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/* 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"

/* 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;

  /* ??? For the benefit of calls.c, converting all this to rtl,

     we need to record the call expression, not just the outer

     modify statement.  */

  if (TREE_CODE (t) == MODIFY_EXPR

      && (t = get_call_expr_in (t)))

    add_stmt_to_eh_region_fn (ifun, t, num);

}

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);

      /* ??? For the benefit of calls.c, converting all this to rtl,

         we need to record the call expression, not just the outer

         modify statement.  */

      if (TREE_CODE (t) == MODIFY_EXPR

          && (t = get_call_expr_in (t)))

        remove_stmt_from_eh_region_fn (ifun, t);

      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, tree t)

{

  struct throw_stmt_node *p, n;

  if (!get_eh_throw_stmt_table (ifun))

    return -2;

  n.stmt = 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 (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;

  /* 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 *);

/* Comparison function for qsort/bsearch.  We're interested in

   searching goto queue elements for source statements.  */

static int

goto_queue_cmp (const void *x, const void *y)

{

  tree a = ((const struct goto_queue_node *)x)->stmt;

  tree b = ((const struct goto_queue_node *)y)->stmt;

  return (a == b ? 0 : a < b ? -1 : 1);

}

/* Search for STMT in the goto queue.  Return the replacement,

   or null if the statement isn't in the queue.  */

static tree

find_goto_replacement (struct leh_tf_state *tf, tree stmt)

{

  struct goto_queue_node tmp, *ret;

  tmp.stmt = stmt;

  ret = (struct goto_queue_node *)

     bsearch (&tmp, tf->goto_queue, tf->goto_queue_active,

                 sizeof (struct goto_queue_node), goto_queue_cmp);

  return (ret ? ret->repl_stmt : 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 ();

    }

  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 MODIFY_EXPR:

          {

            tree result = TREE_OPERAND (ret_expr, 0);

            tree new, old = TREE_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 = build2 (MODIFY_EXPR, TREE_TYPE (new), new, old);

            append_to_statement_list (x, &q->repl_stmt);

            if (new == result)

              x = result;

            else

              x = build2 (MODIFY_EXPR, TREE_TYPE (result), 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);