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/* GIMPLE lowering pass.  Converts High GIMPLE into Low GIMPLE.

   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010

   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 "gimple.h"

#include "tree-iterator.h"

#include "tree-inline.h"

#include "tree-flow.h"

#include "flags.h"

#include "function.h"

#include "diagnostic-core.h"

#include "tree-pass.h"

/* The differences between High GIMPLE and Low GIMPLE are the

   following:

   1- Lexical scopes are removed (i.e., GIMPLE_BIND disappears).

   2- GIMPLE_TRY and GIMPLE_CATCH are converted to abnormal control

      flow and exception regions are built as an on-the-side region

      hierarchy (See tree-eh.c:lower_eh_constructs).

   3- Multiple identical return statements are grouped into a single

      return and gotos to the unique return site.  */

/* Match a return statement with a label.  During lowering, we identify

   identical return statements and replace duplicates with a jump to

   the corresponding label.  */

struct return_statements_t

{

  tree label;

  gimple stmt;

};

typedef struct return_statements_t return_statements_t;

DEF_VEC_O(return_statements_t);

DEF_VEC_ALLOC_O(return_statements_t,heap);

struct lower_data

{

  /* Block the current statement belongs to.  */

  tree block;

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

     of the function.  */

  VEC(return_statements_t,heap) *return_statements;

  /* True if the current statement cannot fall through.  */

  bool cannot_fallthru;

  /* True if the function calls __builtin_setjmp.  */

  bool calls_builtin_setjmp;

};

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

static void lower_gimple_bind (gimple_stmt_iterator *, struct lower_data *);

static void lower_gimple_return (gimple_stmt_iterator *, struct lower_data *);

static void lower_builtin_setjmp (gimple_stmt_iterator *);

/* Lower the body of current_function_decl from High GIMPLE into Low

   GIMPLE.  */

static unsigned int

lower_function_body (void)

{

  struct lower_data data;

  gimple_seq body = gimple_body (current_function_decl);

  gimple_seq lowered_body;

  gimple_stmt_iterator i;

  gimple bind;

  tree t;

  gimple x;

  /* The gimplifier should've left a body of exactly one statement,

     namely a GIMPLE_BIND.  */

  gcc_assert (gimple_seq_first (body) == gimple_seq_last (body)

              && gimple_code (gimple_seq_first_stmt (body)) == GIMPLE_BIND);

  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;

  data.return_statements = VEC_alloc (return_statements_t, heap, 8);

  bind = gimple_seq_first_stmt (body);

  lowered_body = NULL;

  gimple_seq_add_stmt (&lowered_body, bind);

  i = gsi_start (lowered_body);

  lower_gimple_bind (&i, &data);

  /* Once the old body has been lowered, replace it with the new

     lowered sequence.  */

  gimple_set_body (current_function_decl, lowered_body);

  i = gsi_last (lowered_body);

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

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

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

  if (gimple_seq_may_fallthru (lowered_body)

      && (VEC_empty (return_statements_t, data.return_statements)

          || gimple_return_retval (VEC_last (return_statements_t,

                                   data.return_statements)->stmt) != NULL))

    {

      x = gimple_build_return (NULL);

      gimple_set_location (x, cfun->function_end_locus);

      gimple_set_block (x, DECL_INITIAL (current_function_decl));

      gsi_insert_after (&i, x, GSI_CONTINUE_LINKING);

    }

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

     at the end of the function.  */

  while (!VEC_empty (return_statements_t, data.return_statements))

    {

      return_statements_t t;

      /* Unfortunately, we can't use VEC_pop because it returns void for

         objects.  */

      t = *VEC_last (return_statements_t, data.return_statements);

      VEC_truncate (return_statements_t,

                    data.return_statements,

                    VEC_length (return_statements_t,

                                data.return_statements) - 1);

      x = gimple_build_label (t.label);

      gsi_insert_after (&i, x, GSI_CONTINUE_LINKING);

      gsi_insert_after (&i, t.stmt, GSI_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 (cfun->function_end_locus);

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

      DECL_NONLOCAL (disp_label) = 1;

      cfun->has_nonlocal_label = 1;

      x = gimple_build_label (disp_label);

      gsi_insert_after (&i, x, GSI_CONTINUE_LINKING);

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

         and insert.  */

      disp_var = create_tmp_var (ptr_type_node, "setjmpvar");

      arg = build_addr (disp_label, current_function_decl);

      t = builtin_decl_implicit (BUILT_IN_SETJMP_DISPATCHER);

      x = gimple_build_call (t, 1, arg);

      gimple_call_set_lhs (x, disp_var);

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

      gsi_insert_after (&i, x, GSI_CONTINUE_LINKING);

      x = gimple_build_goto (disp_var);

      gsi_insert_after (&i, x, GSI_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);

  VEC_free(return_statements_t, heap, data.return_statements);

  return 0;

}

struct gimple_opt_pass pass_lower_cf =

{

 {

  GIMPLE_PASS,

  "lower",                              /* name */

  NULL,                                 /* gate */

  lower_function_body,                  /* execute */

  NULL,                                 /* sub */

  NULL,                                 /* next */

  0,                                     /* static_pass_number */

  TV_NONE,                              /* tv_id */

  PROP_gimple_any,                      /* properties_required */

  PROP_gimple_lcf,                      /* properties_provided */

  0,                                     /* properties_destroyed */

  0,                                     /* todo_flags_start */

 }

};

/* Verify if the type of the argument matches that of the function

   declaration.  If we cannot verify this or there is a mismatch,

   return false.  */

static bool

gimple_check_call_args (gimple stmt, tree fndecl)

{

  tree parms, p;

  unsigned int i, nargs;

  /* Calls to internal functions always match their signature.  */

  if (gimple_call_internal_p (stmt))

    return true;

  nargs = gimple_call_num_args (stmt);

  /* Get argument types for verification.  */

  if (fndecl)

    parms = TYPE_ARG_TYPES (TREE_TYPE (fndecl));

  else

    parms = TYPE_ARG_TYPES (gimple_call_fntype (stmt));

  /* Verify if the type of the argument matches that of the function

     declaration.  If we cannot verify this or there is a mismatch,

     return false.  */

  if (fndecl && DECL_ARGUMENTS (fndecl))

    {

      for (i = 0, p = DECL_ARGUMENTS (fndecl);

           i < nargs;

           i++, p = DECL_CHAIN (p))

        {

          /* We cannot distinguish a varargs function from the case

             of excess parameters, still deferring the inlining decision

             to the callee is possible.  */

          if (!p)

            break;

          if (p == error_mark_node

              || gimple_call_arg (stmt, i) == error_mark_node

              || !fold_convertible_p (DECL_ARG_TYPE (p),

                                      gimple_call_arg (stmt, i)))

            return false;

        }

    }

  else if (parms)

    {

      for (i = 0, p = parms; i < nargs; i++, p = TREE_CHAIN (p))

        {

          /* If this is a varargs function defer inlining decision

             to callee.  */

          if (!p)

            break;

          if (TREE_VALUE (p) == error_mark_node

              || gimple_call_arg (stmt, i) == error_mark_node

              || TREE_CODE (TREE_VALUE (p)) == VOID_TYPE

              || !fold_convertible_p (TREE_VALUE (p),

                                      gimple_call_arg (stmt, i)))

            return false;

        }

    }

  else

    {

      if (nargs != 0)

        return false;

    }

  return true;

}

/* Verify if the type of the argument and lhs of CALL_STMT matches

   that of the function declaration CALLEE.

   If we cannot verify this or there is a mismatch, return false.  */

bool

gimple_check_call_matching_types (gimple call_stmt, tree callee)

{

  tree lhs;

  if ((DECL_RESULT (callee)

       && !DECL_BY_REFERENCE (DECL_RESULT (callee))

       && (lhs = gimple_call_lhs (call_stmt)) != NULL_TREE

       && !useless_type_conversion_p (TREE_TYPE (DECL_RESULT (callee)),

                                      TREE_TYPE (lhs))

       && !fold_convertible_p (TREE_TYPE (DECL_RESULT (callee)), lhs))

      || !gimple_check_call_args (call_stmt, callee))

    return false;

  return true;

}

/* Lower sequence SEQ.  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_sequence (gimple_seq seq, struct lower_data *data)

{

  gimple_stmt_iterator gsi;

  for (gsi = gsi_start (seq); !gsi_end_p (gsi); )

    lower_stmt (&gsi, data);

}

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

   passed through the recursion.  */

static void

lower_omp_directive (gimple_stmt_iterator *gsi, struct lower_data *data)

{

  gimple stmt;

  stmt = gsi_stmt (*gsi);

  lower_sequence (gimple_omp_body (stmt), data);

  gsi_insert_before (gsi, stmt, GSI_SAME_STMT);

  gsi_insert_seq_before (gsi, gimple_omp_body (stmt), GSI_SAME_STMT);

  gimple_omp_set_body (stmt, NULL);

  gsi_remove (gsi, false);

}

/* Lower statement GSI.  DATA is passed through the recursion.  We try to

   track the fallthruness of statements and get rid of unreachable return

   statements in order to prevent the EH lowering pass from adding useless

   edges that can cause bogus warnings to be issued later; this guess need

   not be 100% accurate, simply be conservative and reset cannot_fallthru

   to false if we don't know.  */

static void

lower_stmt (gimple_stmt_iterator *gsi, struct lower_data *data)

{

  gimple stmt = gsi_stmt (*gsi);

  gimple_set_block (stmt, data->block);

  switch (gimple_code (stmt))

    {

    case GIMPLE_BIND:

      lower_gimple_bind (gsi, data);

      /* Propagate fallthruness.  */

      return;

    case GIMPLE_COND:

    case GIMPLE_GOTO:

    case GIMPLE_SWITCH:

      data->cannot_fallthru = true;

      gsi_next (gsi);

      return;

    case GIMPLE_RETURN:

      if (data->cannot_fallthru)

        {

          gsi_remove (gsi, false);

          /* Propagate fallthruness.  */

        }

      else

        {

          lower_gimple_return (gsi, data);

          data->cannot_fallthru = true;

        }

      return;

    case GIMPLE_TRY:

      {

        bool try_cannot_fallthru;

        lower_sequence (gimple_try_eval (stmt), data);

        try_cannot_fallthru = data->cannot_fallthru;

        data->cannot_fallthru = false;

        lower_sequence (gimple_try_cleanup (stmt), data);

        /* See gimple_stmt_may_fallthru for the rationale.  */

        if (gimple_try_kind (stmt) == GIMPLE_TRY_FINALLY)

          {

            data->cannot_fallthru |= try_cannot_fallthru;

            gsi_next (gsi);

            return;

          }

      }

      break;

    case GIMPLE_CATCH:

      data->cannot_fallthru = false;

      lower_sequence (gimple_catch_handler (stmt), data);

      break;

    case GIMPLE_EH_FILTER:

      data->cannot_fallthru = false;

      lower_sequence (gimple_eh_filter_failure (stmt), data);

      break;

    case GIMPLE_EH_ELSE:

      lower_sequence (gimple_eh_else_n_body (stmt), data);

      lower_sequence (gimple_eh_else_e_body (stmt), data);

      break;

    case GIMPLE_NOP:

    case GIMPLE_ASM:

    case GIMPLE_ASSIGN:

    case GIMPLE_PREDICT:

    case GIMPLE_LABEL:

    case GIMPLE_EH_MUST_NOT_THROW:

    case GIMPLE_OMP_FOR:

    case GIMPLE_OMP_SECTIONS:

    case GIMPLE_OMP_SECTIONS_SWITCH:

    case GIMPLE_OMP_SECTION:

    case GIMPLE_OMP_SINGLE:

    case GIMPLE_OMP_MASTER:

    case GIMPLE_OMP_ORDERED:

    case GIMPLE_OMP_CRITICAL:

    case GIMPLE_OMP_RETURN:

    case GIMPLE_OMP_ATOMIC_LOAD:

    case GIMPLE_OMP_ATOMIC_STORE:

    case GIMPLE_OMP_CONTINUE:

      break;

    case GIMPLE_CALL:

      {

        tree decl = gimple_call_fndecl (stmt);

        if (decl

            && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL

            && DECL_FUNCTION_CODE (decl) == BUILT_IN_SETJMP)

          {

            lower_builtin_setjmp (gsi);

            data->cannot_fallthru = false;

            data->calls_builtin_setjmp = true;

            return;

          }

        if (decl && (flags_from_decl_or_type (decl) & ECF_NORETURN))

          {

            data->cannot_fallthru = true;

            gsi_next (gsi);

            return;

          }

      }

      break;

    case GIMPLE_OMP_PARALLEL:

    case GIMPLE_OMP_TASK:

      data->cannot_fallthru = false;

      lower_omp_directive (gsi, data);

      data->cannot_fallthru = false;

      return;

    case GIMPLE_TRANSACTION:

      lower_sequence (gimple_transaction_body (stmt), data);

      break;

    default:

      gcc_unreachable ();

    }

  data->cannot_fallthru = false;

  gsi_next (gsi);

}

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

static void

lower_gimple_bind (gimple_stmt_iterator *gsi, struct lower_data *data)

{

  tree old_block = data->block;

  gimple stmt = gsi_stmt (*gsi);

  tree new_block = gimple_bind_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 (gimple_bind_vars (stmt));

  lower_sequence (gimple_bind_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 GIMPLE_BIND no longer carries any useful information -- kill it.  */

  gsi_insert_seq_before (gsi, gimple_bind_body (stmt), GSI_SAME_STMT);

  gsi_remove (gsi, false);

}

/* 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 (const_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 statement to resume execution after the exception.

         So in this case the TRY_CATCH never falls through.  */

      return false;

    }

}

/* Same as above, but for a GIMPLE_TRY_CATCH.  */

static bool

gimple_try_catch_may_fallthru (gimple stmt)

{

  gimple_stmt_iterator i;

  /* We don't handle GIMPLE_TRY_FINALLY.  */

  gcc_assert (gimple_try_kind (stmt) == GIMPLE_TRY_CATCH);

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

     fall through.  */

  if (gimple_seq_may_fallthru (gimple_try_eval (stmt)))

    return true;

  i = gsi_start (gimple_try_cleanup (stmt));

  switch (gimple_code (gsi_stmt (i)))

    {

    case GIMPLE_CATCH:

      /* We expect to see a sequence of GIMPLE_CATCH stmts, each with a

         catch expression and a body.  The whole try/catch may fall

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

      for (; !gsi_end_p (i); gsi_next (&i))

        {

          if (gimple_seq_may_fallthru (gimple_catch_handler (gsi_stmt (i))))

            return true;

        }

      return false;

    case GIMPLE_EH_FILTER:

      /* 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 gimple_seq_may_fallthru (gimple_eh_filter_failure (gsi_stmt (i)));

    default:

      /* This case represents statements to be executed when an

         exception occurs.  Those statements are implicitly followed

         by a GIMPLE_RESX 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 (const_tree block)

{

  /* This CONST_CAST is okay because expr_last returns its argument

     unmodified and we assign it to a const_tree.  */

  const_tree stmt = expr_last (CONST_CAST_TREE(block));

  switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)

    {

    case GOTO_EXPR:

    case RETURN_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;

    }

}

/* Try to determine if we can continue executing the statement

   immediately following STMT.  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

gimple_stmt_may_fallthru (gimple stmt)

{

  if (!stmt)

    return true;

  switch (gimple_code (stmt))

    {

    case GIMPLE_GOTO:

    case GIMPLE_RETURN:

    case GIMPLE_RESX:

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

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

      return false;

    case GIMPLE_SWITCH:

      /* Switch has already been lowered and represents a branch

         to a selected label and hence can't fall through.  */

      return false;

    case GIMPLE_COND:

      /* GIMPLE_COND's are already lowered into a two-way branch.  They

         can't fall through.  */

      return false;

    case GIMPLE_BIND:

      return gimple_seq_may_fallthru (gimple_bind_body (stmt));

    case GIMPLE_TRY: