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/* Tree lowering pass.  Lowers GIMPLE into unstructured form.

   Copyright (C) 2003, 2005, 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 "varray.h"

#include "tree-gimple.h"

#include "tree-inline.h"

#include "diagnostic.h"

#include "langhooks.h"

#include "langhooks-def.h"

#include "tree-flow.h"

#include "timevar.h"

#include "except.h"

#include "hashtab.h"

#include "flags.h"

#include "function.h"

#include "expr.h"

#include "toplev.h"

#include "tree-pass.h"

struct lower_data

{

  /* Block the current statement belongs to.  */

  tree block;

  /* A TREE_LIST of label and return statements to be moved to the end

     of the function.  */

  tree return_statements;

  /* True if the function calls __builtin_setjmp.  */

  bool calls_builtin_setjmp;

};

static void lower_stmt (tree_stmt_iterator *, struct lower_data *);

static void lower_bind_expr (tree_stmt_iterator *, struct lower_data *);

static void lower_cond_expr (tree_stmt_iterator *, struct lower_data *);

static void lower_return_expr (tree_stmt_iterator *, struct lower_data *);

static void lower_builtin_setjmp (tree_stmt_iterator *);

/* Lower the body of current_function_decl.  */

static unsigned int

lower_function_body (void)

{

  struct lower_data data;

  tree *body_p = &DECL_SAVED_TREE (current_function_decl);

  tree bind = *body_p;

  tree_stmt_iterator i;

  tree t, x;

  gcc_assert (TREE_CODE (bind) == BIND_EXPR);

  memset (&data, 0, sizeof (data));

  data.block = DECL_INITIAL (current_function_decl);

  BLOCK_SUBBLOCKS (data.block) = NULL_TREE;

  BLOCK_CHAIN (data.block) = NULL_TREE;

  TREE_ASM_WRITTEN (data.block) = 1;

  *body_p = alloc_stmt_list ();

  i = tsi_start (*body_p);

  tsi_link_after (&i, bind, TSI_NEW_STMT);

  lower_bind_expr (&i, &data);

  i = tsi_last (*body_p);

  /* If the function falls off the end, we need a null return statement.

     If we've already got one in the return_statements list, we don't

     need to do anything special.  Otherwise build one by hand.  */

  if (block_may_fallthru (*body_p)

      && (data.return_statements == NULL

          || TREE_OPERAND (TREE_VALUE (data.return_statements), 0) != NULL))

    {

      x = build1 (RETURN_EXPR, void_type_node, NULL);

      SET_EXPR_LOCATION (x, cfun->function_end_locus);

      tsi_link_after (&i, x, TSI_CONTINUE_LINKING);

    }

  /* If we lowered any return statements, emit the representative

     at the end of the function.  */

  for (t = data.return_statements ; t ; t = TREE_CHAIN (t))

    {

      x = build1 (LABEL_EXPR, void_type_node, TREE_PURPOSE (t));

      tsi_link_after (&i, x, TSI_CONTINUE_LINKING);

      /* Remove the line number from the representative return statement.

         It now fills in for many such returns.  Failure to remove this

         will result in incorrect results for coverage analysis.  */

      x = TREE_VALUE (t);

#ifdef USE_MAPPED_LOCATION

      SET_EXPR_LOCATION (x, UNKNOWN_LOCATION);

#else

      SET_EXPR_LOCUS (x, NULL);

#endif

      tsi_link_after (&i, x, TSI_CONTINUE_LINKING);

    }

  /* If the function calls __builtin_setjmp, we need to emit the computed

     goto that will serve as the unique dispatcher for all the receivers.  */

  if (data.calls_builtin_setjmp)

    {

      tree disp_label, disp_var, arg;

      /* Build 'DISP_LABEL:' and insert.  */

      disp_label = create_artificial_label ();

      /* This mark will create forward edges from every call site.  */

      DECL_NONLOCAL (disp_label) = 1;

      current_function_has_nonlocal_label = 1;

      x = build1 (LABEL_EXPR, void_type_node, disp_label);

      tsi_link_after (&i, x, TSI_CONTINUE_LINKING);

      /* Build 'DISP_VAR = __builtin_setjmp_dispatcher (DISP_LABEL);'

         and insert.  */

      disp_var = create_tmp_var (ptr_type_node, "setjmpvar");

      t = build_addr (disp_label, current_function_decl);

      arg = tree_cons (NULL, t, NULL);

      t = implicit_built_in_decls[BUILT_IN_SETJMP_DISPATCHER];

      t = build_function_call_expr (t,arg);

      x = build2 (MODIFY_EXPR, void_type_node, disp_var, t);

      /* Build 'goto DISP_VAR;' and insert.  */

      tsi_link_after (&i, x, TSI_CONTINUE_LINKING);

      x = build1 (GOTO_EXPR, void_type_node, disp_var);

      tsi_link_after (&i, x, TSI_CONTINUE_LINKING);

    }

  gcc_assert (data.block == DECL_INITIAL (current_function_decl));

  BLOCK_SUBBLOCKS (data.block)

    = blocks_nreverse (BLOCK_SUBBLOCKS (data.block));

  clear_block_marks (data.block);

  return 0;

}

struct tree_opt_pass pass_lower_cf =

{

  "lower",                              /* name */

  NULL,                                 /* gate */

  lower_function_body,                  /* execute */

  NULL,                                 /* sub */

  NULL,                                 /* next */

  0,                                     /* static_pass_number */

  0,                                     /* tv_id */

  PROP_gimple_any,                      /* properties_required */

  PROP_gimple_lcf,                      /* properties_provided */

  0,                                     /* properties_destroyed */

  0,                                     /* todo_flags_start */

  TODO_dump_func,                       /* todo_flags_finish */

};

/* Lower the EXPR.  Unlike gimplification the statements are not relowered

   when they are changed -- if this has to be done, the lowering routine must

   do it explicitly.  DATA is passed through the recursion.  */

static void

lower_stmt_body (tree expr, struct lower_data *data)

{

  tree_stmt_iterator tsi;

  for (tsi = tsi_start (expr); !tsi_end_p (tsi); )

    lower_stmt (&tsi, data);

}

/* Lower the OpenMP directive statement pointed by TSI.  DATA is

   passed through the recursion.  */

static void

lower_omp_directive (tree_stmt_iterator *tsi, struct lower_data *data)

{

  tree stmt;

  stmt = tsi_stmt (*tsi);

  lower_stmt_body (OMP_BODY (stmt), data);

  tsi_link_before (tsi, stmt, TSI_SAME_STMT);

  tsi_link_before (tsi, OMP_BODY (stmt), TSI_SAME_STMT);

  OMP_BODY (stmt) = NULL_TREE;

  tsi_delink (tsi);

}

/* Lower statement TSI.  DATA is passed through the recursion.  */

static void

lower_stmt (tree_stmt_iterator *tsi, struct lower_data *data)

{

  tree stmt = tsi_stmt (*tsi);

  if (EXPR_HAS_LOCATION (stmt) && data)

    TREE_BLOCK (stmt) = data->block;

  switch (TREE_CODE (stmt))

    {

    case BIND_EXPR:

      lower_bind_expr (tsi, data);

      return;

    case COND_EXPR:

      lower_cond_expr (tsi, data);

      return;

    case RETURN_EXPR:

      lower_return_expr (tsi, data);

      return;

    case TRY_FINALLY_EXPR:

    case TRY_CATCH_EXPR:

      lower_stmt_body (TREE_OPERAND (stmt, 0), data);

      lower_stmt_body (TREE_OPERAND (stmt, 1), data);

      break;

    case CATCH_EXPR:

      lower_stmt_body (CATCH_BODY (stmt), data);

      break;

    case EH_FILTER_EXPR:

      lower_stmt_body (EH_FILTER_FAILURE (stmt), data);

      break;

    case NOP_EXPR:

    case ASM_EXPR:

    case GOTO_EXPR:

    case LABEL_EXPR:

    case SWITCH_EXPR:

    case OMP_FOR:

    case OMP_SECTIONS:

    case OMP_SECTION:

    case OMP_SINGLE:

    case OMP_MASTER:

    case OMP_ORDERED:

    case OMP_CRITICAL:

    case OMP_RETURN:

    case OMP_CONTINUE:

      break;

    case MODIFY_EXPR:

      if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)

        stmt = TREE_OPERAND (stmt, 1);

      else

        break;

      /* FALLTHRU */

    case CALL_EXPR:

      {

        tree decl = get_callee_fndecl (stmt);

        if (decl

            && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL

            && DECL_FUNCTION_CODE (decl) == BUILT_IN_SETJMP)

          {

            data->calls_builtin_setjmp = true;

            lower_builtin_setjmp (tsi);

            return;

          }

      }

      break;

    case OMP_PARALLEL:

      lower_omp_directive (tsi, data);

      return;

    default:

      gcc_unreachable ();

    }

  tsi_next (tsi);

}

/* Lower a bind_expr TSI.  DATA is passed through the recursion.  */

static void

lower_bind_expr (tree_stmt_iterator *tsi, struct lower_data *data)

{

  tree old_block = data->block;

  tree stmt = tsi_stmt (*tsi);

  tree new_block = BIND_EXPR_BLOCK (stmt);

  if (new_block)

    {

      if (new_block == old_block)

        {

          /* The outermost block of the original function may not be the

             outermost statement chain of the gimplified function.  So we

             may see the outermost block just inside the function.  */

          gcc_assert (new_block == DECL_INITIAL (current_function_decl));

          new_block = NULL;

        }

      else

        {

          /* We do not expect to handle duplicate blocks.  */

          gcc_assert (!TREE_ASM_WRITTEN (new_block));

          TREE_ASM_WRITTEN (new_block) = 1;

          /* Block tree may get clobbered by inlining.  Normally this would

             be fixed in rest_of_decl_compilation using block notes, but

             since we are not going to emit them, it is up to us.  */

          BLOCK_CHAIN (new_block) = BLOCK_SUBBLOCKS (old_block);

          BLOCK_SUBBLOCKS (old_block) = new_block;

          BLOCK_SUBBLOCKS (new_block) = NULL_TREE;

          BLOCK_SUPERCONTEXT (new_block) = old_block;

          data->block = new_block;

        }

    }

  record_vars (BIND_EXPR_VARS (stmt));

  lower_stmt_body (BIND_EXPR_BODY (stmt), data);

  if (new_block)

    {

      gcc_assert (data->block == new_block);

      BLOCK_SUBBLOCKS (new_block)

        = blocks_nreverse (BLOCK_SUBBLOCKS (new_block));

      data->block = old_block;

    }

  /* The BIND_EXPR no longer carries any useful information -- kill it.  */

  tsi_link_before (tsi, BIND_EXPR_BODY (stmt), TSI_SAME_STMT);

  tsi_delink (tsi);

}

/* Try to determine whether a TRY_CATCH expression can fall through.

   This is a subroutine of block_may_fallthru.  */

static bool

try_catch_may_fallthru (tree stmt)

{

  tree_stmt_iterator i;

  /* If the TRY block can fall through, the whole TRY_CATCH can

     fall through.  */

  if (block_may_fallthru (TREE_OPERAND (stmt, 0)))

    return true;

  i = tsi_start (TREE_OPERAND (stmt, 1));

  switch (TREE_CODE (tsi_stmt (i)))

    {

    case CATCH_EXPR:

      /* We expect to see a sequence of CATCH_EXPR trees, each with a

         catch expression and a body.  The whole TRY_CATCH may fall

         through iff any of the catch bodies falls through.  */

      for (; !tsi_end_p (i); tsi_next (&i))

        {

          if (block_may_fallthru (CATCH_BODY (tsi_stmt (i))))

            return true;

        }

      return false;

    case EH_FILTER_EXPR:

      /* The exception filter expression only matters if there is an

         exception.  If the exception does not match EH_FILTER_TYPES,

         we will execute EH_FILTER_FAILURE, and we will fall through

         if that falls through.  If the exception does match

         EH_FILTER_TYPES, the stack unwinder will continue up the

         stack, so we will not fall through.  We don't know whether we

         will throw an exception which matches EH_FILTER_TYPES or not,

         so we just ignore EH_FILTER_TYPES and assume that we might

         throw an exception which doesn't match.  */

      return block_may_fallthru (EH_FILTER_FAILURE (tsi_stmt (i)));

    default:

      /* This case represents statements to be executed when an

         exception occurs.  Those statements are implicitly followed

         by a RESX_EXPR to resume execution after the exception.  So

         in this case the TRY_CATCH never falls through.  */

      return false;

    }

}

/* Try to determine if we can fall out of the bottom of BLOCK.  This guess

   need not be 100% accurate; simply be conservative and return true if we

   don't know.  This is used only to avoid stupidly generating extra code.

   If we're wrong, we'll just delete the extra code later.  */

bool

block_may_fallthru (tree block)

{

  tree stmt = expr_last (block);

  switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)

    {

    case GOTO_EXPR:

    case RETURN_EXPR:

    case RESX_EXPR:

      /* Easy cases.  If the last statement of the block implies

         control transfer, then we can't fall through.  */

      return false;

    case SWITCH_EXPR:

      /* If SWITCH_LABELS is set, this is lowered, and represents a

         branch to a selected label and hence can not fall through.

         Otherwise SWITCH_BODY is set, and the switch can fall

         through.  */

      return SWITCH_LABELS (stmt) == NULL_TREE;

    case COND_EXPR:

      if (block_may_fallthru (COND_EXPR_THEN (stmt)))

        return true;

      return block_may_fallthru (COND_EXPR_ELSE (stmt));

    case BIND_EXPR:

      return block_may_fallthru (BIND_EXPR_BODY (stmt));

    case TRY_CATCH_EXPR:

      return try_catch_may_fallthru (stmt);

    case TRY_FINALLY_EXPR:

      /* The finally clause is always executed after the try clause,

         so if it does not fall through, then the try-finally will not

         fall through.  Otherwise, if the try clause does not fall

         through, then when the finally clause falls through it will

         resume execution wherever the try clause was going.  So the

         whole try-finally will only fall through if both the try

         clause and the finally clause fall through.  */

      return (block_may_fallthru (TREE_OPERAND (stmt, 0))

              && block_may_fallthru (TREE_OPERAND (stmt, 1)));

    case MODIFY_EXPR:

      if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)

        stmt = TREE_OPERAND (stmt, 1);

      else

        return true;

      /* FALLTHRU */

    case CALL_EXPR:

      /* Functions that do not return do not fall through.  */

      return (call_expr_flags (stmt) & ECF_NORETURN) == 0;

    case CLEANUP_POINT_EXPR:

      return block_may_fallthru (TREE_OPERAND (stmt, 0));

    default:

      return true;

    }

}

/* Lower a cond_expr TSI.  DATA is passed through the recursion.  */

static void

lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)

{

  tree stmt = tsi_stmt (*tsi);

  bool then_is_goto, else_is_goto;

  tree then_branch, else_branch;

  tree then_goto, else_goto;

  then_branch = COND_EXPR_THEN (stmt);

  else_branch = COND_EXPR_ELSE (stmt);

  lower_stmt_body (then_branch, data);

  lower_stmt_body (else_branch, data);

  then_goto = expr_only (then_branch);

  then_is_goto = then_goto && simple_goto_p (then_goto);

  else_goto = expr_only (else_branch);

  else_is_goto = else_goto && simple_goto_p (else_goto);

  if (!then_is_goto || !else_is_goto)

    {

      tree then_label, else_label, end_label, t;

      then_label = NULL_TREE;

      else_label = NULL_TREE;

      end_label = NULL_TREE;

      /* Replace the cond_expr with explicit gotos.  */

      if (!then_is_goto)

        {

          t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);

          if (TREE_SIDE_EFFECTS (then_branch))

            then_label = t;

          else

            end_label = t;

          then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));

        }

      if (!else_is_goto)

        {

          t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);

          if (TREE_SIDE_EFFECTS (else_branch))

            else_label = t;

          else

            {

              /* Both THEN and ELSE can be no-ops if one or both contained an

                 empty BIND_EXPR that was associated with the toplevel block

                 of an inlined function.  In that case remove_useless_stmts

                 can't have cleaned things up for us; kill the whole

                 conditional now.  */

              if (end_label)

                {

                  tsi_delink (tsi);

                  return;

                }

              else

                end_label = t;

            }

          else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));

        }

      if (then_label)

        {

          bool may_fallthru = block_may_fallthru (then_branch);

          tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);

          tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);

          if (else_label && may_fallthru)

            {

              end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);

              t = build_and_jump (&LABEL_EXPR_LABEL (end_label));

              tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);

            }

        }

      if (else_label)

        {

          tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);

          tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);

        }

      if (end_label)

        tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);

    }

  COND_EXPR_THEN (stmt) = then_goto;

  COND_EXPR_ELSE (stmt) = else_goto;

  tsi_next (tsi);

}

/* Lower a return_expr TSI.  DATA is passed through the recursion.  */

static void

lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)

{

  tree stmt = tsi_stmt (*tsi);

  tree value, t, label;

  /* Extract the value being returned.  */

  value = TREE_OPERAND (stmt, 0);

  if (value && TREE_CODE (value) == MODIFY_EXPR)

    value = TREE_OPERAND (value, 1);

  /* Match this up with an existing return statement that's been created.  */

  for (t = data->return_statements; t ; t = TREE_CHAIN (t))

    {

      tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);

      if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)

        tvalue = TREE_OPERAND (tvalue, 1);

      if (value == tvalue)

        {

          label = TREE_PURPOSE (t);

          goto found;

        }

    }

  /* Not found.  Create a new label and record the return statement.  */

  label = create_artificial_label ();

  data->return_statements = tree_cons (label, stmt, data->return_statements);

  /* Generate a goto statement and remove the return statement.  */

 found:

  t = build1 (GOTO_EXPR, void_type_node, label);

  SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));

  tsi_link_before (tsi, t, TSI_SAME_STMT);

  tsi_delink (tsi);

}

/* Lower a __builtin_setjmp TSI.

   __builtin_setjmp is passed a pointer to an array of five words (not

   all will be used on all machines).  It operates similarly to the C

   library function of the same name, but is more efficient.

   It is lowered into 3 other builtins, namely __builtin_setjmp_setup,

   __builtin_setjmp_dispatcher and __builtin_setjmp_receiver, but with

   __builtin_setjmp_dispatcher shared among all the instances; that's

   why it is only emitted at the end by lower_function_body.

   After full lowering, the body of the function should look like:

    {

      void * setjmpvar.0;

      int D.1844;

      int D.2844;

      [...]

      __builtin_setjmp_setup (&buf, &<D1847>);

      D.1844 = 0;

      goto <D1846>;

      <D1847>:;

      __builtin_setjmp_receiver (&<D1847>);

      D.1844 = 1;

      <D1846>:;

      if (D.1844 == 0) goto <D1848>; else goto <D1849>;

      [...]

      __builtin_setjmp_setup (&buf, &<D2847>);

      D.2844 = 0;

      goto <D2846>;

      <D2847>:;

      __builtin_setjmp_receiver (&<D2847>);

      D.2844 = 1;

      <D2846>:;

      if (D.2844 == 0) goto <D2848>; else goto <D2849>;

      [...]

      <D3850>:;

      return;

      <D3853>: [non-local];

      setjmpvar.0 = __builtin_setjmp_dispatcher (&<D3853>);

      goto setjmpvar.0;

    }

   The dispatcher block will be both the unique destination of all the

   abnormal call edges and the unique source of all the abnormal edges

   to the receivers, thus keeping the complexity explosion localized.  */

static void

lower_builtin_setjmp (tree_stmt_iterator *tsi)

{

  tree stmt = tsi_stmt (*tsi);

  tree cont_label = create_artificial_label ();

  tree next_label = create_artificial_label ();

  tree dest, t, arg;

  /* NEXT_LABEL is the label __builtin_longjmp will jump to.  Its address is

     passed to both __builtin_setjmp_setup and __builtin_setjmp_receiver.  */

  FORCED_LABEL (next_label) = 1;

  if (TREE_CODE (stmt) == MODIFY_EXPR)

    {

      dest = TREE_OPERAND (stmt, 0);

      stmt = TREE_OPERAND (stmt, 1);

    }

  else

    dest = NULL_TREE;

  /* Build '__builtin_setjmp_setup (BUF, NEXT_LABEL)' and insert.  */

  t = build_addr (next_label, current_function_decl);

  arg = tree_cons (NULL, t, NULL);

  t = TREE_VALUE (TREE_OPERAND (stmt, 1));

  arg = tree_cons (NULL, t, arg);

  t = implicit_built_in_decls[BUILT_IN_SETJMP_SETUP];

  t = build_function_call_expr (t, arg);

  SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));

  tsi_link_before (tsi, t, TSI_SAME_STMT);

  /* Build 'DEST = 0' and insert.  */

  if (dest)

    {

      t = build2 (MODIFY_EXPR, void_type_node, dest, integer_zero_node);

      SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));

      tsi_link_before (tsi, t, TSI_SAME_STMT);

    }

  /* Build 'goto CONT_LABEL' and insert.  */

  t = build1 (GOTO_EXPR, void_type_node, cont_label);

  tsi_link_before (tsi, t, TSI_SAME_STMT);

  /* Build 'NEXT_LABEL:' and insert.  */

  t = build1 (LABEL_EXPR, void_type_node, next_label);

  tsi_link_before (tsi, t, TSI_SAME_STMT);

  /* Build '__builtin_setjmp_receiver (NEXT_LABEL)' and insert.  */

  t = build_addr (next_label, current_function_decl);

  arg = tree_cons (NULL, t, NULL);

  t = implicit_built_in_decls[BUILT_IN_SETJMP_RECEIVER];

  t = build_function_call_expr (t, arg);

  SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));

  tsi_link_before (tsi, t, TSI_SAME_STMT);

  /* Build 'DEST = 1' and insert.  */

  if (dest)

    {

      t = build2 (MODIFY_EXPR, void_type_node, dest, integer_one_node);

      SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));

      tsi_link_before (tsi, t, TSI_SAME_STMT);

    }

  /* Build 'CONT_LABEL:' and insert.  */

  t = build1 (LABEL_EXPR, void_type_node, cont_label);

  tsi_link_before (tsi, t, TSI_SAME_STMT);

  /* Remove the call to __builtin_setjmp.  */

  tsi_delink (tsi);

}