;
    edge e;
!   tree stmt, label;
  
    FOR_EACH_BB (bb)
      {
--- 2449,2455 ----
    basic_block bb;
    block_stmt_iterator last;
    edge e;
!   tree stmt, label, forward;
  
    FOR_EACH_BB (bb)
      {
*************** disband_implicit_edges (void)
*** 2524,2543 ****
  
        label = tree_block_label (e->dest);
  
!       /* ??? Why bother putting this back together when rtl is just
  	 about to take it apart again?  */
!       if (factored_computed_goto_label
! 	  && label == LABEL_EXPR_LABEL (factored_computed_goto_label))
! 	label = GOTO_DESTINATION (factored_computed_goto);
  
        bsi_insert_after (&last,
  			build1 (GOTO_EXPR, void_type_node, label),
  			BSI_NEW_STMT);
        e->flags &= ~EDGE_FALLTHRU;
      }
- 
-   factored_computed_goto = NULL;
-   factored_computed_goto_label = NULL;
  }
  
  
--- 2516,2535 ----
  
        label = tree_block_label (e->dest);
  
!       /* If this is a goto to a goto, jump to the final destination.
!          Handles unfactoring of the computed jumps.
!          ??? Why bother putting this back together when rtl is just
  	 about to take it apart again?  */
!       forward = last_and_only_stmt (e->dest);
!       if (forward
! 	  && TREE_CODE (forward) == GOTO_EXPR)
! 	label = GOTO_DESTINATION (forward);
  
        bsi_insert_after (&last,
  			build1 (GOTO_EXPR, void_type_node, label),
  			BSI_NEW_STMT);
        e->flags &= ~EDGE_FALLTHRU;
      }
  }