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/* __builtin_object_size (ptr, object_size_type) computation

   Copyright (C) 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

   Contributed by Jakub Jelinek <jakub@redhat.com>

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 "diagnostic.h"

#include "tree-flow.h"

#include "tree-pass.h"

#include "tree-ssa-propagate.h"

struct object_size_info

{

  int object_size_type;

  bitmap visited, reexamine;

  int pass;

  bool changed;

  unsigned int *depths;

  unsigned int *stack, *tos;

};

static unsigned HOST_WIDE_INT unknown[4] = { -1, -1, 0, 0 };

static tree compute_object_offset (tree, tree);

static unsigned HOST_WIDE_INT addr_object_size (tree, int);

static unsigned HOST_WIDE_INT alloc_object_size (tree, int);

static tree pass_through_call (tree);

static void collect_object_sizes_for (struct object_size_info *, tree);

static void expr_object_size (struct object_size_info *, tree, tree);

static bool merge_object_sizes (struct object_size_info *, tree, tree,

                                unsigned HOST_WIDE_INT);

static bool plus_expr_object_size (struct object_size_info *, tree, tree);

static unsigned int compute_object_sizes (void);

static void init_offset_limit (void);

static void check_for_plus_in_loops (struct object_size_info *, tree);

static void check_for_plus_in_loops_1 (struct object_size_info *, tree,

                                       unsigned int);

/* object_sizes[0] is upper bound for number of bytes till the end of

   the object.

   object_sizes[1] is upper bound for number of bytes till the end of

   the subobject (innermost array or field with address taken).

   object_sizes[2] is lower bound for number of bytes till the end of

   the object and object_sizes[3] lower bound for subobject.  */

static unsigned HOST_WIDE_INT *object_sizes[4];

/* Bitmaps what object sizes have been computed already.  */

static bitmap computed[4];

/* Maximum value of offset we consider to be addition.  */

static unsigned HOST_WIDE_INT offset_limit;

/* Initialize OFFSET_LIMIT variable.  */

static void

init_offset_limit (void)

{

  if (host_integerp (TYPE_MAX_VALUE (sizetype), 1))

    offset_limit = tree_low_cst (TYPE_MAX_VALUE (sizetype), 1);

  else

    offset_limit = -1;

  offset_limit /= 2;

}

/* Compute offset of EXPR within VAR.  Return error_mark_node

   if unknown.  */

static tree

compute_object_offset (tree expr, tree var)

{

  enum tree_code code = PLUS_EXPR;

  tree base, off, t;

  if (expr == var)

    return size_zero_node;

  switch (TREE_CODE (expr))

    {

    case COMPONENT_REF:

      base = compute_object_offset (TREE_OPERAND (expr, 0), var);

      if (base == error_mark_node)

        return base;

      t = TREE_OPERAND (expr, 1);

      off = size_binop (PLUS_EXPR, DECL_FIELD_OFFSET (t),

                        size_int (tree_low_cst (DECL_FIELD_BIT_OFFSET (t), 1)

                                  / BITS_PER_UNIT));

      break;

    case REALPART_EXPR:

    case NOP_EXPR:

    case CONVERT_EXPR:

    case VIEW_CONVERT_EXPR:

    case NON_LVALUE_EXPR:

      return compute_object_offset (TREE_OPERAND (expr, 0), var);

    case IMAGPART_EXPR:

      base = compute_object_offset (TREE_OPERAND (expr, 0), var);

      if (base == error_mark_node)

        return base;

      off = TYPE_SIZE_UNIT (TREE_TYPE (expr));

      break;

    case ARRAY_REF:

      base = compute_object_offset (TREE_OPERAND (expr, 0), var);

      if (base == error_mark_node)

        return base;

      t = TREE_OPERAND (expr, 1);

      if (TREE_CODE (t) == INTEGER_CST && tree_int_cst_sgn (t) < 0)

        {

          code = MINUS_EXPR;

          t = fold_build1 (NEGATE_EXPR, TREE_TYPE (t), t);

        }

      t = fold_convert (sizetype, t);

      off = size_binop (MULT_EXPR, TYPE_SIZE_UNIT (TREE_TYPE (expr)), t);

      break;

    default:

      return error_mark_node;

    }

  return size_binop (code, base, off);

}

/* Compute __builtin_object_size for PTR, which is a ADDR_EXPR.

   OBJECT_SIZE_TYPE is the second argument from __builtin_object_size.

   If unknown, return unknown[object_size_type].  */

static unsigned HOST_WIDE_INT

addr_object_size (tree ptr, int object_size_type)

{

  tree pt_var;

  gcc_assert (TREE_CODE (ptr) == ADDR_EXPR);

  pt_var = TREE_OPERAND (ptr, 0);

  if (REFERENCE_CLASS_P (pt_var))

    pt_var = get_base_address (pt_var);

  if (pt_var

      && (SSA_VAR_P (pt_var) || TREE_CODE (pt_var) == STRING_CST)

      && TYPE_SIZE_UNIT (TREE_TYPE (pt_var))

      && host_integerp (TYPE_SIZE_UNIT (TREE_TYPE (pt_var)), 1)

      && (unsigned HOST_WIDE_INT)

         tree_low_cst (TYPE_SIZE_UNIT (TREE_TYPE (pt_var)), 1) < offset_limit)

    {

      tree bytes;

      if (pt_var != TREE_OPERAND (ptr, 0))

        {

          tree var;

          if (object_size_type & 1)

            {

              var = TREE_OPERAND (ptr, 0);

              while (var != pt_var

                      && TREE_CODE (var) != BIT_FIELD_REF

                      && TREE_CODE (var) != COMPONENT_REF

                      && TREE_CODE (var) != ARRAY_REF

                      && TREE_CODE (var) != ARRAY_RANGE_REF

                      && TREE_CODE (var) != REALPART_EXPR

                      && TREE_CODE (var) != IMAGPART_EXPR)

                var = TREE_OPERAND (var, 0);

              if (var != pt_var && TREE_CODE (var) == ARRAY_REF)

                var = TREE_OPERAND (var, 0);

              if (! TYPE_SIZE_UNIT (TREE_TYPE (var))

                  || ! host_integerp (TYPE_SIZE_UNIT (TREE_TYPE (var)), 1)

                  || tree_int_cst_lt (TYPE_SIZE_UNIT (TREE_TYPE (pt_var)),

                                      TYPE_SIZE_UNIT (TREE_TYPE (var))))

                var = pt_var;

            }

          else

            var = pt_var;

          bytes = compute_object_offset (TREE_OPERAND (ptr, 0), var);

          if (bytes != error_mark_node)

            {

              if (TREE_CODE (bytes) == INTEGER_CST

                  && tree_int_cst_lt (TYPE_SIZE_UNIT (TREE_TYPE (var)), bytes))

                bytes = size_zero_node;

              else

                bytes = size_binop (MINUS_EXPR,

                                    TYPE_SIZE_UNIT (TREE_TYPE (var)), bytes);

            }

        }

      else

        bytes = TYPE_SIZE_UNIT (TREE_TYPE (pt_var));

      if (host_integerp (bytes, 1))

        return tree_low_cst (bytes, 1);

    }

  return unknown[object_size_type];

}

/* Compute __builtin_object_size for CALL, which is a CALL_EXPR.

   Handles various allocation calls.  OBJECT_SIZE_TYPE is the second

   argument from __builtin_object_size.  If unknown, return

   unknown[object_size_type].  */

static unsigned HOST_WIDE_INT

alloc_object_size (tree call, int object_size_type)

{

  tree callee, arglist, a, bytes = NULL_TREE;

  unsigned int arg_mask = 0;

  gcc_assert (TREE_CODE (call) == CALL_EXPR);

  callee = get_callee_fndecl (call);

  arglist = TREE_OPERAND (call, 1);

  if (callee

      && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)

    switch (DECL_FUNCTION_CODE (callee))

      {

      case BUILT_IN_MALLOC:

      case BUILT_IN_ALLOCA:

        arg_mask = 1;

        break;

      /*

      case BUILT_IN_REALLOC:

        arg_mask = 2;

        break;

        */

      case BUILT_IN_CALLOC:

        arg_mask = 3;

        break;

      default:

        break;

      }

  for (a = arglist; arg_mask && a; arg_mask >>= 1, a = TREE_CHAIN (a))

    if (arg_mask & 1)

      {

        tree arg = TREE_VALUE (a);

        if (TREE_CODE (arg) != INTEGER_CST)

          break;

        if (! bytes)

          bytes = fold_convert (sizetype, arg);

        else

          bytes = size_binop (MULT_EXPR, bytes,

                              fold_convert (sizetype, arg));

      }

  if (! arg_mask && bytes && host_integerp (bytes, 1))

    return tree_low_cst (bytes, 1);

  return unknown[object_size_type];

}

/* If object size is propagated from one of function's arguments directly

   to its return value, return that argument for CALL_EXPR CALL.

   Otherwise return NULL.  */

static tree

pass_through_call (tree call)

{

  tree callee = get_callee_fndecl (call);

  tree arglist = TREE_OPERAND (call, 1);

  if (callee

      && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)

    switch (DECL_FUNCTION_CODE (callee))

      {

      case BUILT_IN_MEMCPY:

      case BUILT_IN_MEMMOVE:

      case BUILT_IN_MEMSET:

      case BUILT_IN_STRCPY:

      case BUILT_IN_STRNCPY:

      case BUILT_IN_STRCAT:

      case BUILT_IN_STRNCAT:

      case BUILT_IN_MEMCPY_CHK:

      case BUILT_IN_MEMMOVE_CHK:

      case BUILT_IN_MEMSET_CHK:

      case BUILT_IN_STRCPY_CHK:

      case BUILT_IN_STRNCPY_CHK:

      case BUILT_IN_STRCAT_CHK:

      case BUILT_IN_STRNCAT_CHK:

        if (arglist)

          return TREE_VALUE (arglist);

        break;

      default:

        break;

      }

  return NULL_TREE;

}

/* Compute __builtin_object_size value for PTR.  OBJECT_SIZE_TYPE is the

   second argument from __builtin_object_size.  */

unsigned HOST_WIDE_INT

compute_builtin_object_size (tree ptr, int object_size_type)

{

  gcc_assert (object_size_type >= 0 && object_size_type <= 3);

  if (! offset_limit)

    init_offset_limit ();

  if (TREE_CODE (ptr) == ADDR_EXPR)

    return addr_object_size (ptr, object_size_type);

  else if (TREE_CODE (ptr) == CALL_EXPR)

    {

      tree arg = pass_through_call (ptr);

      if (arg)

        return compute_builtin_object_size (arg, object_size_type);

      else

        return alloc_object_size (ptr, object_size_type);

    }

  else if (TREE_CODE (ptr) == SSA_NAME

           && POINTER_TYPE_P (TREE_TYPE (ptr))

           && object_sizes[object_size_type] != NULL)

    {

      if (!bitmap_bit_p (computed[object_size_type], SSA_NAME_VERSION (ptr)))

        {

          struct object_size_info osi;

          bitmap_iterator bi;

          unsigned int i;

          if (dump_file)

            {

              fprintf (dump_file, "Computing %s %sobject size for ",

                       (object_size_type & 2) ? "minimum" : "maximum",

                       (object_size_type & 1) ? "sub" : "");

              print_generic_expr (dump_file, ptr, dump_flags);

              fprintf (dump_file, ":\n");

            }

          osi.visited = BITMAP_ALLOC (NULL);

          osi.reexamine = BITMAP_ALLOC (NULL);

          osi.object_size_type = object_size_type;

          osi.depths = NULL;

          osi.stack = NULL;

          osi.tos = NULL;

          /* First pass: walk UD chains, compute object sizes that

             can be computed.  osi.reexamine bitmap at the end will

             contain what variables were found in dependency cycles

             and therefore need to be reexamined.  */

          osi.pass = 0;

          osi.changed = false;

          collect_object_sizes_for (&osi, ptr);

          /* Second pass: keep recomputing object sizes of variables

             that need reexamination, until no object sizes are

             increased or all object sizes are computed.  */

          if (! bitmap_empty_p (osi.reexamine))

            {

              bitmap reexamine = BITMAP_ALLOC (NULL);

              /* If looking for minimum instead of maximum object size,

                 detect cases where a pointer is increased in a loop.

                 Although even without this detection pass 2 would eventually

                 terminate, it could take a long time.  If a pointer is

                 increasing this way, we need to assume 0 object size.

                 E.g. p = &buf[0]; while (cond) p = p + 4;  */

              if (object_size_type & 2)

                {

                  osi.depths = XCNEWVEC (unsigned int, num_ssa_names);

                  osi.stack = XNEWVEC (unsigned int, num_ssa_names);

                  osi.tos = osi.stack;

                  osi.pass = 1;

                  /* collect_object_sizes_for is changing

                     osi.reexamine bitmap, so iterate over a copy.  */

                  bitmap_copy (reexamine, osi.reexamine);

                  EXECUTE_IF_SET_IN_BITMAP (reexamine, 0, i, bi)

                    if (bitmap_bit_p (osi.reexamine, i))

                      check_for_plus_in_loops (&osi, ssa_name (i));

                  free (osi.depths);

                  osi.depths = NULL;

                  free (osi.stack);

                  osi.stack = NULL;

                  osi.tos = NULL;

                }

              do

                {

                  osi.pass = 2;

                  osi.changed = false;

                  /* collect_object_sizes_for is changing

                     osi.reexamine bitmap, so iterate over a copy.  */

                  bitmap_copy (reexamine, osi.reexamine);

                  EXECUTE_IF_SET_IN_BITMAP (reexamine, 0, i, bi)

                    if (bitmap_bit_p (osi.reexamine, i))

                      {

                        collect_object_sizes_for (&osi, ssa_name (i));

                        if (dump_file && (dump_flags & TDF_DETAILS))

                          {

                            fprintf (dump_file, "Reexamining ");

                            print_generic_expr (dump_file, ssa_name (i),

                                                dump_flags);

                            fprintf (dump_file, "\n");

                          }

                      }

                }

              while (osi.changed);

              BITMAP_FREE (reexamine);

            }

          EXECUTE_IF_SET_IN_BITMAP (osi.reexamine, 0, i, bi)

            bitmap_set_bit (computed[object_size_type], i);

          /* Debugging dumps.  */

          if (dump_file)

            {

              EXECUTE_IF_SET_IN_BITMAP (osi.visited, 0, i, bi)

                if (object_sizes[object_size_type][i]

                    != unknown[object_size_type])

                  {

                    print_generic_expr (dump_file, ssa_name (i),

                                        dump_flags);

                    fprintf (dump_file,

                             ": %s %sobject size "

                             HOST_WIDE_INT_PRINT_UNSIGNED "\n",

                             (object_size_type & 2) ? "minimum" : "maximum",

                             (object_size_type & 1) ? "sub" : "",

                             object_sizes[object_size_type][i]);

                  }

            }

          BITMAP_FREE (osi.reexamine);

          BITMAP_FREE (osi.visited);

        }

      return object_sizes[object_size_type][SSA_NAME_VERSION (ptr)];

    }

  return unknown[object_size_type];

}

/* Compute object_sizes for PTR, defined to VALUE, which is not

   a SSA_NAME.  */

static void

expr_object_size (struct object_size_info *osi, tree ptr, tree value)

{

  int object_size_type = osi->object_size_type;

  unsigned int varno = SSA_NAME_VERSION (ptr);

  unsigned HOST_WIDE_INT bytes;

  gcc_assert (object_sizes[object_size_type][varno]

              != unknown[object_size_type]);

  gcc_assert (osi->pass == 0);

  if (TREE_CODE (value) == WITH_SIZE_EXPR)

    value = TREE_OPERAND (value, 0);

  /* Pointer variables should have been handled by merge_object_sizes.  */

  gcc_assert (TREE_CODE (value) != SSA_NAME

              || !POINTER_TYPE_P (TREE_TYPE (value)));

  if (TREE_CODE (value) == ADDR_EXPR)

    bytes = addr_object_size (value, object_size_type);

  else if (TREE_CODE (value) == CALL_EXPR)

    bytes = alloc_object_size (value, object_size_type);

  else

    bytes = unknown[object_size_type];

  if ((object_size_type & 2) == 0)

    {

      if (object_sizes[object_size_type][varno] < bytes)

        object_sizes[object_size_type][varno] = bytes;

    }

  else

    {

      if (object_sizes[object_size_type][varno] > bytes)

        object_sizes[object_size_type][varno] = bytes;

    }

}

/* Merge object sizes of ORIG + OFFSET into DEST.  Return true if

   the object size might need reexamination later.  */

static bool

merge_object_sizes (struct object_size_info *osi, tree dest, tree orig,

                    unsigned HOST_WIDE_INT offset)

{

  int object_size_type = osi->object_size_type;

  unsigned int varno = SSA_NAME_VERSION (dest);

  unsigned HOST_WIDE_INT orig_bytes;

  if (object_sizes[object_size_type][varno] == unknown[object_size_type])

    return false;

  if (offset >= offset_limit)

    {

      object_sizes[object_size_type][varno] = unknown[object_size_type];

      return false;

    }

  if (osi->pass == 0)

    collect_object_sizes_for (osi, orig);

  orig_bytes = object_sizes[object_size_type][SSA_NAME_VERSION (orig)];

  if (orig_bytes != unknown[object_size_type])

    orig_bytes = (offset > orig_bytes)

                 ? (unsigned HOST_WIDE_INT) 0 : orig_bytes - offset;

  if ((object_size_type & 2) == 0)

    {

      if (object_sizes[object_size_type][varno] < orig_bytes)

        {

          object_sizes[object_size_type][varno] = orig_bytes;

          osi->changed = true;

        }

    }

  else

    {

      if (object_sizes[object_size_type][varno] > orig_bytes)

        {

          object_sizes[object_size_type][varno] = orig_bytes;

          osi->changed = true;

        }

    }

  return bitmap_bit_p (osi->reexamine, SSA_NAME_VERSION (orig));

}

/* Compute object_sizes for PTR, defined to VALUE, which is

   a PLUS_EXPR.  Return true if the object size might need reexamination

   later.  */

static bool

plus_expr_object_size (struct object_size_info *osi, tree var, tree value)

{

  tree op0 = TREE_OPERAND (value, 0);

  tree op1 = TREE_OPERAND (value, 1);

  bool ptr1_p = POINTER_TYPE_P (TREE_TYPE (op0))

                && TREE_CODE (op0) != INTEGER_CST;

  bool ptr2_p = POINTER_TYPE_P (TREE_TYPE (op1))

                && TREE_CODE (op1) != INTEGER_CST;

  int object_size_type = osi->object_size_type;

  unsigned int varno = SSA_NAME_VERSION (var);

  unsigned HOST_WIDE_INT bytes;

  gcc_assert (TREE_CODE (value) == PLUS_EXPR);

  if (object_sizes[object_size_type][varno] == unknown[object_size_type])

    return false;

  /* Swap operands if needed.  */

  if (ptr2_p && !ptr1_p)

    {

      tree tem = op0;

      op0 = op1;

      op1 = tem;

      ptr1_p = true;

      ptr2_p = false;

    }

  /* Handle PTR + OFFSET here.  */

  if (ptr1_p

      && !ptr2_p

      && TREE_CODE (op1) == INTEGER_CST

      && (TREE_CODE (op0) == SSA_NAME

          || TREE_CODE (op0) == ADDR_EXPR))

    {

      if (! host_integerp (op1, 1))

        bytes = unknown[object_size_type];

      else if (TREE_CODE (op0) == SSA_NAME)

        return merge_object_sizes (osi, var, op0, tree_low_cst (op1, 1));

      else

        {

          unsigned HOST_WIDE_INT off = tree_low_cst (op1, 1);

          bytes = compute_builtin_object_size (op0, object_size_type);

          if (off > offset_limit)

            bytes = unknown[object_size_type];

          else if (off > bytes)

            bytes = 0;

          else

            bytes -= off;

        }

    }

  else

    bytes = unknown[object_size_type];

  if ((object_size_type & 2) == 0)

    {

      if (object_sizes[object_size_type][varno] < bytes)

        object_sizes[object_size_type][varno] = bytes;

    }

  else

    {

      if (object_sizes[object_size_type][varno] > bytes)

        object_sizes[object_size_type][varno] = bytes;

    }

  return false;

}

/* Compute object sizes for VAR.

   For ADDR_EXPR an object size is the number of remaining bytes

   to the end of the object (where what is considered an object depends on

   OSI->object_size_type).

   For allocation CALL_EXPR like malloc or calloc object size is the size

   of the allocation.

   For pointer PLUS_EXPR where second operand is a constant integer,

   object size is object size of the first operand minus the constant.

   If the constant is bigger than the number of remaining bytes until the

   end of the object, object size is 0, but if it is instead a pointer

   subtraction, object size is unknown[object_size_type].

   To differentiate addition from subtraction, ADDR_EXPR returns

   unknown[object_size_type] for all objects bigger than half of the address

   space, and constants less than half of the address space are considered

   addition, while bigger constants subtraction.

   For a memcpy like CALL_EXPR that always returns one of its arguments, the

   object size is object size of that argument.

   Otherwise, object size is the maximum of object sizes of variables

   that it might be set to.  */

static void

collect_object_sizes_for (struct object_size_info *osi, tree var)

{

  int object_size_type = osi->object_size_type;

  unsigned int varno = SSA_NAME_VERSION (var);

  tree stmt;

  bool reexamine;

  if (bitmap_bit_p (computed[object_size_type], varno))

    return;

  if (osi->pass == 0)

    {

      if (! bitmap_bit_p (osi->visited, varno))

        {

          bitmap_set_bit (osi->visited, varno);

          object_sizes[object_size_type][varno]

            = (object_size_type & 2) ? -1 : 0;

        }

      else

        {

          /* Found a dependency loop.  Mark the variable for later

             re-examination.  */

          bitmap_set_bit (osi->reexamine, varno);

          if (dump_file && (dump_flags & TDF_DETAILS))

            {

              fprintf (dump_file, "Found a dependency loop at ");

              print_generic_expr (dump_file, var, dump_flags);

              fprintf (dump_file, "\n");