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/* Initialization of uninitialized regs.

   Copyright (C) 2007, 2008, 2009 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 "regs.h"

#include "expr.h"

#include "tree-pass.h"

#include "basic-block.h"

#include "flags.h"

#include "df.h"

/* Check all of the uses of pseudo variables.  If any use that is MUST

   uninitialized, add a store of 0 immediately before it.  For

   subregs, this makes combine happy.  For full word regs, this makes

   other optimizations, like the register allocator and the reg-stack

   happy as well as papers over some problems on the arm and other

   processors where certain isa constraints cannot be handled by gcc.

   These are of the form where two operands to an insn my not be the

   same.  The ra will only make them the same if they do not

   interfere, and this can only happen if one is not initialized.

   There is also the unfortunate consequence that this may mask some

   buggy programs where people forget to initialize stack variable.

   Any programmer with half a brain would look at the uninitialized

   variable warnings.  */

static void

initialize_uninitialized_regs (void)

{

  basic_block bb;

  bitmap already_genned = BITMAP_ALLOC (NULL);

  if (optimize == 1)

    {

      df_live_add_problem ();

      df_live_set_all_dirty ();

    }

  df_analyze ();

  FOR_EACH_BB (bb)

    {

      rtx insn;

      bitmap lr = DF_LR_IN (bb);

      bitmap ur = DF_LIVE_IN (bb);

      bitmap_clear (already_genned);

      FOR_BB_INSNS (bb, insn)

        {

          unsigned int uid = INSN_UID (insn);

          df_ref *use_rec;

          if (!NONDEBUG_INSN_P (insn))

            continue;

          for (use_rec = DF_INSN_UID_USES (uid); *use_rec; use_rec++)

            {

              df_ref use = *use_rec;

              unsigned int regno = DF_REF_REGNO (use);

              /* Only do this for the pseudos.  */

              if (regno < FIRST_PSEUDO_REGISTER)

                continue;

              /* Do not generate multiple moves for the same regno.

                 This is common for sequences of subreg operations.

                 They would be deleted during combine but there is no

                 reason to churn the system.  */

              if (bitmap_bit_p (already_genned, regno))

                continue;

              /* A use is MUST uninitialized if it reaches the top of

                 the block from the inside of the block (the lr test)

                 and no def for it reaches the top of the block from

                 outside of the block (the ur test).  */

              if (bitmap_bit_p (lr, regno)

                  && (!bitmap_bit_p (ur, regno)))

                {

                  rtx move_insn;

                  rtx reg = DF_REF_REAL_REG (use);

                  bitmap_set_bit (already_genned, regno);

                  start_sequence ();

                  emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));

                  move_insn = get_insns ();

                  end_sequence ();

                  emit_insn_before (move_insn, insn);

                  if (dump_file)

                    fprintf (dump_file,

                             "adding initialization in %s of reg %d at in block %d for insn %d.\n",

                             current_function_name (), regno, bb->index, uid);

                }

            }

        }

    }

  if (optimize == 1)

    {

      if (dump_file)

        df_dump (dump_file);

      df_remove_problem (df_live);

    }

  BITMAP_FREE (already_genned);

}

static bool

gate_initialize_regs (void)

{

  return optimize > 0;

}

static unsigned int

rest_of_handle_initialize_regs (void)

{

  initialize_uninitialized_regs ();

  return 0;

}

struct rtl_opt_pass pass_initialize_regs =

{

 {

  RTL_PASS,

  "init-regs",                          /* name */

  gate_initialize_regs,                 /* gate */

  rest_of_handle_initialize_regs,       /* execute */

  NULL,                                 /* sub */

  NULL,                                 /* next */

  0,                                    /* static_pass_number */

  TV_NONE,                              /* tv_id */

  0,                                    /* properties_required */

  0,                                    /* properties_provided */

  0,                                    /* properties_destroyed */

  0,                                    /* todo_flags_start */

  TODO_df_finish                        /* todo_flags_finish */

 }

};