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/* Discover if the stack pointer is modified in a function.

   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 "output.h"

#include "df.h"

/* Determine if the stack pointer is constant over the life of the function.

   Only useful before prologues have been emitted.  */

static void

notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED,

                                     void *data ATTRIBUTE_UNUSED)

{

  if (x == stack_pointer_rtx

      /* The stack pointer is only modified indirectly as the result

         of a push until later.  See the comments in rtl.texi

         regarding Embedded Side-Effects on Addresses.  */

      || (MEM_P (x)

          && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC

          && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx))

    current_function_sp_is_unchanging = 0;

}

static void

notice_stack_pointer_modification (void)

{

  basic_block bb;

  rtx insn;

  /* Assume that the stack pointer is unchanging if alloca hasn't

     been used.  */

  current_function_sp_is_unchanging = !cfun->calls_alloca;

  if (current_function_sp_is_unchanging)

    FOR_EACH_BB (bb)

      FOR_BB_INSNS (bb, insn)

        {

          if (INSN_P (insn))

            {

              /* Check if insn modifies the stack pointer.  */

              note_stores (PATTERN (insn),

                           notice_stack_pointer_modification_1,

                           NULL);

              if (! current_function_sp_is_unchanging)

                return;

            }

        }

  /* The value coming into this pass was 0, and the exit block uses

     are based on this.  If the value is now 1, we need to redo the

     exit block uses.  */

  if (df && current_function_sp_is_unchanging)

    df_update_exit_block_uses ();

}

  /* Some targets can emit simpler epilogues if they know that sp was

     not ever modified during the function.  After reload, of course,

     we've already emitted the epilogue so there's no sense searching.  */

static unsigned int

rest_of_handle_stack_ptr_mod (void)

{

  notice_stack_pointer_modification ();

  return 0;

}

struct rtl_opt_pass pass_stack_ptr_mod =

{

 {

  RTL_PASS,

  "*stack_ptr_mod",                     /* name */

  NULL,                                 /* gate */

  rest_of_handle_stack_ptr_mod,         /* 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 */

 }

};