text: /* Exception handling semantics and decomposition for trees.
     Copyright (C) 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
  
  This file is part of GCC.
  
  GCC is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 3, or (at your option)
  any later version.
  
  GCC is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with GCC; see the file COPYING3.  If not see
  <http://www.gnu.org/licenses/>.  */
  
  #include "config.h"
  #include "system.h"
  #include "coretypes.h"
  #include "tm.h"
  #include "tree.h"
  #include "rtl.h"
  #include "tm_p.h"
  #include "flags.h"
  #include "function.h"
  #include "except.h"
  #include "tree-flow.h"
  #include "tree-dump.h"
  #include "tree-inline.h"
  #include "tree-iterator.h"
  #include "tree-pass.h"
  #include "timevar.h"
  #include "langhooks.h"
  #include "ggc.h"
  #include "toplev.h"
  #include "pointer-set.h"
  
  
  /* Nonzero if we are using EH to handle cleanups.  */
  static int using_eh_for_cleanups_p = 0;
  
  void
  using_eh_for_cleanups (void)
  {
    using_eh_for_cleanups_p = 1;
  }
  
  /* Misc functions used in this file.  */
  
  /* Compare and hash for any structure which begins with a canonical
     pointer.  Assumes all pointers are interchangeable, which is sort
     of already assumed by gcc elsewhere IIRC.  */
  
  static int
  struct_ptr_eq (const void *a, const void *b)
  {
    const void * const * x = (const void * const *) a;
    const void * const * y = (const void * const *) b;
    return *x == *y;
  }
  
  static hashval_t
  struct_ptr_hash (const void *a)
  {
    const void * const * x = (const void * const *) a;
    return (size_t)*x >> 4;
  }
  
  
  /* Remember and lookup EH region data for arbitrary statements.
     Really this means any statement that could_throw_p.  We could
     stuff this information into the stmt_ann data structure, but:
  
     (1) We absolutely rely on this information being kept until
     we get to rtl.  Once we're done with lowering here, if we lose
     the information there's no way to recover it!
  
     (2) There are many more statements that *cannot* throw as
     compared to those that can.  We should be saving some amount
     of space by only allocating memory for those that can throw.  */
  
  static void
  record_stmt_eh_region (struct eh_region *region, tree t)
  {
    if (!region)
      return;
  
    add_stmt_to_eh_region (t, get_eh_region_number (region));
  }
  
  void
  add_stmt_to_eh_region_fn (struct function *ifun, tree t, int num)
  {
    struct throw_stmt_node *n;
    void **slot;
  
    gcc_assert (num >= 0);
    gcc_assert (TREE_CODE (t) != RESX_EXPR);
  
    n = GGC_NEW (struct throw_stmt_node);
    n->stmt = t;
    n->region_nr = num;
  
    if (!get_eh_throw_stmt_table (ifun))
      set_eh_throw_stmt_table (ifun, htab_create_ggc (31, struct_ptr_hash,
  						    struct_ptr_eq,
  						    ggc_free));
  
    slot = htab_find_slot (get_eh_throw_stmt_table (ifun), n, INSERT);
    gcc_assert (!*slot);
    *slot = n;
  }
  
  void
  add_stmt_to_eh_region (tree t, int num)
  {
    add_stmt_to_eh_region_fn (cfun, t, num);
  }
  
  bool
  remove_stmt_from_eh_region_fn (struct function *ifun, tree t)
  {
    struct throw_stmt_node dummy;
    void **slot;
  
    if (!get_eh_throw_stmt_table (ifun))
      return false;
  
    dummy.stmt = t;
    slot = htab_find_slot (get_eh_throw_stmt_table (ifun), &dummy,
                          NO_INSERT);
    if (slot)
      {
        htab_clear_slot (get_eh_throw_stmt_table (ifun), slot);
        return true;
      }
    else
      return false;
  }
  
  bool
  remove_stmt_from_eh_region (tree t)
  {
    return remove_stmt_from_eh_region_fn (cfun, t);
  }
  
  int
  lookup_stmt_eh_region_fn (struct function *ifun, const_tree t)
  {
    struct throw_stmt_node *p, n;
  
    if (!get_eh_throw_stmt_table (ifun))
      return -2;
  
    /* The CONST_CAST is okay because we don't modify n.stmt throughout
       its scope, or the scope of p.  */
    n.stmt = CONST_CAST_TREE (t);
    p = (struct throw_stmt_node *) htab_find (get_eh_throw_stmt_table (ifun),
                                              &n);
  
    return (p ? p->region_nr : -1);
  }
  
  int
  lookup_stmt_eh_region (const_tree t)
  {
    /* We can get called from initialized data when -fnon-call-exceptions
       is on; prevent crash.  */
    if (!cfun)
      return -1;
    return lookup_stmt_eh_region_fn (cfun, t);
  }
  
  
  /* First pass of EH node decomposition.  Build up a tree of TRY_FINALLY_EXPR
     nodes and LABEL_DECL nodes.  We will use this during the second phase to
     determine if a goto leaves the body of a TRY_FINALLY_EXPR node.  */
  
  struct finally_tree_node
  {
    tree child, parent;
  };
  
  /* Note that this table is *not* marked GTY.  It is short-lived.  */
  static htab_t finally_tree;
  
  static void
  record_in_finally_tree (tree child, tree parent)
  {
    struct finally_tree_node *n;
    void **slot;
  
    n = XNEW (struct finally_tree_node);
    n->child = child;
    n->parent = parent;
  
    slot = htab_find_slot (finally_tree, n, INSERT);
    gcc_assert (!*slot);
    *slot = n;
  }
  
  static void
  collect_finally_tree (tree t, tree region)
  {
   tailrecurse:
    switch (TREE_CODE (t))
      {
      case LABEL_EXPR:
        record_in_finally_tree (LABEL_EXPR_LABEL (t), region);
        break;
  
      case TRY_FINALLY_EXPR:
        record_in_finally_tree (t, region);
        collect_finally_tree (TREE_OPERAND (t, 0), t);
        t = TREE_OPERAND (t, 1);
        goto tailrecurse;
  
      case TRY_CATCH_EXPR:
        collect_finally_tree (TREE_OPERAND (t, 0), region);
        t = TREE_OPERAND (t, 1);
        goto tailrecurse;
  
      case CATCH_EXPR:
        t = CATCH_BODY (t);
        goto tailrecurse;
  
      case EH_FILTER_EXPR:
        t = EH_FILTER_FAILURE (t);
        goto tailrecurse;
  
      case STATEMENT_LIST:
        {
  	tree_stmt_iterator i;
  	for (i = tsi_start (t); !tsi_end_p (i); tsi_next (&i))
  	  collect_finally_tree (tsi_stmt (i), region);
        }
        break;
  
      default:
        /* A type, a decl, or some kind of statement that we're not
  	 interested in.  Don't walk them.  */
        break;
      }
  }
  
  /* Use the finally tree to determine if a jump from START to TARGET
     would leave the try_finally node that START lives in.  */
  
  static bool
  outside_finally_tree (tree start, tree target)
  {
    struct finally_tree_node n, *p;
  
    do
      {
        n.child = start;
        p = (struct finally_tree_node *) htab_find (finally_tree, &n);
        if (!p)
  	return true;
        start = p->parent;
      }
    while (start != target);
  
    return false;
  }
  
  /* Second pass of EH node decomposition.  Actually transform the TRY_FINALLY
     and TRY_CATCH nodes into a set of gotos, magic labels, and eh regions.
     The eh region creation is straight-forward, but frobbing all the gotos
     and such into shape isn't.  */
  
  /* State of the world while lowering.  */
  
  struct leh_state
  {
    /* What's "current" while constructing the eh region tree.  These
       correspond to variables of the same name in cfun->eh, which we
       don't have easy access to.  */
    struct eh_region *cur_region;
    struct eh_region *prev_try;
  
    /* Processing of TRY_FINALLY requires a bit more state.  This is
       split out into a separate structure so that we don't have to
       copy so much when processing other nodes.  */
    struct leh_tf_state *tf;
  };
  
  struct leh_tf_state
  {
    /* Pointer to the TRY_FINALLY node under discussion.  The try_finally_expr
       is the original TRY_FINALLY_EXPR.  We need to retain this so that
       outside_finally_tree can reliably reference the tree used in the
       collect_finally_tree data structures.  */
    tree try_finally_expr;
    tree *top_p;
  
    /* The state outside this try_finally node.  */
    struct leh_state *outer;
  
    /* The exception region created for it.  */
    struct eh_region *region;
  
    /* The GOTO_QUEUE is is an array of GOTO_EXPR and RETURN_EXPR statements
       that are seen to escape this TRY_FINALLY_EXPR node.  */
    struct goto_queue_node {
      tree stmt;
      tree repl_stmt;
      tree cont_stmt;
      int index;
    } *goto_queue;
    size_t goto_queue_size;
    size_t goto_queue_active;
  
    /* Pointer map to help in searching qoto_queue when it is large.  */
    struct pointer_map_t *goto_queue_map;
  
    /* The set of unique labels seen as entries in the goto queue.  */
    VEC(tree,heap) *dest_array;
  
    /* A label to be added at the end of the completed transformed
       sequence.  It will be set if may_fallthru was true *at one time*,
       though subsequent transformations may have cleared that flag.  */
    tree fallthru_label;
  
    /* A label that has been registered with except.c to be the
       landing pad for this try block.  */
    tree eh_label;
  
    /* True if it is possible to fall out the bottom of the try block.
       Cleared if the fallthru is converted to a goto.  */
    bool may_fallthru;
  
    /* True if any entry in goto_queue is a RETURN_EXPR.  */
    bool may_return;
  
    /* True if the finally block can receive an exception edge.
       Cleared if the exception case is handled by code duplication.  */
    bool may_throw;
  };
  
  static void lower_eh_filter (struct leh_state *, tree *);
  static void lower_eh_constructs_1 (struct leh_state *, tree *);
  
  /* Search for STMT in the goto queue.  Return the replacement,
     or null if the statement isn't in the queue.  */
  
  #define LARGE_GOTO_QUEUE 20
  
  static tree
  find_goto_replacement (struct leh_tf_state *tf, tree stmt)
  {
    unsigned int i;
    void **slot;
  
    if (tf->goto_queue_active < LARGE_GOTO_QUEUE)
      {
        for (i = 0; i < tf->goto_queue_active; i++)
  	if (tf->goto_queue[i].stmt == stmt)
  	  return tf->goto_queue[i].repl_stmt;
        return NULL;
      }
  
    /* If we have a large number of entries in the goto_queue, create a
       pointer map and use that for searching.  */
  
    if (!tf->goto_queue_map)
      {
        tf->goto_queue_map = pointer_map_create ();
        for (i = 0; i < tf->goto_queue_active; i++)
  	{
  	  slot = pointer_map_insert (tf->goto_queue_map, tf->goto_queue[i].stmt);
            gcc_assert (*slot == NULL);
  	  *slot = (void *) &tf->goto_queue[i];
  	}
      }
  
    slot = pointer_map_contains (tf->goto_queue_map, stmt);
    if (slot != NULL)
      return (((struct goto_queue_node *) *slot)->repl_stmt);
  
    return NULL;
  }
  
  /* A subroutine of replace_goto_queue_1.  Handles the sub-clauses of a
     lowered COND_EXPR.  If, by chance, the replacement is a simple goto,
     then we can just splat it in, otherwise we add the new stmts immediately
     after the COND_EXPR and redirect.  */
  
  static void
  replace_goto_queue_cond_clause (tree *tp, struct leh_tf_state *tf,
  				tree_stmt_iterator *tsi)
  {
    tree new, one, label;
  
    new = find_goto_replacement (tf, *tp);
    if (!new)
      return;
  
    one = expr_only (new);
    if (one && TREE_CODE (one) == GOTO_EXPR)
      {
        *tp = one;
        return;
      }
  
    label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
    *tp = build_and_jump (&LABEL_EXPR_LABEL (label));
  
    tsi_link_after (tsi, label, TSI_CONTINUE_LINKING);
    tsi_link_after (tsi, new, TSI_CONTINUE_LINKING);
  }
  
  /* The real work of replace_goto_queue.  Returns with TSI updated to
     point to the next statement.  */
  
  static void replace_goto_queue_stmt_list (tree, struct leh_tf_state *);
  
  static void
  replace_goto_queue_1 (tree t, struct leh_tf_state *tf, tree_stmt_iterator *tsi)
  {
    switch (TREE_CODE (t))
      {
      case GOTO_EXPR:
      case RETURN_EXPR:
        t = find_goto_replacement (tf, t);
        if (t)
  	{
  	  tsi_link_before (tsi, t, TSI_SAME_STMT);
  	  tsi_delink (tsi);
  	  return;
  	}
        break;
  
      case COND_EXPR:
        replace_goto_queue_cond_clause (&COND_EXPR_THEN (t), tf, tsi);
        replace_goto_queue_cond_clause (&COND_EXPR_ELSE (t), tf, tsi);
        break;
  
      case TRY_FINALLY_EXPR:
      case TRY_CATCH_EXPR:
        replace_goto_queue_stmt_list (TREE_OPERAND (t, 0), tf);
        replace_goto_queue_stmt_list (TREE_OPERAND (t, 1), tf);
        break;
      case CATCH_EXPR:
        replace_goto_queue_stmt_list (CATCH_BODY (t), tf);
        break;
      case EH_FILTER_EXPR:
        replace_goto_queue_stmt_list (EH_FILTER_FAILURE (t), tf);
        break;
  
      case STATEMENT_LIST:
        gcc_unreachable ();
  
      default:
        /* These won't have gotos in them.  */
        break;
      }
  
    tsi_next (tsi);
  }
  
  /* A subroutine of replace_goto_queue.  Handles STATEMENT_LISTs.  */
  
  static void
  replace_goto_queue_stmt_list (tree t, struct leh_tf_state *tf)
  {
    tree_stmt_iterator i = tsi_start (t);
    while (!tsi_end_p (i))
      replace_goto_queue_1 (tsi_stmt (i), tf, &i);
  }
  
  /* Replace all goto queue members.  */
  
  static void
  replace_goto_queue (struct leh_tf_state *tf)
  {
    if (tf->goto_queue_active == 0)
      return;
    replace_goto_queue_stmt_list (*tf->top_p, tf);
  }
  
  /* For any GOTO_EXPR or RETURN_EXPR, decide whether it leaves a try_finally
     node, and if so record that fact in the goto queue associated with that
     try_finally node.  */
  
  static void
  maybe_record_in_goto_queue (struct leh_state *state, tree stmt)
  {
    struct leh_tf_state *tf = state->tf;
    struct goto_queue_node *q;
    size_t active, size;
    int index;
  
    if (!tf)
      return;
  
    switch (TREE_CODE (stmt))
      {
      case GOTO_EXPR:
        {
  	tree lab = GOTO_DESTINATION (stmt);
  
  	/* Computed and non-local gotos do not get processed.  Given
  	   their nature we can neither tell whether we've escaped the
  	   finally block nor redirect them if we knew.  */
  	if (TREE_CODE (lab) != LABEL_DECL)
  	  return;
  
  	/* No need to record gotos that don't leave the try block.  */
  	if (! outside_finally_tree (lab, tf->try_finally_expr))
  	  return;
  
  	if (! tf->dest_array)
  	  {
  	    tf->dest_array = VEC_alloc (tree, heap, 10);
  	    VEC_quick_push (tree, tf->dest_array, lab);
  	    index = 0;
  	  }
  	else
  	  {
  	    int n = VEC_length (tree, tf->dest_array);
  	    for (index = 0; index < n; ++index)
  	      if (VEC_index (tree, tf->dest_array, index) == lab)
  		break;
  	    if (index == n)
  	      VEC_safe_push (tree, heap, tf->dest_array, lab);
  	  }
        }
        break;
  
      case RETURN_EXPR:
        tf->may_return = true;
        index = -1;
        break;
  
      default:
        gcc_unreachable ();
      }
  
    gcc_assert (!tf->goto_queue_map);
  
    active = tf->goto_queue_active;
    size = tf->goto_queue_size;
    if (active >= size)
      {
        size = (size ? size * 2 : 32);
        tf->goto_queue_size = size;
        tf->goto_queue
           = XRESIZEVEC (struct goto_queue_node, tf->goto_queue, size);
      }
  
    q = &tf->goto_queue[active];
    tf->goto_queue_active = active + 1;
  
    memset (q, 0, sizeof (*q));
    q->stmt = stmt;
    q->index = index;
  }
  
  #ifdef ENABLE_CHECKING
  /* We do not process SWITCH_EXPRs for now.  As long as the original source
     was in fact structured, and we've not yet done jump threading, then none
     of the labels will leave outer TRY_FINALLY_EXPRs.  Verify this.  */
  
  static void
  verify_norecord_switch_expr (struct leh_state *state, tree switch_expr)
  {
    struct leh_tf_state *tf = state->tf;
    size_t i, n;
    tree vec;
  
    if (!tf)
      return;
  
    vec = SWITCH_LABELS (switch_expr);
    n = TREE_VEC_LENGTH (vec);
  
    for (i = 0; i < n; ++i)
      {
        tree lab = CASE_LABEL (TREE_VEC_ELT (vec, i));
        gcc_assert (!outside_finally_tree (lab, tf->try_finally_expr));
      }
  }
  #else
  #define verify_norecord_switch_expr(state, switch_expr)
  #endif
  
  /* Redirect a RETURN_EXPR pointed to by STMT_P to FINLAB.  Place in CONT_P
     whatever is needed to finish the return.  If MOD is non-null, insert it
     before the new branch.  RETURN_VALUE_P is a cache containing a temporary
     variable to be used in manipulating the value returned from the function.  */
  
  static void
  do_return_redirection (struct goto_queue_node *q, tree finlab, tree mod,
  		       tree *return_value_p)
  {
    tree ret_expr = TREE_OPERAND (q->stmt, 0);
    tree x;
  
    if (ret_expr)
      {
        /* The nasty part about redirecting the return value is that the
  	 return value itself is to be computed before the FINALLY block
  	 is executed.  e.g.
  
  		int x;
  		int foo (void)
  		{
  		  x = 0;
  		  try {
  		    return x;
  		  } finally {
  		    x++;
  		  }
  		}
  
  	  should return 0, not 1.  Arrange for this to happen by copying
  	  computed the return value into a local temporary.  This also
  	  allows us to redirect multiple return statements through the
  	  same destination block; whether this is a net win or not really
  	  depends, I guess, but it does make generation of the switch in
  	  lower_try_finally_switch easier.  */
  
        switch (TREE_CODE (ret_expr))
  	{
  	case RESULT_DECL:
  	  if (!*return_value_p)
  	    *return_value_p = ret_expr;
  	  else
  	    gcc_assert (*return_value_p == ret_expr);
  	  q->cont_stmt = q->stmt;
  	  break;
  
  	case GIMPLE_MODIFY_STMT:
  	  {
  	    tree result = GIMPLE_STMT_OPERAND (ret_expr, 0);
  	    tree new, old = GIMPLE_STMT_OPERAND (ret_expr, 1);
  
  	    if (!*return_value_p)
  	      {
  		if (aggregate_value_p (TREE_TYPE (result),
  				      TREE_TYPE (current_function_decl)))
  		  /* If this function returns in memory, copy the argument
  		    into the return slot now.  Otherwise, we might need to
  		    worry about magic return semantics, so we need to use a
  		    temporary to hold the value until we're actually ready
  		    to return.  */
  		  new = result;
  		else
  		  new = create_tmp_var (TREE_TYPE (old), "rettmp");
  		*return_value_p = new;
  	      }
  	    else
  	      new = *return_value_p;
  
  	    x = build_gimple_modify_stmt (new, old);
  	    append_to_statement_list (x, &q->repl_stmt);
  
  	    if (new == result)
  	      x = result;
  	    else
  	      x = build_gimple_modify_stmt (result, new);
  	    q->cont_stmt = build1 (RETURN_EXPR, void_type_node, x);
  	  }
  
  	default:
  	  gcc_unreachable ();
  	}
      }
    else
      {
        /* If we don't return a value, all return statements are the same.  */
        q->cont_stmt = q->stmt;
      }
  
    if (mod)
      append_to_statement_list (mod, &q->repl_stmt);
  
    x = build1 (GOTO_EXPR, void_type_node, finlab);
    append_to_statement_list (x, &q->repl_stmt);
  }
  
  /* Similar, but easier, for GOTO_EXPR.  */
  
  static void
  do_goto_redirection (struct goto_queue_node *q, tree finlab, tree mod)
  {
    tree x;
  
    q->cont_stmt = q->stmt;
    if (mod)
      append_to_statement_list (mod, &q->repl_stmt);
  
    x = build1 (GOTO_EXPR, void_type_node, finlab);
    append_to_statement_list (x, &q->repl_stmt);
  }
  
  /* We want to transform
  	try { body; } catch { stuff; }
     to
  	body; goto over; lab: stuff; over:
  
     T is a TRY_FINALLY or TRY_CATCH node.  LAB is the label that
     should be placed before the second operand, or NULL.  OVER is
     an existing label that should be put at the exit, or NULL.  */
  
  static void
  frob_into_branch_around (tree *tp, tree lab, tree over)
  {
    tree x, op1;
  
    op1 = TREE_OPERAND (*tp, 1);
    *tp = TREE_OPERAND (*tp, 0);
  
    if (block_may_fallthru (*tp))
      {
        if (!over)
  	over = create_artificial_label ();
        x = build1 (GOTO_EXPR, void_type_node, over);
        append_to_statement_list (x, tp);
      }
  
    if (lab)
      {
        x = build1 (LABEL_EXPR, void_type_node, lab);
        append_to_statement_list (x, tp);
      }
  
    append_to_statement_list (op1, tp);
  
    if (over)
      {
        x = build1 (LABEL_EXPR, void_type_node, over);
        append_to_statement_list (x, tp);
      }
  }
  
  /* A subroutine of lower_try_finally.  Duplicate the tree rooted at T.
     Make sure to record all new labels found.  */
  
  static tree
  lower_try_finally_dup_block (tree t, struct leh_state *outer_state)
  {
    tree region = NULL;
  
    t = unsave_expr_now (t);
  
    if (outer_state->tf)
      region = outer_state->tf->try_finally_expr;
    collect_finally_tree (t, region);
  
    return t;
  }
  
  /* A subroutine of lower_try_finally.  Create a fallthru label for
     the given try_finally state.  The only tricky bit here is that
     we have to make sure to record the label in our outer context.  */
  
  static tree
  lower_try_finally_fallthru_label (struct leh_tf_state *tf)
  {
    tree label = tf->fallthru_label;
    if (!label)
      {
        label = create_artificial_label ();
        tf->fallthru_label = label;
        if (tf->outer->tf)
          record_in_finally_tree (label, tf->outer->tf->try_finally_expr);
      }
    return label;
  }
  
  /* A subroutine of lower_try_finally.  If lang_protect_cleanup_actions
     returns non-null, then the language requires that the exception path out
     of a try_finally be treated specially.  To wit: the code within the
     finally block may not itself throw an exception.  We have two choices here.
     First we can duplicate the finally block and wrap it in a must_not_throw
     region.  Second, we can generate code like
  
  	try {
  	  finally_block;
  	} catch {
  	  if (fintmp == eh_edge)
  	    protect_cleanup_actions;
  	}
  
     where "fintmp" is the temporary used in the switch statement generation
     alternative considered below.  For the nonce, we always choose the first
     option.
  
     THIS_STATE may be null if this is a try-cleanup, not a try-finally.  */
  
  static void
  honor_protect_cleanup_actions (struct leh_state *outer_state,
  			       struct leh_state *this_state,
  			       struct leh_tf_state *tf)
  {
    tree protect_cleanup_actions, finally, x;
    tree_stmt_iterator i;
    bool finally_may_fallthru;
  
    /* First check for nothing to do.  */
    if (lang_protect_cleanup_actions)
      protect_cleanup_actions = lang_protect_cleanup_actions ();
    else
      protect_cleanup_actions = NULL;
  
    finally = TREE_OPERAND (*tf->top_p, 1);
  
    /* If the EH case of the finally block can fall through, this may be a
       structure of the form
  	try {
  	  try {
  	    throw ...;
  	  } cleanup {
  	    try {
  	      throw ...;
  	    } catch (...) {
  	    }
  	  }
  	} catch (...) {
  	  yyy;
  	}
      E.g. with an inline destructor with an embedded try block.  In this
      case we must save the runtime EH data around the nested exception.
  
      This complication means that any time the previous runtime data might
      be used (via fallthru from the finally) we handle the eh case here,
      whether or not protect_cleanup_actions is active.  */
  
    finally_may_fallthru = block_may_fallthru (finally);
    if (!finally_may_fallthru && !protect_cleanup_actions)
      return;
  
    /* Duplicate the FINALLY block.  Only need to do this for try-finally,
       and not for cleanups.  */
    if (this_state)
      finally = lower_try_finally_dup_block (finally, outer_state);
  
    /* If this cleanup consists of a TRY_CATCH_EXPR with TRY_CATCH_IS_CLEANUP
       set, the handler of the TRY_CATCH_EXPR is another cleanup which ought
       to be in an enclosing scope, but needs to be implemented at this level
       to avoid a nesting violation (see wrap_temporary_cleanups in
       cp/decl.c).  Since it's logically at an outer level, we should call
       terminate before we get to it, so strip it away before adding the
       MUST_NOT_THROW filter.  */
    i = tsi_start (finally);
    x = tsi_stmt (i);
    if (protect_cleanup_actions
        && TREE_CODE (x) == TRY_CATCH_EXPR
        && TRY_CATCH_IS_CLEANUP (x))
      {
        tsi_link_before (&i, TREE_OPERAND (x, 0), TSI_SAME_STMT);
        tsi_delink (&i);
      }
  
    /* Resume execution after the exception.  Adding this now lets
       lower_eh_filter not add unnecessary gotos, as it is clear that
       we never fallthru from this copy of the finally block.  */
    if (finally_may_fallthru)
      {
        tree save_eptr, save_filt;
  
        save_eptr = create_tmp_var (ptr_type_node, "save_eptr");
        save_filt = create_tmp_var (integer_type_node, "save_filt");
  
        i = tsi_start (finally);
        x = build0 (EXC_PTR_EXPR, ptr_type_node);
        x = build_gimple_modify_stmt (save_eptr, x);
        tsi_link_before (&i, x, TSI_CONTINUE_LINKING);
  
        x = build0 (FILTER_EXPR, integer_type_node);
        x = build_gimple_modify_stmt (save_filt, x);
        tsi_link_before (&i, x, TSI_CONTINUE_LINKING);
  
        i = tsi_last (finally);
        x = build0 (EXC_PTR_EXPR, ptr_type_node);
        x = build_gimple_modify_stmt (x, save_eptr);
        tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  
        x = build0 (FILTER_EXPR, integer_type_node);
        x = build_gimple_modify_stmt (x, save_filt);
        tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  
        x = build_resx (get_eh_region_number (tf->region));
        tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
      }
  
    /* Wrap the block with protect_cleanup_actions as the action.  */
    if (protect_cleanup_actions)
      {
        x = build2 (EH_FILTER_EXPR, void_type_node, NULL, NULL);
        append_to_statement_list (protect_cleanup_actions, &EH_FILTER_FAILURE (x));
        EH_FILTER_MUST_NOT_THROW (x) = 1;
        finally = build2 (TRY_CATCH_EXPR, void_type_node, finally, x);
        lower_eh_filter (outer_state, &finally);
      }
    else
      lower_eh_constructs_1 (outer_state, &finally);
  
    /* Hook this up to the end of the existing try block.  If we
       previously fell through the end, we'll have to branch around.
       This means adding a new goto, and adding it to the queue.  */
  
    i = tsi_last (TREE_OPERAND (*tf->top_p, 0));
  
    if (tf->may_fallthru)
      {
        x = lower_try_finally_fallthru_label (tf);
        x = build1 (GOTO_EXPR, void_type_node, x);
        tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
  
        if (this_state)
          maybe_record_in_goto_queue (this_state, x);
  
        tf->may_fallthru = false;
      }
  
    x = build1 (LABEL_EXPR, void_type_node, tf->eh_label);
    tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
    tsi_link_after (&i, finally, TSI_CONTINUE_LINKING);
  
    /* Having now been handled, EH isn't to be considered with
       the rest of the outgoing edges.  */
    tf->may_throw = false;
  }
  
  /* A subroutine of lower_try_finally.  We have determined that there is
     no fallthru edge out of the finally block.  This means that there is
     no outgoing edge corresponding to any incoming edge.  Restructure the
     try_finally node for this special case.  */
  
  static void
  lower_try_finally_nofallthru (struct leh_state *state, struct leh_tf_state *tf)
  {
    tree x, finally, lab, return_val;
    struct goto_queue_node *q, *qe;
  
    if (tf->may_throw)
      lab = tf->eh_label;
    else
      lab = create_artificial_label ();
  
    finally = TREE_OPERAND (*tf->top_p, 1);
    *tf->top_p = TREE_OPERAND (*tf->top_p, 0);
  
    x = build1 (LABEL_EXPR, void_type_node, lab);
    append_to_statement_list (x, tf->top_p);
  
    return_val = NULL;
    q = tf->goto_queue;
    qe = q + tf->goto_queue_active;
    for (; q < qe; ++q)
      if (q->index < 0)
        do_return_redirection (q, lab, NULL, &return_val);
      else
        do_goto_redirection (q, lab, NULL);
  
    replace_goto_queue (tf);
  
    lower_eh_constructs_1 (state, &finally);
    append_to_statement_list (finally, tf->top_p);
  }
  
  /* A subroutine of lower_try_finally.  We have determined that there is
     exactly one destination of the finally block.  Restructure the
     try_finally node for this special case.  */
  
  static void
  lower_try_finally_onedest (struct leh_state *state, struct leh_tf_state *tf)
  {
    struct goto_queue_node *q, *qe;
    tree x, finally, finally_label;
  
    finally = TREE_OPERAND (*tf->top_p, 1);
    *tf->top_p = TREE_OPERAND (*tf->top_p, 0);
  
    lower_eh_constructs_1 (state, &finally);
  
    if (tf->may_throw)
      {
        /* Only reachable via the exception edge.  Add the given label to
           the head of the FINALLY block.  Append a RESX at the end.  */
  
        x = build1 (LABEL_EXPR, void_type_node, tf->eh_label);
        append_to_statement_list (x, tf->top_p);
  
        append_to_statement_list (finally, tf->top_p);
  
        x = build_resx (get_eh_region_number (tf->region));
  
        append_to_statement_list (x, tf->top_p);
  
        return;
      }
  
    if (tf->may_fallthru)
      {
        /* Only reachable via the fallthru edge.  Do nothing but let
  	 the two blocks run together; we'll fall out the bottom.  */
        append_to_statement_list (finally, tf->top_p);
        return;
      }
  
    finally_label = create_artificial_label ();
    x = build1 (LABEL_EXPR, void_type_node, finally_label);
    append_to_statement_list (x, tf->top_p);
  
    append_to_statement_list (finally, tf->top_p);
  
    q = tf->goto_queue;
    qe = q + tf->goto_queue_active;
  
    if (tf->may_return)
      {
        /* Reachable by return expressions only.  Redirect them.  */
        tree return_val = NULL;
        for (; q < qe; ++q)
  	do_return_redirection (q, finally_label, NULL, &return_val);
        replace_goto_queue (tf);
      }
    else
      {
        /* Reachable by goto expressions only.  Redirect them.  */
        for (; q < qe; ++q)
  	do_goto_redirection (q, finally_label, NULL);
        replace_goto_queue (tf);
  
        if (VEC_index (tree, tf->dest_array, 0) == tf->fallthru_label)
  	{
  	  /* Reachable by goto to fallthru label only.  Redirect it
  	     to the new label (already created, sadly), and do not
  	     emit the final branch out, or the fallthru label.  */
  	  tf->fallthru_label = NULL;
  	  return;
  	}
      }
  
    /* Reset the locus of the goto since we're moving 
       goto to a different block which might be on a different line. */
    SET_EXPR_LOCUS (tf->goto_queue[0].cont_stmt, NULL);
    append_to_statement_list (tf->goto_queue[0].cont_stmt, tf->top_p);
    maybe_record_in_goto_queue (state, tf->goto_queue[0].cont_stmt);
  }
  
  /* A subroutine of lower_try_finally.  There are multiple edges incoming
     and outgoing from the finally block.  Implement this by duplicating the
     finally block for every destination.  */
  
  static void
  lower_try_finally_copy (struct leh_state *state, struct leh_tf_state *tf)
  {
    tree finally, new_stmt;
    tree x;
  
    finally = TREE_OPERAND (*tf->top_p, 1);
    *tf->top_p = TREE_OPERAND (*tf->top_p, 0);
  
    new_stmt = NULL_TREE;
  
    if (tf->may_fallthru)
      {
        x = lower_try_finally_dup_block (finally, state);
        lower_eh_constructs_1 (state, &x);
        append_to_statement_list (x, &new_stmt);
  
        x = lower_try_finally_fallthru_label (tf);
        x = build1 (GOTO_EXPR, void_type_node, x);
        append_to_statement_list (x, &new_stmt);
      }
  
    if (tf->may_throw)
      {
        x = build1 (LABEL_EXPR, void_type_node, tf->eh_label);
        append_to_statement_list (x, &new_stmt);
  
        x = lower_try_finally_dup_block (finally, state);
        lower_eh_constructs_1 (state, &x);
        append_to_statement_list (x, &new_stmt);
  
        x = build_resx (get_eh_region_number (tf->region));
        append_to_statement_list (x, &new_stmt);
      }
  
    if (tf->goto_queue)
      {
        struct goto_queue_node *q, *qe;
        tree return_val = NULL;
        int return_index, index;
        struct labels_s
        {
  	struct goto_queue_node *q;
  	tree label;
        } *labels;
  
        return_index = VEC_length (tree, tf->dest_array);
        labels = XCNEWVEC (struct labels_s, return_index + 1);
  
        q = tf->goto_queue;
        qe = q + tf->goto_queue_active;
        for (; q < qe; q++)
  	{
  	  index = q->index < 0 ? return_index : q->index;
  
  	  if (!labels[index].q)
  	    labels[index].q = q;
  	}
  
        for (index = 0; index < return_index + 1; index++)
  	{
  	  tree lab;
  
  	  q = labels[index].q;
  	  if (! q)
  	    continue;
  
  	  lab = labels[index].label = create_artificial_label ();
  
  	  if (index == return_index)
  	    do_return_redirection (q, lab, NULL, &return_val);
  	  else
  	    do_goto_redirection (q, lab, NULL);
  
  	  x = build1 (LABEL_EXPR, void_type_node, lab);
  	  append_to_statement_list (x, &new_stmt);
  
  	  x = lower_try_finally_dup_block (finally, state);
  	  lower_eh_constructs_1 (state, &x);
  	  append_to_statement_list (x, &new_stmt);
  
  	  append_to_statement_list (q->cont_stmt, &new_stmt);
  	  maybe_record_in_goto_queue (state, q->cont_stmt);
  	}
  
        for (q = tf->goto_queue; q < qe; q++)
  	{
  	  tree lab;
  
  	  index = q->index < 0 ? return_index : q->index;
  
  	  if (labels[index].q == q)
  	    continue;
  
  	  lab = labels[index].label;
  
  	  if (index == return_index)
  	    do_return_redirection (q, lab, NULL, &return_val);
  	  else
  	    do_goto_redirection (q, lab, NULL);
  	}
  	
        replace_goto_queue (tf);
        free (labels);
      }
  
    /* Need to link new stmts after running replace_goto_queue due
       to not wanting to process the same goto stmts twice.  */
    append_to_statement_list (new_stmt, tf->top_p);
  }
  
  /* A subroutine of lower_try_finally.  There are multiple edges incoming
     and outgoing from the finally block.  Implement this by instrumenting
     each incoming edge and creating a switch statement at the end of the
     finally block that branches to the appropriate destination.  */
  
  static void
  lower_try_finally_switch (struct leh_state *state, struct leh_tf_state *tf)
  {
    struct goto_queue_node *q, *qe;
    tree return_val = NULL;
    tree finally, finally_tmp, finally_label;
    int return_index, eh_index, fallthru_index;
    int nlabels, ndests, j, last_case_index;
    tree case_label_vec, switch_stmt, last_case, switch_body;
    tree x;
  
    /* Mash the TRY block to the head of the chain.  */
    finally = TREE_OPERAND (*tf->top_p, 1);
    *tf->top_p = TREE_OPERAND (*tf->top_p, 0);
  
    /* Lower the finally block itself.  */
    lower_eh_constructs_1 (state, &finally);
  
    /* Prepare for switch statement generation.  */
    nlabels = VEC_length (tree, tf->dest_array);
    return_index = nlabels;
    eh_index = return_index + tf->may_return;
    fallthru_index = eh_index + tf->may_throw;
    ndests = fallthru_index + tf->may_fallthru;
  
    finally_tmp = create_tmp_var (integer_type_node, "finally_tmp");
    finally_label = create_artificial_label ();
  
    case_label_vec = make_tree_vec (ndests);
    switch_stmt = build3 (SWITCH_EXPR, integer_type_node, finally_tmp,
  		        NULL_TREE, case_label_vec);
    switch_body = NULL;
    last_case = NULL;
    last_case_index = 0;
  
    /* Begin inserting code for getting to the finally block.  Things
       are done in this order to correspond to the sequence the code is
       layed out.  */
  
    if (tf->may_fallthru)
      {
        x = build_gimple_modify_stmt (finally_tmp,
  				    build_int_cst (integer_type_node,
  						   fallthru_index));
        append_to_statement_list (x, tf->top_p);
  
        if (tf->may_throw)
  	{
  	  x = build1 (GOTO_EXPR, void_type_node, finally_label);
  	  append_to_statement_list (x, tf->top_p);
  	}
  
  
        last_case = build3 (CASE_LABEL_EXPR, void_type_node,
  			  build_int_cst (NULL_TREE, fallthru_index), NULL,
  			  create_artificial_label ());
        TREE_VEC_ELT (case_label_vec, last_case_index) = last_case;
        last_case_index++;
  
        x = build1 (LABEL_EXPR, void_type_node, CASE_LABEL (last_case));
        append_to_statement_list (x, &switch_body);
  
        x = lower_try_finally_fallthru_label (tf);
        x = build1 (GOTO_EXPR, void_type_node, x);
        append_to_statement_list (x, &switch_body);
      }
  
    if (tf->may_throw)
      {
        x = build1 (LABEL_EXPR, void_type_node, tf->eh_label);
        append_to_statement_list (x, tf->top_p);
  
        x = build_gimple_modify_stmt (finally_tmp,
  				    build_int_cst (integer_type_node,
  						   eh_index));
        append_to_statement_list (x, tf->top_p);
  
        last_case = build3 (CASE_LABEL_EXPR, void_type_node,
  			  build_int_cst (NULL_TREE, eh_index), NULL,
  			  create_artificial_label ());
        TREE_VEC_ELT (case_label_vec, last_case_index) = last_case;
        last_case_index++;
  
        x = build1 (LABEL_EXPR, void_type_node, CASE_LABEL (last_case));
        append_to_statement_list (x, &switch_body);
        x = build_resx (get_eh_region_number (tf->region));
        append_to_statement_list (x, &switch_body);
      }
  
    x = build1 (LABEL_EXPR, void_type_node, finally_label);
    append_to_statement_list (x, tf->top_p);
  
    append_to_statement_list (finally, tf->top_p);
  
    /* Redirect each incoming goto edge.  */
    q = tf->goto_queue;
    qe = q + tf->goto_queue_active;
    j = last_case_index + tf->may_return;
    for (; q < qe; ++q)
      {
        tree mod;
        int switch_id, case_index;
  
        if (q->index < 0)
  	{
  	  mod = build_gimple_modify_stmt (finally_tmp,
  					  build_int_cst (integer_type_node,
  							 return_index));
  	  do_return_redirection (q, finally_label, mod, &return_val);
  	  switch_id = return_index;
  	}
        else
  	{
  	  mod = build_gimple_modify_stmt (finally_tmp,
  					  build_int_cst (integer_type_node,
  							 q->index));
  	  do_goto_redirection (q, finally_label, mod);
  	  switch_id = q->index;
  	}
  
        case_index = j + q->index;
        if (!TREE_VEC_ELT (case_label_vec, case_index))
  	TREE_VEC_ELT (case_label_vec, case_index)
  	  = build3 (CASE_LABEL_EXPR, void_type_node,
  		    build_int_cst (NULL_TREE, switch_id), NULL,
  		    /* We store the cont_stmt in the
  		       CASE_LABEL, so that we can recover it
  		       in the loop below.  We don't create
  		       the new label while walking the
  		       goto_queue because pointers don't
  		       offer a stable order.  */
  		    q->cont_stmt);
      }
    for (j = last_case_index; j < last_case_index + nlabels; j++)
      {
        tree label;
        tree cont_stmt;
  
        last_case = TREE_VEC_ELT (case_label_vec, j);
  
        gcc_assert (last_case);
  
        cont_stmt = CASE_LABEL (last_case);
  
        label = create_artificial_label ();
        CASE_LABEL (last_case) = label;
  
        x = build1 (LABEL_EXPR, void_type_node, label);
        append_to_statement_list (x, &switch_body);
        append_to_statement_list (cont_stmt, &switch_body);
        maybe_record_in_goto_queue (state, cont_stmt);
      }
    replace_goto_queue (tf);
  
    /* Make sure that the last case is the default label, as one is required.
       Then sort the labels, which is also required in GIMPLE.  */
    CASE_LOW (last_case) = NULL;
    sort_case_labels (case_label_vec);
  
    /* Need to link switch_stmt after running replace_goto_queue due
       to not wanting to process the same goto stmts twice.  */
    append_to_statement_list (switch_stmt, tf->top_p);
    append_to_statement_list (switch_body, tf->top_p);
  }
  
  /* Decide whether or not we are going to duplicate the finally block.
     There are several considerations.
  
     First, if this is Java, then the finally block contains code
     written by the user.  It has line numbers associated with it,
     so duplicating the block means it's difficult to set a breakpoint.
     Since controlling code generation via -g is verboten, we simply
     never duplicate code without optimization.
  
     Second, we'd like to prevent egregious code growth.  One way to
     do this is to estimate the size of the finally block, multiply
     that by the number of copies we'd need to make, and compare against
     the estimate of the size of the switch machinery we'd have to add.  */
  
  static bool
  decide_copy_try_finally (int ndests, tree finally)
  {
    int f_estimate, sw_estimate;
  
    if (!optimize)
      return false;
  
    /* Finally estimate N times, plus N gotos.  */
    f_estimate = estimate_num_insns (finally, &eni_size_weights);
    f_estimate = (f_estimate + 1) * ndests;
  
    /* Switch statement (cost 10), N variable assignments, N gotos.  */
    sw_estimate = 10 + 2 * ndests;
  
    /* Optimize for size clearly wants our best guess.  */
    if (optimize_size)
      return f_estimate < sw_estimate;
  
    /* ??? These numbers are completely made up so far.  */
    if (optimize > 1)
      return f_estimate < 100 || f_estimate < sw_estimate * 2;
    else
      return f_estimate < 40 || f_estimate * 2 < sw_estimate * 3;
  }
  
  /* A subroutine of lower_eh_constructs_1.  Lower a TRY_FINALLY_EXPR nodes
     to a sequence of labels and blocks, plus the exception region trees
     that record all the magic.  This is complicated by the need to
     arrange for the FINALLY block to be executed on all exits.  */
  
  static void
  lower_try_finally (struct leh_state *state, tree *tp)
  {
    struct leh_tf_state this_tf;
    struct leh_state this_state;
    int ndests;
  
    /* Process the try block.  */
  
    memset (&this_tf, 0, sizeof (this_tf));
    this_tf.try_finally_expr = *tp;
    this_tf.top_p = tp;
    this_tf.outer = state;
    if (using_eh_for_cleanups_p)
      this_tf.region
        = gen_eh_region_cleanup (state->cur_region, state->prev_try);
    else
      this_tf.region = NULL;
  
    this_state.cur_region = this_tf.region;
    this_state.prev_try = state->prev_try;
    this_state.tf = &this_tf;
  
    lower_eh_constructs_1 (&this_state, &TREE_OPERAND (*tp, 0));
  
    /* Determine if the try block is escaped through the bottom.  */
    this_tf.may_fallthru = block_may_fallthru (TREE_OPERAND (*tp, 0));
  
    /* Determine if any exceptions are possible within the try block.  */
    if (using_eh_for_cleanups_p)
      this_tf.may_throw = get_eh_region_may_contain_throw (this_tf.region);
    if (this_tf.may_throw)
      {
        this_tf.eh_label = create_artificial_label ();
        set_eh_region_tree_label (this_tf.region, this_tf.eh_label);
        honor_protect_cleanup_actions (state, &this_state, &this_tf);
      }
  
    /* Determine how many edges (still) reach the finally block.  Or rather,
       how many destinations are reached by the finally block.  Use this to
       determine how we process the finally block itself.  */
  
    ndests = VEC_length (tree, this_tf.dest_array);
    ndests += this_tf.may_fallthru;
    ndests += this_tf.may_return;
    ndests += this_tf.may_throw;
  
    /* If the FINALLY block is not reachable, dike it out.  */
    if (ndests == 0)
      *tp = TREE_OPERAND (*tp, 0);
  
    /* If the finally block doesn't fall through, then any destination
       we might try to impose there isn't reached either.  There may be
       some minor amount of cleanup and redirection still needed.  */
    else if (!block_may_fallthru (TREE_OPERAND (*tp, 1)))
      lower_try_finally_nofallthru (state, &this_tf);
  
    /* We can easily special-case redirection to a single destination.  */
    else if (ndests == 1)
      lower_try_finally_onedest (state, &this_tf);
  
    else if (decide_copy_try_finally (ndests, TREE_OPERAND (*tp, 1)))
      lower_try_finally_copy (state, &this_tf);
    else
      lower_try_finally_switch (state, &this_tf);
  
    /* If someone requested we add a label at the end of the transformed
       block, do so.  */
    if (this_tf.fallthru_label)
      {
        tree x = build1 (LABEL_EXPR, void_type_node, this_tf.fallthru_label);
        append_to_statement_list (x, tp);
      }
  
    VEC_free (tree, heap, this_tf.dest_array);
    if (this_tf.goto_queue)
      free (this_tf.goto_queue);
    if (this_tf.goto_queue_map)
      pointer_map_destroy (this_tf.goto_queue_map);
  }
  
  /* A subroutine of lower_eh_constructs_1.  Lower a TRY_CATCH_EXPR with a
     list of CATCH_EXPR nodes to a sequence of labels and blocks, plus the
     exception region trees that record all the magic.  */
  
  static void
  lower_catch (struct leh_state *state, tree *tp)
  {
    struct eh_region *try_region;
    struct leh_state this_state;
    tree_stmt_iterator i;
    tree out_label;
  
    try_region = gen_eh_region_try (state->cur_region);
    this_state.cur_region = try_region;
    this_state.prev_try = try_region;
    this_state.tf = state->tf;
  
    lower_eh_constructs_1 (&this_state, &TREE_OPERAND (*tp, 0));
  
    if (!get_eh_region_may_contain_throw (try_region))
      {
        *tp = TREE_OPERAND (*tp, 0);
        return;
      }
  
    out_label = NULL;
    for (i = tsi_start (TREE_OPERAND (*tp, 1)); !tsi_end_p (i); )
      {
        struct eh_region *catch_region;
        tree catch, x, eh_label;
  
        catch = tsi_stmt (i);
        catch_region = gen_eh_region_catch (try_region, CATCH_TYPES (catch));
  
        this_state.cur_region = catch_region;
        this_state.prev_try = state->prev_try;
        lower_eh_constructs_1 (&this_state, &CATCH_BODY (catch));
  
        eh_label = create_artificial_label ();
        set_eh_region_tree_label (catch_region, eh_label);
  
        x = build1 (LABEL_EXPR, void_type_node, eh_label);
        tsi_link_before (&i, x, TSI_SAME_STMT);
  
        if (block_may_fallthru (CATCH_BODY (catch)))
  	{
  	  if (!out_label)
  	    out_label = create_artificial_label ();
  
  	  x = build1 (GOTO_EXPR, void_type_node, out_label);
  	  append_to_statement_list (x, &CATCH_BODY (catch));
  	}
  
        tsi_link_before (&i, CATCH_BODY (catch), TSI_SAME_STMT);
        tsi_delink (&i);
      }
  
    frob_into_branch_around (tp, NULL, out_label);
  }
  
  /* A subroutine of lower_eh_constructs_1.  Lower a TRY_CATCH_EXPR with a
     EH_FILTER_EXPR to a sequence of labels and blocks, plus the exception
     region trees that record all the magic.  */
  
  static void
  lower_eh_filter (struct leh_state *state, tree *tp)
  {
    struct leh_state this_state;
    struct eh_region *this_region;
    tree inner = expr_first (TREE_OPERAND (*tp, 1));
    tree eh_label;
  
    if (EH_FILTER_MUST_NOT_THROW (inner))
      this_region = gen_eh_region_must_not_throw (state->cur_region);
    else
      this_region = gen_eh_region_allowed (state->cur_region,
  					 EH_FILTER_TYPES (inner));
    this_state = *state;
    this_state.cur_region = this_region;
    /* For must not throw regions any cleanup regions inside it
       can't reach outer catch regions.  */
    if (EH_FILTER_MUST_NOT_THROW (inner))
      this_state.prev_try = NULL;
  
    lower_eh_constructs_1 (&this_state, &TREE_OPERAND (*tp, 0));
  
    if (!get_eh_region_may_contain_throw (this_region))
      {
        *tp = TREE_OPERAND (*tp, 0);
        return;
      }
  
    lower_eh_constructs_1 (state, &EH_FILTER_FAILURE (inner));
    TREE_OPERAND (*tp, 1) = EH_FILTER_FAILURE (inner);
  
    eh_label = create_artificial_label ();
    set_eh_region_tree_label (this_region, eh_label);
  
    frob_into_branch_around (tp, eh_label, NULL);
  }
  
  /* Implement a cleanup expression.  This is similar to try-finally,
     except that we only execute the cleanup block for exception edges.  */
  
  static void
  lower_cleanup (struct leh_state *state, tree *tp)
  {
    struct leh_state this_state;
    struct eh_region *this_region;
    struct leh_tf_state fake_tf;
  
    /* If not using eh, then exception-only cleanups are no-ops.  */
    if (!flag_exceptions)
      {
        *tp = TREE_OPERAND (*tp, 0);
        lower_eh_constructs_1 (state, tp);
        return;
      }
  
    this_region = gen_eh_region_cleanup (state->cur_region, state->prev_try);
    this_state = *state;
    this_state.cur_region = this_region;
  
    lower_eh_constructs_1 (&this_state, &TREE_OPERAND (*tp, 0));
  
    if (!get_eh_region_may_contain_throw (this_region))
      {
        *tp = TREE_OPERAND (*tp, 0);
        return;
      }
  
    /* Build enough of a try-finally state so that we can reuse
       honor_protect_cleanup_actions.  */
    memset (&fake_tf, 0, sizeof (fake_tf));
    fake_tf.top_p = tp;
    fake_tf.outer = state;
    fake_tf.region = this_region;
    fake_tf.may_fallthru = block_may_fallthru (TREE_OPERAND (*tp, 0));
    fake_tf.may_throw = true;
  
    fake_tf.eh_label = create_artificial_label ();
    set_eh_region_tree_label (this_region, fake_tf.eh_label);
  
    honor_protect_cleanup_actions (state, NULL, &fake_tf);
  
    if (fake_tf.may_throw)
      {
        /* In this case honor_protect_cleanup_actions had nothing to do,
  	 and we should process this normally.  */
        lower_eh_constructs_1 (state, &TREE_OPERAND (*tp, 1));
        frob_into_branch_around (tp, fake_tf.eh_label, fake_tf.fallthru_label);
      }
    else
      {
        /* In this case honor_protect_cleanup_actions did nearly all of
  	 the work.  All we have left is to append the fallthru_label.  */
  
        *tp = TREE_OPERAND (*tp, 0);
        if (fake_tf.fallthru_label)
  	{
  	  tree x = build1 (LABEL_EXPR, void_type_node, fake_tf.fallthru_label);
  	  append_to_statement_list (x, tp);
  	}
      }
  }
  
  /* Main loop for lowering eh constructs.  */
  
  static void
  lower_eh_constructs_1 (struct leh_state *state, tree *tp)
  {
    tree_stmt_iterator i;
    tree t = *tp;
  
    switch (TREE_CODE (t))
      {
      case COND_EXPR:
        lower_eh_constructs_1 (state, &COND_EXPR_THEN (t));
        lower_eh_constructs_1 (state, &COND_EXPR_ELSE (t));
        break;
  
      case CALL_EXPR:
        /* Look for things that can throw exceptions, and record them.  */
        if (state->cur_region && tree_could_throw_p (t))
  	{
  	  record_stmt_eh_region (state->cur_region, t);
  	  note_eh_region_may_contain_throw (state->cur_region);
  	}
        break;
  
      case GIMPLE_MODIFY_STMT:
        /* Look for things that can throw exceptions, and record them.  */
        if (state->cur_region && tree_could_throw_p (t))
  	{
  	  record_stmt_eh_region (state->cur_region, t);
  	  note_eh_region_may_contain_throw (state->cur_region);
  	}
        break;
  
      case GOTO_EXPR:
      case RETURN_EXPR:
        maybe_record_in_goto_queue (state, t);
        break;
      case SWITCH_EXPR:
        verify_norecord_switch_expr (state, t);
        break;
  
      case TRY_FINALLY_EXPR:
        lower_try_finally (state, tp);
        break;
  
      case TRY_CATCH_EXPR:
        i = tsi_start (TREE_OPERAND (t, 1));
        switch (TREE_CODE (tsi_stmt (i)))
  	{
  	case CATCH_EXPR:
  	  lower_catch (state, tp);
  	  break;
  	case EH_FILTER_EXPR:
  	  lower_eh_filter (state, tp);
  	  break;
  	default:
  	  lower_cleanup (state, tp);
  	  break;
  	}
        break;
  
      case STATEMENT_LIST:
        for (i = tsi_start (t); !tsi_end_p (i); )
  	{
  	  lower_eh_constructs_1 (state, tsi_stmt_ptr (i));
  	  t = tsi_stmt (i);
  	  if (TREE_CODE (t) == STATEMENT_LIST)
  	    {
  	      tsi_link_before (&i, t, TSI_SAME_STMT);
  	      tsi_delink (&i);
  	    }
  	  else
  	    tsi_next (&i);
  	}
        break;
  
      default:
        /* A type, a decl, or some kind of statement that we're not
  	 interested in.  Don't walk them.  */
        break;
      }
  }
  
  static unsigned int
  lower_eh_constructs (void)
  {
    struct leh_state null_state;
    tree *tp = &DECL_SAVED_TREE (current_function_decl);
  
    finally_tree = htab_create (31, struct_ptr_hash, struct_ptr_eq, free);
  
    collect_finally_tree (*tp, NULL);
  
    memset (&null_state, 0, sizeof (null_state));
    lower_eh_constructs_1 (&null_state, tp);
  
    htab_delete (finally_tree);
  
    collect_eh_region_array ();
    return 0;
  }
  
  struct tree_opt_pass pass_lower_eh =
  {
    "eh",					/* name */
    NULL,					/* gate */
    lower_eh_constructs,			/* execute */
    NULL,					/* sub */
    NULL,					/* next */
    0,					/* static_pass_number */
    TV_TREE_EH,				/* tv_id */
    PROP_gimple_lcf,			/* properties_required */
    PROP_gimple_leh,			/* properties_provided */
    0,					/* properties_destroyed */
    0,					/* todo_flags_start */
    TODO_dump_func,			/* todo_flags_finish */
    0					/* letter */
  };
  
  
  /* Construct EH edges for STMT.  */
  
  static void
  make_eh_edge (struct eh_region *region, void *data)
  {
    tree stmt, lab;
    basic_block src, dst;
  
    stmt = (tree) data;
    lab = get_eh_region_tree_label (region);
  
    src = bb_for_stmt (stmt);
    dst = label_to_block (lab);
  
    make_edge (src, dst, EDGE_ABNORMAL | EDGE_EH);
  }
  
  void
  make_eh_edges (tree stmt)
  {
    int region_nr;
    bool is_resx;
  
    if (TREE_CODE (stmt) == RESX_EXPR)
      {
        region_nr = TREE_INT_CST_LOW (TREE_OPERAND (stmt, 0));
        is_resx = true;
      }
    else
      {
        region_nr = lookup_stmt_eh_region (stmt);
        if (region_nr < 0)
  	return;
        is_resx = false;
      }
  
    foreach_reachable_handler (region_nr, is_resx, make_eh_edge, stmt);
  }
  
  static bool mark_eh_edge_found_error;
  
  /* Mark edge make_eh_edge would create for given region by setting it aux
     field, output error if something goes wrong.  */
  static void
  mark_eh_edge (struct eh_region *region, void *data)
  {
    tree stmt, lab;
    basic_block src, dst;
    edge e;
  
    stmt = (tree) data;
    lab = get_eh_region_tree_label (region);
  
    src = bb_for_stmt (stmt);
    dst = label_to_block (lab);
  
    e = find_edge (src, dst);
    if (!e)
      {
        error ("EH edge %i->%i is missing", src->index, dst->index);
        mark_eh_edge_found_error = true;
      }
    else if (!(e->flags & EDGE_EH))
      {
        error ("EH edge %i->%i miss EH flag", src->index, dst->index);
        mark_eh_edge_found_error = true;
      }
    else if (e->aux)
      {
        /* ??? might not be mistake.  */
        error ("EH edge %i->%i has duplicated regions", src->index, dst->index);
        mark_eh_edge_found_error = true;
      }
    else
      e->aux = (void *)1;
  }
  
  /* Verify that BB containing stmt as last stmt has precisely the edges
     make_eh_edges would create.  */
  bool
  verify_eh_edges (tree stmt)
  {
    int region_nr;
    bool is_resx;
    basic_block bb = bb_for_stmt (stmt);
    edge_iterator ei;
    edge e;
  
    FOR_EACH_EDGE (e, ei, bb->succs)
      gcc_assert (!e->aux);
    mark_eh_edge_found_error = false;
    if (TREE_CODE (stmt) == RESX_EXPR)
      {
        region_nr = TREE_INT_CST_LOW (TREE_OPERAND (stmt, 0));
        is_resx = true;
      }
    else
      {
        region_nr = lookup_stmt_eh_region (stmt);
        if (region_nr < 0)
  	{
  	  FOR_EACH_EDGE (e, ei, bb->succs)
  	    if (e->flags & EDGE_EH)
  	      {
  		error ("BB %i can not throw but has EH edges", bb->index);
  		return true;
  	      }
  	   return false;
  	}
        if (!tree_could_throw_p (stmt))
  	{
  	  error ("BB %i last statement has incorrectly set region", bb->index);
  	  return true;
  	}
        is_resx = false;
      }
  
    foreach_reachable_handler (region_nr, is_resx, mark_eh_edge, stmt);
    FOR_EACH_EDGE (e, ei, bb->succs)
      {
        if ((e->flags & EDGE_EH) && !e->aux)
  	{
  	  error ("unnecessary EH edge %i->%i", bb->index, e->dest->index);
  	  mark_eh_edge_found_error = true;
  	  return true;
  	}
        e->aux = NULL;
      }
    return mark_eh_edge_found_error;
  }
  
  
  /* Return true if the expr can trap, as in dereferencing an invalid pointer
     location or floating point arithmetic.  C.f. the rtl version, may_trap_p.
     This routine expects only GIMPLE lhs or rhs input.  */
  
  bool
  tree_could_trap_p (tree expr)
  {
    enum tree_code code = TREE_CODE (expr);
    bool honor_nans = false;
    bool honor_snans = false;
    bool fp_operation = false;
    bool honor_trapv = false;
    tree t, base;
  
    if (TREE_CODE_CLASS (code) == tcc_comparison
        || TREE_CODE_CLASS (code) == tcc_unary
        || TREE_CODE_CLASS (code) == tcc_binary)
      {
        t = TREE_TYPE (expr);
        fp_operation = FLOAT_TYPE_P (t);
        if (fp_operation)
  	{
  	  honor_nans = flag_trapping_math && !flag_finite_math_only;
  	  honor_snans = flag_signaling_nans != 0;
  	}
        else if (INTEGRAL_TYPE_P (t) && TYPE_OVERFLOW_TRAPS (t))
  	honor_trapv = true;
      }
  
   restart:
    switch (code)
      {
      case TARGET_MEM_REF:
        /* For TARGET_MEM_REFs use the information based on the original
  	 reference.  */
        expr = TMR_ORIGINAL (expr);
        code = TREE_CODE (expr);
        goto restart;
  
      case COMPONENT_REF:
      case REALPART_EXPR:
      case IMAGPART_EXPR:
      case BIT_FIELD_REF:
      case VIEW_CONVERT_EXPR:
      case WITH_SIZE_EXPR:
        expr = TREE_OPERAND (expr, 0);
        code = TREE_CODE (expr);
        goto restart;
  
      case ARRAY_RANGE_REF:
        base = TREE_OPERAND (expr, 0);
        if (tree_could_trap_p (base))
  	return true;
  
        if (TREE_THIS_NOTRAP (expr))
  	return false;
  
        return !range_in_array_bounds_p (expr);
  
      case ARRAY_REF:
        base = TREE_OPERAND (expr, 0);
        if (tree_could_trap_p (base))
  	return true;
  
        if (TREE_THIS_NOTRAP (expr))
  	return false;
  
        return !in_array_bounds_p (expr);
  
      case INDIRECT_REF:
      case ALIGN_INDIRECT_REF:
      case MISALIGNED_INDIRECT_REF:
        return !TREE_THIS_NOTRAP (expr);
  
      case ASM_EXPR:
        return TREE_THIS_VOLATILE (expr);
  
      case TRUNC_DIV_EXPR:
      case CEIL_DIV_EXPR:
      case FLOOR_DIV_EXPR:
      case ROUND_DIV_EXPR:
      case EXACT_DIV_EXPR:
      case CEIL_MOD_EXPR:
      case FLOOR_MOD_EXPR:
      case ROUND_MOD_EXPR:
      case TRUNC_MOD_EXPR:
      case RDIV_EXPR:
        if (honor_snans || honor_trapv)
  	return true;
        if (fp_operation)
  	return flag_trapping_math;
        t = TREE_OPERAND (expr, 1);
        if (!TREE_CONSTANT (t) || integer_zerop (t))
          return true;
        return false;
  
      case LT_EXPR:
      case LE_EXPR:
      case GT_EXPR:
      case GE_EXPR:
      case LTGT_EXPR:
        /* Some floating point comparisons may trap.  */
        return honor_nans;
  
      case EQ_EXPR:
      case NE_EXPR:
      case UNORDERED_EXPR:
      case ORDERED_EXPR:
      case UNLT_EXPR:
      case UNLE_EXPR:
      case UNGT_EXPR:
      case UNGE_EXPR:
      case UNEQ_EXPR:
        return honor_snans;
  
      case CONVERT_EXPR:
      case FIX_TRUNC_EXPR:
        /* Conversion of floating point might trap.  */
        return honor_nans;
  
      case NEGATE_EXPR:
      case ABS_EXPR:
      case CONJ_EXPR:
        /* These operations don't trap with floating point.  */
        if (honor_trapv)
  	return true;
        return false;
  
      case PLUS_EXPR:
      case MINUS_EXPR:
      case MULT_EXPR:
        /* Any floating arithmetic may trap.  */
        if (fp_operation && flag_trapping_math)
  	return true;
        if (honor_trapv)
  	return true;
        return false;
  
      case CALL_EXPR:
        t = get_callee_fndecl (expr);
        /* Assume that calls to weak functions may trap.  */
        if (!t || !DECL_P (t) || DECL_WEAK (t))
  	return true;
        return false;
  
      default:
        /* Any floating arithmetic may trap.  */
        if (fp_operation && flag_trapping_math)
  	return true;
        return false;
      }
  }
  
  bool
  tree_could_throw_p (tree t)
  {
    if (!flag_exceptions)
      return false;
    if (TREE_CODE (t) == GIMPLE_MODIFY_STMT)
      {
        if (flag_non_call_exceptions
  	  && tree_could_trap_p (GIMPLE_STMT_OPERAND (t, 0)))
  	return true;
        t = GIMPLE_STMT_OPERAND (t, 1);
      }
  
    if (TREE_CODE (t) == WITH_SIZE_EXPR)
      t = TREE_OPERAND (t, 0);
    if (TREE_CODE (t) == CALL_EXPR)
      return (call_expr_flags (t) & ECF_NOTHROW) == 0;
    if (flag_non_call_exceptions)
      return tree_could_trap_p (t);
    return false;
  }
  
  bool
  tree_can_throw_internal (const_tree stmt)
  {
    int region_nr;
    bool is_resx = false;
  
    if (TREE_CODE (stmt) == RESX_EXPR)
      region_nr = TREE_INT_CST_LOW (TREE_OPERAND (stmt, 0)), is_resx = true;
    else
      region_nr = lookup_stmt_eh_region (stmt);
    if (region_nr < 0)
      return false;
    return can_throw_internal_1 (region_nr, is_resx);
  }
  
  bool
  tree_can_throw_external (tree stmt)
  {
    int region_nr;
    bool is_resx = false;
  
    if (TREE_CODE (stmt) == RESX_EXPR)
      region_nr = TREE_INT_CST_LOW (TREE_OPERAND (stmt, 0)), is_resx = true;
    else
      region_nr = lookup_stmt_eh_region (stmt);
    if (region_nr < 0)
      return tree_could_throw_p (stmt);
    else
      return can_throw_external_1 (region_nr, is_resx);
  }
  
  /* Given a statement OLD_STMT and a new statement NEW_STMT that has replaced
     OLD_STMT in the function, remove OLD_STMT from the EH table and put NEW_STMT
     in the table if it should be in there.  Return TRUE if a replacement was
     done that my require an EH edge purge.  */
  
  bool 
  maybe_clean_or_replace_eh_stmt (tree old_stmt, tree new_stmt) 
  {
    int region_nr = lookup_stmt_eh_region (old_stmt);
  
    if (region_nr >= 0)
      {
        bool new_stmt_could_throw = tree_could_throw_p (new_stmt);
  
        if (new_stmt == old_stmt && new_stmt_could_throw)
  	return false;
  
        remove_stmt_from_eh_region (old_stmt);
        if (new_stmt_could_throw)
  	{
  	  add_stmt_to_eh_region (new_stmt, region_nr);
  	  return false;
  	}
        else
  	return true;
      }
  
    return false;
  }
  
  /* Returns TRUE if oneh and twoh are exception handlers (op 1 of
     TRY_CATCH_EXPR or TRY_FINALLY_EXPR that are similar enough to be
     considered the same.  Currently this only handles handlers consisting of
     a single call, as that's the important case for C++: a destructor call
     for a particular object showing up in multiple handlers.  */
  
  static bool
  same_handler_p (tree oneh, tree twoh)
  {
    tree_stmt_iterator i;
    tree ones, twos;
    int ai;
  
    i = tsi_start (oneh);
    if (!tsi_one_before_end_p (i))
      return false;
    ones = tsi_stmt (i);
  
    i = tsi_start (twoh);
    if (!tsi_one_before_end_p (i))
      return false;
    twos = tsi_stmt (i);
  
    if (TREE_CODE (ones) != CALL_EXPR
        || TREE_CODE (twos) != CALL_EXPR
        || !operand_equal_p (CALL_EXPR_FN (ones), CALL_EXPR_FN (twos), 0)
        || call_expr_nargs (ones) != call_expr_nargs (twos))
      return false;
  
    for (ai = 0; ai < call_expr_nargs (ones); ++ai)
      if (!operand_equal_p (CALL_EXPR_ARG (ones, ai),
  			  CALL_EXPR_ARG (twos, ai), 0))
        return false;
  
    return true;
  }
  
  /* Optimize
      try { A() } finally { try { ~B() } catch { ~A() } }
      try { ... } finally { ~A() }
     into
      try { A() } catch { ~B() }
      try { ~B() ... } finally { ~A() }
  
     This occurs frequently in C++, where A is a local variable and B is a
     temporary used in the initializer for A.  */
  
  static void
  optimize_double_finally (tree one, tree two)
  {
    tree oneh;
    tree_stmt_iterator i;
  
    i = tsi_start (TREE_OPERAND (one, 1));
    if (!tsi_one_before_end_p (i))
      return;
  
    oneh = tsi_stmt (i);
    if (TREE_CODE (oneh) != TRY_CATCH_EXPR)
      return;
  
    if (same_handler_p (TREE_OPERAND (oneh, 1), TREE_OPERAND (two, 1)))
      {
        tree b = TREE_OPERAND (oneh, 0);
        TREE_OPERAND (one, 1) = b;
        TREE_SET_CODE (one, TRY_CATCH_EXPR);
  
        i = tsi_start (TREE_OPERAND (two, 0));
        tsi_link_before (&i, unsave_expr_now (b), TSI_SAME_STMT);
      }
  }
  
  /* Perform EH refactoring optimizations that are simpler to do when code
     flow has been lowered but EH structures haven't.  */
  
  static void
  refactor_eh_r (tree t)
  {
   tailrecurse:
    switch (TREE_CODE (t))
      {
      case TRY_FINALLY_EXPR:
      case TRY_CATCH_EXPR:
        refactor_eh_r (TREE_OPERAND (t, 0));
        t = TREE_OPERAND (t, 1);
        goto tailrecurse;
  
      case CATCH_EXPR:
        t = CATCH_BODY (t);
        goto tailrecurse;
  
      case EH_FILTER_EXPR:
        t = EH_FILTER_FAILURE (t);
        goto tailrecurse;
  
      case STATEMENT_LIST:
        {
  	tree_stmt_iterator i;
  	tree one = NULL_TREE, two = NULL_TREE;
  	/* Try to refactor double try/finally.  */
  	for (i = tsi_start (t); !tsi_end_p (i); tsi_next (&i))
  	  {
  	    one = two;
  	    two = tsi_stmt (i);
  	    if (one && two
  		&& TREE_CODE (one) == TRY_FINALLY_EXPR
  		&& TREE_CODE (two) == TRY_FINALLY_EXPR)
  	      optimize_double_finally (one, two);
  	    if (one)
  	      refactor_eh_r (one);
  	  }
  	if (two)
  	  {
  	    t = two;
  	    goto tailrecurse;
  	  }
        }
        break;
  
      default:
        /* A type, a decl, or some kind of statement that we're not
  	 interested in.  Don't walk them.  */
        break;
      }
  }
  
  static unsigned
  refactor_eh (void)
  {
    refactor_eh_r (DECL_SAVED_TREE (current_function_decl));
    return 0;
  }
  
  struct tree_opt_pass pass_refactor_eh =
  {
    "ehopt",				/* name */
    NULL,					/* gate */
    refactor_eh,				/* execute */
    NULL,					/* sub */
    NULL,					/* next */
    0,					/* static_pass_number */
    TV_TREE_EH,				/* tv_id */
    PROP_gimple_lcf,			/* properties_required */
    0,					/* properties_provided */
    0,					/* properties_destroyed */
    0,					/* todo_flags_start */
    TODO_dump_func,			/* todo_flags_finish */
    0					/* letter */
  };
  