Re: [[GCC13][Patch][V3] 1/2] Add a new option -fstrict-flex-array[=n] and new attribute strict_flex_array

[Richard Biener <rguenther@suse.de>]

On Wed, 17 Aug 2022, Qing Zhao wrote:

> Add the following new option -fstrict-flex-array[=n] and a corresponding
> attribute strict_flex_array to GCC:
> 
> '-fstrict-flex-array'
>      Treat the trailing array of a structure as a flexible array member
>      in a stricter way.  The positive form is equivalent to
>      '-fstrict-flex-array=3', which is the strictest.  A trailing array
>      is treated as a flexible array member only when it is declared as a
>      flexible array member per C99 standard onwards.  The negative form
>      is equivalent to '-fstrict-flex-array=0', which is the least
>      strict.  All trailing arrays of structures are treated as flexible
>      array members.
> 
> '-fstrict-flex-array=LEVEL'
>      Treat the trailing array of a structure as a flexible array member
>      in a stricter way.  The value of LEVEL controls the level of
>      strictness.
> 
>      The possible values of LEVEL are the same as for the
>      'strict_flex_array' attribute (*note Variable Attributes::).
> 
>      You can control this behavior for a specific trailing array field
>      of a structure by using the variable attribute 'strict_flex_array'
>      attribute (*note Variable Attributes::).
> 
>      This option is only valid when flexible array member is supported in the
>      language. FOR ISO C before C99 and ISO C++, no language support for the flexible
>      array member at all, this option will be invalid and a warning will be issued.
>      When -std=gnu89 is specified or C++ with GNU extension, only zero-length array
>      extension and one-size array are supported, as a result, LEVEL=3 will be
>      invalid and a warning will be issued.
> 
> 'strict_flex_array (LEVEL)'
>      The 'strict_flex_array' attribute should be attached to the
>      trailing array field of a structure.  It specifies the level of
>      strictness of treating the trailing array field of a structure as a
>      flexible array member.  LEVEL must be an integer betwen 0 to 3.
> 
>      LEVEL=0 is the least strict level, all trailing arrays of
>      structures are treated as flexible array members.  LEVEL=3 is the
>      strictest level, only when the trailing array is declared as a
>      flexible array member per C99 standard onwards ([]), it is treated
>      as a flexible array member.
> 
>      There are two more levels in between 0 and 3, which are provided to
>      support older codes that use GCC zero-length array extension ([0])
>      or one-size array as flexible array member ([1]): When LEVEL is 1,
>      the trailing array is treated as a flexible array member when it is
>      declared as either [], [0], or [1]; When LEVEL is 2, the trailing
>      array is treated as a flexible array member when it is declared as
>      either [], or [0].
> 
>      This attribute can be used with or without '-fstrict-flex-array'.
>      When both the attribute and the option present at the same time,
>      the level of the strictness for the specific trailing array field
>      is determined by the attribute.
> 
>      This attribute is only valid when flexible array member is supported in the
>      language. For ISO C before C99 and ISO C++, no language support for the flexible
>      array member at all, this attribute will be invalid and a warning is issued.
>      When -std=gnu89 is specified or C++ with GNU extension, only zero-length array
>      extension and one-size array are supported, as a result, LEVEL=3 will be
>      invalid and a warning is issued.
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-attribs.cc (handle_strict_flex_arrays_attribute): New function.
> 	(c_common_attribute_table): New item for strict_flex_array.
> 	* c-opts.cc (c_common_post_options): Handle the combination of
> 	-fstrict-flex-arrays and -std specially.
> 	* c.opt: (fstrict-flex-array): New option.
> 	(fstrict-flex-array=): New option.
> 
> gcc/c/ChangeLog:
> 
> 	* c-decl.cc (flexible_array_member_type_p): New function.
> 	(one_element_array_type_p): Likewise.
> 	(zero_length_array_type_p): Likewise.
> 	(add_flexible_array_elts_to_size): Call new utility
> 	routine flexible_array_member_type_p.
> 	(is_flexible_array_member_p): New function.
> 	(finish_struct): Set the new DECL_NOT_FLEXARRAY flag.
> 
> gcc/cp/ChangeLog:
> 
> 	* module.cc (trees_out::core_bools): Stream out new bit
> 	decl_not_flexarray.
> 	(trees_in::core_bools): Stream in new bit decl_not_flexarray.
> 
> gcc/ChangeLog:
> 
> 	* doc/extend.texi: Document strict_flex_array attribute.
> 	* doc/invoke.texi: Document -fstrict-flex-array[=n] option.
> 	* print-tree.cc (print_node): Print new bit decl_not_flexarray.
> 	* tree-core.h (struct tree_decl_common): New bit field
> 	decl_not_flexarray.
> 	* tree-streamer-in.cc (unpack_ts_decl_common_value_fields): Stream
> 	in new bit decl_not_flexarray.
> 	* tree-streamer-out.cc (pack_ts_decl_common_value_fields): Stream
> 	out new bit decl_not_flexarray.
> 	* tree.cc (array_at_struct_end_p): Update it with the new bit field
> 	decl_not_flexarray.
> 	* tree.h (DECL_NOT_FLEXARRAY): New fla

The middle-end changes are OK, the c/ and cp/ changes need review
from a frontend maintainer.

Are the testcases actually C/C++ code?  You can use
testsuite/c-c++-common/ to place tests that run with both frontends.

Richard.

> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/strict-flex-array-1.C: New test.
> 	* g++.dg/strict-flex-array-2.C: New test.
> 	* g++.dg/strict-flex-array-3.C: New test.
> 	* g++.dg/strict-flex-array-4.C: New test.
> 	* gcc.dg/strict-flex-array-1.c: New test.
> 	* gcc.dg/strict-flex-array-2.c: New test.
> 	* gcc.dg/strict-flex-array-3.c: New test.
> 	* gcc.dg/strict-flex-array-4.c: New test.
> ---
>  gcc/c-family/c-attribs.cc                  |  94 +++++++++++++++
>  gcc/c-family/c-opts.cc                     |  41 +++++++
>  gcc/c-family/c.opt                         |   7 ++
>  gcc/c/c-decl.cc                            | 130 +++++++++++++++++++--
>  gcc/cp/module.cc                           |   2 +
>  gcc/doc/extend.texi                        |  33 ++++++
>  gcc/doc/invoke.texi                        |  34 +++++-
>  gcc/print-tree.cc                          |   8 +-
>  gcc/testsuite/g++.dg/strict-flex-array-1.C |  31 +++++
>  gcc/testsuite/g++.dg/strict-flex-array-2.C |  16 +++
>  gcc/testsuite/g++.dg/strict-flex-array-3.C |  21 ++++
>  gcc/testsuite/g++.dg/strict-flex-array-4.C |   9 ++
>  gcc/testsuite/gcc.dg/strict-flex-array-1.c |  31 +++++
>  gcc/testsuite/gcc.dg/strict-flex-array-2.c |  15 +++
>  gcc/testsuite/gcc.dg/strict-flex-array-3.c |  21 ++++
>  gcc/testsuite/gcc.dg/strict-flex-array-4.c |  10 ++
>  gcc/tree-core.h                            |   5 +-
>  gcc/tree-streamer-in.cc                    |   1 +
>  gcc/tree-streamer-out.cc                   |   1 +
>  gcc/tree.cc                                |  45 +++++--
>  gcc/tree.h                                 |  14 ++-
>  21 files changed, 541 insertions(+), 28 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-1.C
>  create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-2.C
>  create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-3.C
>  create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-4.C
>  create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-1.c
>  create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-2.c
>  create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-3.c
>  create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-4.c
> 
> diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
> index e4f1d3542f37..9c9927cefa0d 100644
> --- a/gcc/c-family/c-attribs.cc
> +++ b/gcc/c-family/c-attribs.cc
> @@ -101,6 +101,8 @@ static tree handle_special_var_sec_attribute (tree *, tree, tree, int, bool *);
>  static tree handle_aligned_attribute (tree *, tree, tree, int, bool *);
>  static tree handle_warn_if_not_aligned_attribute (tree *, tree, tree,
>  						  int, bool *);
> +static tree handle_strict_flex_arrays_attribute (tree *, tree, tree,
> +						 int, bool *);
>  static tree handle_weak_attribute (tree *, tree, tree, int, bool *) ;
>  static tree handle_noplt_attribute (tree *, tree, tree, int, bool *) ;
>  static tree handle_alias_ifunc_attribute (bool, tree *, tree, tree, bool *);
> @@ -368,6 +370,8 @@ const struct attribute_spec c_common_attribute_table[] =
>  	                      attr_aligned_exclusions },
>    { "warn_if_not_aligned",    0, 1, false, false, false, false,
>  			      handle_warn_if_not_aligned_attribute, NULL },
> +  { "strict_flex_arrays",      1, 1, false, false, false, false,
> +			      handle_strict_flex_arrays_attribute, NULL },
>    { "weak",                   0, 0, true,  false, false, false,
>  			      handle_weak_attribute, NULL },
>    { "noplt",                   0, 0, true,  false, false, false,
> @@ -2505,6 +2509,96 @@ handle_warn_if_not_aligned_attribute (tree *node, tree name,
>  					  no_add_attrs, true);
>  }
>  
> +/* Handle a "strict_flex_arrays" attribute; arguments as in
> +   struct attribute_spec.handler.  */
> +
> +static tree
> +handle_strict_flex_arrays_attribute (tree *node, tree name,
> +				     tree args, int ARG_UNUSED (flags),
> +				     bool *no_add_attrs)
> +{
> +  tree decl = *node;
> +  tree argval = TREE_VALUE (args);
> +
> +  /* This attribute only applies to field decls of a structure.  */
> +  if (TREE_CODE (decl) != FIELD_DECL)
> +    {
> +      error_at (DECL_SOURCE_LOCATION (decl),
> +		"%qE attribute may not be specified for %q+D", name, decl);
> +      *no_add_attrs = true;
> +    }
> +  /* This attribute only applies to field with array type.  */
> +  else if (TREE_CODE (TREE_TYPE (decl)) != ARRAY_TYPE)
> +    {
> +      error_at (DECL_SOURCE_LOCATION (decl),
> +		"%qE attribute may not be specified for a non array field",
> +		name);
> +      *no_add_attrs = true;
> +    }
> +  else if (TREE_CODE (argval) != INTEGER_CST)
> +    {
> +      error_at (DECL_SOURCE_LOCATION (decl),
> +		"%qE attribute argument not an integer", name);
> +      *no_add_attrs = true;
> +    }
> +  else if (!tree_fits_uhwi_p (argval) || tree_to_uhwi (argval) > 3)
> +    {
> +      error_at (DECL_SOURCE_LOCATION (decl),
> +		"%qE attribute argument %qE is not an integer constant"
> +		" between 0 and 3", name, argval);
> +      *no_add_attrs = true;
> +    }
> +  else
> +    {
> +      unsigned int level = tree_to_uhwi (argval);
> +      /* check whether the attribute is valid based on language standard.
> +	 the attribute is only valid when flexible array member is
> +	 supported in the language. Therefore, we should invalid this attribute or
> +	 specific level of this attribute for the following situations:
> +	A. When -std=c89 is specified, no language support at all, invalid this
> +	   attribute and issue a warning;
> +	B. When -std=gnu89 is specified, only zero-length array extension and
> +	   one-size array are supported, level=3 will be invalid and a warning
> +	   will be issued.
> +	C. C++ without GNU extension, no language support at all, invalid this
> +	   attribute and issue a warning;
> +	D. C++ with GNU extension, only zero-length array extension and one-size
> +	   array are supported, level=3 will be invalid and a warning will be
> +	   issued.  */
> +      if (level > 0)
> +	{
> +	  if (!c_dialect_cxx () && flag_iso && flag_isoc99 == 0)
> +	  {
> +	    warning (OPT_Wattributes, "%qE attribute ignored since it is "
> +		     "not supported with a ISO C before C99", name);
> +	    *no_add_attrs = true;
> +	  }
> +	  else if (!c_dialect_cxx () && !flag_iso
> +		   && flag_isoc99 == 0 && level == 3)
> +	  {
> +	    warning (OPT_Wattributes, "%qE = 3 attribute ignored since it is "
> +		     "not supported with a GNU extension GNU89", name);
> +	    *no_add_attrs = true;
> +	  }
> +	  else if (c_dialect_cxx () && flag_iso)
> +	  {
> +	    warning (OPT_Wattributes, "%qE attribute ignored since it is "
> +		     "not supported with a ISO C++", name);
> +	    *no_add_attrs = true;
> +	  }
> +	  else if (c_dialect_cxx () && !flag_iso
> +		   && level == 3)
> +	  {
> +	    warning (OPT_Wattributes, "%qE = 3 attribute ignored since it is "
> +		     "not supported for C++ with GNU extension", name);
> +	    *no_add_attrs = true;
> +	  }
> +	}
> +      }
> +
> +  return NULL_TREE;
> +}
> +
>  /* Handle a "weak" attribute; arguments as in
>     struct attribute_spec.handler.  */
>  
> diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
> index 4e1463689de3..639eb40f3c86 100644
> --- a/gcc/c-family/c-opts.cc
> +++ b/gcc/c-family/c-opts.cc
> @@ -870,6 +870,47 @@ c_common_post_options (const char **pfilename)
>      SET_OPTION_IF_UNSET (&global_options, &global_options_set,
>  			 flag_tree_loop_distribute_patterns, 0);
>  
> +  /* -fstrict-flex-arrays is only valid when flexible array member is
> +     supported in the language. Therefore, we should invalid this option or
> +     specific level of this option for the following situations:
> +     A. When -std=c89 is specified, no language support at all, invalid this
> +	option and issue a warning;
> +     B. When -std=gnu89 is specified, only zero-length array extension and
> +	one-size array are supported, level=3 will be invalid and a warning
> +	will be issued.
> +     C. C++ without GNU extension, no language support at all, invalid this
> +	option and issue a warning;
> +     D. C++ with GNU extension, only zero-length array extension and one-size
> +	array are supported, level=3 will be invalid and a warning will be
> +	issued.  */
> +  if (flag_strict_flex_arrays > 0)
> +    {
> +      if (!c_dialect_cxx () && flag_iso && flag_isoc99 == 0)
> +	{
> +	  flag_strict_flex_arrays = 0;
> +	  warning (0, "%<-fstrict-flex-arrays%> is not supported with a ISO C "
> +		   "before C99, ignored");
> +	}
> +      else if (!c_dialect_cxx () && !flag_iso && flag_isoc99 == 0 && flag_strict_flex_arrays == 3)
> +	{
> +	  flag_strict_flex_arrays = 0;
> +	  warning (0, "%<-fstrict-flex-arrays=3%> is not supported with a "
> +		   "GNU extension GNU89, ignored");
> +	}
> +      else if (c_dialect_cxx () && flag_iso)
> +	{
> +	  flag_strict_flex_arrays = 0;
> +	  warning (0, "%<-fstrict-flex-arrays%> is not supported with a ISO "
> +		   "C++, ignored");
> +	}
> +      else if (c_dialect_cxx () && !flag_iso && flag_strict_flex_arrays == 3)
> +	{
> +	  flag_strict_flex_arrays = 0;
> +	  warning (0, "%<-fstrict-flex-arrays=3%> is not supported for C++ "
> +		   "with GNU extension, ignored");
> +	}
> +    }
> +
>    /* -Woverlength-strings is off by default, but is enabled by -Wpedantic.
>       It is never enabled in C++, as the minimum limit is not normative
>       in that standard.  */
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 44e1a60ce246..1e944f8a3055 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -2060,6 +2060,13 @@ fsized-deallocation
>  C++ ObjC++ Var(flag_sized_deallocation) Init(-1)
>  Enable C++14 sized deallocation support.
>  
> +fstrict-flex-arrays
> +C C++ Common Alias(fstrict-flex-arrays=,3,0)
> +
> +fstrict-flex-arrays=
> +C C++ Common Joined RejectNegative UInteger Var(flag_strict_flex_arrays) Init(0) IntegerRange(0,3)
> +-fstrict-flex-arrays=<level>    Treat the trailing array of a structure as a flexible array in a stricter way.  The default is treating all trailing arrays of structures as flexible arrays.
> +
>  fsquangle
>  C++ ObjC++ WarnRemoved
>  
> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
> index ae8990c138fd..a2e125d4ddd5 100644
> --- a/gcc/c/c-decl.cc
> +++ b/gcc/c/c-decl.cc
> @@ -4999,6 +4999,41 @@ set_array_declarator_inner (struct c_declarator *decl,
>    return decl;
>  }
>  
> +/* Determine whether TYPE is a ISO C99 flexible array memeber type "[]".  */
> +static bool
> +flexible_array_member_type_p (const_tree type)
> +{
> +  if (TREE_CODE (type) == ARRAY_TYPE
> +      && TYPE_SIZE (type) == NULL_TREE
> +      && TYPE_DOMAIN (type) != NULL_TREE
> +      && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
> +    return true;
> +
> +  return false;
> +}
> +
> +/* Determine whether TYPE is a one-element array type "[1]".  */
> +static bool
> +one_element_array_type_p (const_tree type)
> +{
> +  if (TREE_CODE (type) != ARRAY_TYPE)
> +    return false;
> +  return integer_zerop (array_type_nelts (type));
> +}
> +
> +/* Determine whether TYPE is a zero-length array type "[0]".  */
> +static bool
> +zero_length_array_type_p (const_tree type)
> +{
> +  if (TREE_CODE (type) == ARRAY_TYPE)
> +    if (tree type_size = TYPE_SIZE_UNIT (type))
> +      if ((integer_zerop (type_size))
> +	   && TYPE_DOMAIN (type) != NULL_TREE
> +	   && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
> +	return true;
> +  return false;
> +}
> +
>  /* INIT is a constructor that forms DECL's initializer.  If the final
>     element initializes a flexible array field, add the size of that
>     initializer to DECL's size.  */
> @@ -5013,10 +5048,7 @@ add_flexible_array_elts_to_size (tree decl, tree init)
>  
>    elt = CONSTRUCTOR_ELTS (init)->last ().value;
>    type = TREE_TYPE (elt);
> -  if (TREE_CODE (type) == ARRAY_TYPE
> -      && TYPE_SIZE (type) == NULL_TREE
> -      && TYPE_DOMAIN (type) != NULL_TREE
> -      && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
> +  if (flexible_array_member_type_p (type))
>      {
>        complete_array_type (&type, elt, false);
>        DECL_SIZE (decl)
> @@ -8720,6 +8752,81 @@ finish_incomplete_vars (tree incomplete_vars, bool toplevel)
>      }
>  }
>  
> +
> +/* Determine whether the FIELD_DECL X is a flexible array member according to
> +   the following info:
> +  A. whether the FIELD_DECL X is the last field of the DECL_CONTEXT;
> +  B. whether the FIELD_DECL is an array that is declared as "[]", "[0]",
> +     or "[1]";
> +  C. flag_strict_flex_arrays;
> +  D. the attribute strict_flex_array that is attached to the field
> +     if presenting.
> +  Return TRUE when it's a flexible array member, FALSE otherwise.  */
> +
> +static bool
> +is_flexible_array_member_p (bool is_last_field,
> +			    tree x)
> +{
> +  /* if not the last field, return false.  */
> +  if (!is_last_field)
> +    return false;
> +
> +  /* if not an array field, return false.  */
> +  if (TREE_CODE (TREE_TYPE (x)) != ARRAY_TYPE)
> +    return false;
> +
> +  bool is_zero_length_array = zero_length_array_type_p (TREE_TYPE (x));
> +  bool is_one_element_array = one_element_array_type_p (TREE_TYPE (x));
> +  bool is_flexible_array = flexible_array_member_type_p (TREE_TYPE (x));
> +
> +  unsigned int strict_flex_array_level = flag_strict_flex_arrays;
> +
> +  tree attr_strict_flex_array = lookup_attribute ("strict_flex_arrays",
> +						  DECL_ATTRIBUTES (x));
> +  /* if there is a strict_flex_array attribute attached to the field,
> +     override the flag_strict_flex_arrays.  */
> +  if (attr_strict_flex_array)
> +    {
> +      /* get the value of the level first from the attribute.  */
> +      unsigned HOST_WIDE_INT attr_strict_flex_array_level = 0;
> +      gcc_assert (TREE_VALUE (attr_strict_flex_array) != NULL_TREE);
> +      attr_strict_flex_array = TREE_VALUE (attr_strict_flex_array);
> +      gcc_assert (TREE_VALUE (attr_strict_flex_array) != NULL_TREE);
> +      attr_strict_flex_array = TREE_VALUE (attr_strict_flex_array);
> +      gcc_assert (tree_fits_uhwi_p (attr_strict_flex_array));
> +      attr_strict_flex_array_level = tree_to_uhwi (attr_strict_flex_array);
> +
> +      /* the attribute has higher priority than flag_struct_flex_array.  */
> +      strict_flex_array_level = attr_strict_flex_array_level;
> +    }
> +
> +  switch (strict_flex_array_level)
> +    {
> +      case 0:
> +	/* default, all trailing arrays are flexiable array members.  */
> +	return true;
> +      case 1:
> +	/* Level 1: all "[1]", "[0]", and "[]" are flexiable array members.  */
> +	if (is_one_element_array)
> +	  return true;
> +	/* FALLTHROUGH.  */
> +      case 2:
> +	/* Level 2: all "[0]", and "[]" are flexiable array members.  */
> +	if (is_zero_length_array)
> +	  return true;
> +	/* FALLTHROUGH.  */
> +      case 3:
> +	/* Level 3: Only "[]" are flexible array members.  */
> +	if (is_flexible_array)
> +	  return true;
> +	break;
> +      default:
> +	gcc_unreachable ();
> +    }
> +  return false;
> +}
> +
> +
>  /* Fill in the fields of a RECORD_TYPE or UNION_TYPE node, T.
>     LOC is the location of the RECORD_TYPE or UNION_TYPE's definition.
>     FIELDLIST is a chain of FIELD_DECL nodes for the fields.
> @@ -8781,6 +8888,11 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
>    bool saw_named_field = false;
>    for (x = fieldlist; x; x = DECL_CHAIN (x))
>      {
> +      /* whether this field is the last field of the structure or union.
> +	 for UNION, any field is the last field of it.  */
> +      bool is_last_field = (DECL_CHAIN (x) == NULL_TREE)
> +			    || (TREE_CODE (t) == UNION_TYPE);
> +
>        if (TREE_TYPE (x) == error_mark_node)
>  	continue;
>  
> @@ -8819,10 +8931,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
>  	DECL_PACKED (x) = 1;
>  
>        /* Detect flexible array member in an invalid context.  */
> -      if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE
> -	  && TYPE_SIZE (TREE_TYPE (x)) == NULL_TREE
> -	  && TYPE_DOMAIN (TREE_TYPE (x)) != NULL_TREE
> -	  && TYPE_MAX_VALUE (TYPE_DOMAIN (TREE_TYPE (x))) == NULL_TREE)
> +      if (flexible_array_member_type_p (TREE_TYPE (x)))
>  	{
>  	  if (TREE_CODE (t) == UNION_TYPE)
>  	    {
> @@ -8830,7 +8939,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
>  			"flexible array member in union");
>  	      TREE_TYPE (x) = error_mark_node;
>  	    }
> -	  else if (DECL_CHAIN (x) != NULL_TREE)
> +	  else if (!is_last_field)
>  	    {
>  	      error_at (DECL_SOURCE_LOCATION (x),
>  			"flexible array member not at end of struct");
> @@ -8850,6 +8959,9 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
>  	pedwarn (DECL_SOURCE_LOCATION (x), OPT_Wpedantic,
>  		 "invalid use of structure with flexible array member");
>  
> +      /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x.  */
> +      DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p (is_last_field, x);
> +
>        if (DECL_NAME (x)
>  	  || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
>  	saw_named_field = true;
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index f27f4d091e5e..75ee2514f66b 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -5414,6 +5414,7 @@ trees_out::core_bools (tree t)
>        WB (t->decl_common.decl_by_reference_flag);
>        WB (t->decl_common.decl_read_flag);
>        WB (t->decl_common.decl_nonshareable_flag);
> +      WB (t->decl_common.decl_not_flexarray);
>      }
>  
>    if (CODE_CONTAINS_STRUCT (code, TS_DECL_WITH_VIS))
> @@ -5558,6 +5559,7 @@ trees_in::core_bools (tree t)
>        RB (t->decl_common.decl_by_reference_flag);
>        RB (t->decl_common.decl_read_flag);
>        RB (t->decl_common.decl_nonshareable_flag);
> +      RB (t->decl_common.decl_not_flexarray);
>      }
>  
>    if (CODE_CONTAINS_STRUCT (code, TS_DECL_WITH_VIS))
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 7fe7f8817cdd..99b43ed3852c 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -7473,6 +7473,39 @@ This warning can be disabled by @option{-Wno-if-not-aligned}.
>  The @code{warn_if_not_aligned} attribute can also be used for types
>  (@pxref{Common Type Attributes}.)
>  
> +@cindex @code{strict_flex_arrays} variable attribute
> +@item strict_flex_arrays (@var{level})
> +The @code{strict_flex_arrays} attribute should be attached to the trailing
> +array field of a structure.  It specifies the level of strictness of
> +treating the trailing array field of a structure as a flexible array
> +member. @var{level} must be an integer betwen 0 to 3.
> +
> +@var{level}=0 is the least strict level, all trailing arrays of structures
> +are treated as flexible array members. @var{level}=3 is the strictest level,
> +only when the trailing array is declared as a flexible array member per C99
> +standard onwards ([]), it is treated as a flexible array member.
> +
> +There are two more levels in between 0 and 3, which are provided to support
> +older codes that use GCC zero-length array extension ([0]) or one-size array
> +as flexible array member ([1]):
> +When @var{level} is 1, the trailing array is treated as a flexible array member
> +when it is declared as either "[]", "[0]", or "[1]";
> +When @var{level} is 2, the trailing array is treated as a flexible array member
> +when it is declared as either "[]", or "[0]".
> +
> +This attribute can be used with or without the @option{-fstrict-flex-arrays}.
> +When both the attribute and the option present at the same time, the level of
> +the strictness for the specific trailing array field is determined by the
> +attribute.
> +
> +This attribute is only valid when flexible array member is supported in the
> +language. For ISO C before C99 and ISO C++, no language support for the flexible
> +array member at all, this attribute will be invalid and a warning is issued.
> +When -std=gnu89 is specified or C++ with GNU extension, only zero-length array
> +extension and one-size array are supported, as a result, @var{level}=3 will be
> +invalid and a warning is issued.
> +
> +
>  @item alloc_size (@var{position})
>  @itemx alloc_size (@var{position-1}, @var{position-2})
>  @cindex @code{alloc_size} variable attribute
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 863580b3710a..2a0a3cf3de10 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -207,7 +207,8 @@ in the following sections.
>  -fopenmp  -fopenmp-simd @gol
>  -fpermitted-flt-eval-methods=@var{standard} @gol
>  -fplan9-extensions  -fsigned-bitfields  -funsigned-bitfields @gol
> --fsigned-char  -funsigned-char  -fsso-struct=@var{endianness}}
> +-fsigned-char  -funsigned-char -fstrict-flex-arrays[=@var{n}] @gol
> +-fsso-struct=@var{endianness}}
>  
>  @item C++ Language Options
>  @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
> @@ -2826,6 +2827,37 @@ The type @code{char} is always a distinct type from each of
>  @code{signed char} or @code{unsigned char}, even though its behavior
>  is always just like one of those two.
>  
> +@item -fstrict-flex-arrays
> +@opindex fstrict-flex-arrays
> +@opindex fno-strict-flex-arrays
> +Treat the trailing array of a structure as a flexible array member in a
> +stricter way.
> +The positive form is equivalent to @option{-fstrict-flex-arrays=3}, which is the
> +strictest.  A trailing array is treated as a flexible array member only when it
> +is declared as a flexible array member per C99 standard onwards.
> +The negative form is equivalent to @option{-fstrict-flex-arrays=0}, which is the
> +least strict.  All trailing arrays of structures are treated as flexible array
> +members.
> +
> +@item -fstrict-flex-arrays=@var{level}
> +@opindex fstrict-flex-arrays=@var{level}
> +Treat the trailing array of a structure as a flexible array member in a
> +stricter way.  The value of @var{level} controls the level of strictness.
> +
> +The possible values of @var{level} are the same as for the
> +@code{strict_flex_array} attribute (@pxref{Variable Attributes}).
> +
> +You can control this behavior for a specific trailing array field of a
> +structure by using the variable attribute @code{strict_flex_array} attribute
> +(@pxref{Variable Attributes}).
> +
> +This option is only valid when flexible array member is supported in the
> +language. FOR ISO C before C99 and ISO C++, no language support for the flexible
> +array member at all, this option will be invalid and a warning will be issued.
> +When -std=gnu89 is specified or C++ with GNU extension, only zero-length array
> +extension and one-size array are supported, as a result, @var{level}=3 will be
> +invalid and a warning will be issued.
> +
>  @item -fsso-struct=@var{endianness}
>  @opindex fsso-struct
>  Set the default scalar storage order of structures and unions to the
> diff --git a/gcc/print-tree.cc b/gcc/print-tree.cc
> index 6d45a4a59669..58a98250cc4f 100644
> --- a/gcc/print-tree.cc
> +++ b/gcc/print-tree.cc
> @@ -517,8 +517,12 @@ print_node (FILE *file, const char *prefix, tree node, int indent,
>  	  fprintf (file, " align:%d warn_if_not_align:%d",
>  		   DECL_ALIGN (node), DECL_WARN_IF_NOT_ALIGN (node));
>  	  if (code == FIELD_DECL)
> -	    fprintf (file, " offset_align " HOST_WIDE_INT_PRINT_UNSIGNED,
> -		     DECL_OFFSET_ALIGN (node));
> +	    {
> +	      fprintf (file, " offset_align " HOST_WIDE_INT_PRINT_UNSIGNED,
> +		       DECL_OFFSET_ALIGN (node));
> +	      fprintf (file, " decl_not_flexarray: %d",
> +		       DECL_NOT_FLEXARRAY (node));
> +	    }
>  
>  	  if (code == FUNCTION_DECL && fndecl_built_in_p (node))
>  	    {
> diff --git a/gcc/testsuite/g++.dg/strict-flex-array-1.C b/gcc/testsuite/g++.dg/strict-flex-array-1.C
> new file mode 100644
> index 000000000000..47adaf7bac4a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/strict-flex-array-1.C
> @@ -0,0 +1,31 @@
> +/* testing the correct usage of attribute strict_flex_array.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +
> +int x __attribute__ ((strict_flex_arrays (1))); /* { dg-error "'strict_flex_arrays' attribute may not be specified for 'x'" } */
> +
> +struct trailing {
> +    int a;
> +    int c __attribute ((strict_flex_arrays)); /* { dg-error "wrong number of arguments specified for 'strict_flex_arrays' attribute" } */
> +};
> +
> +struct trailing_1 {
> +    int a;
> +    int b;
> +    int c __attribute ((strict_flex_arrays (2))); /* { dg-error "'strict_flex_arrays' attribute may not be specified for a non array field" } */
> +};
> +
> +extern int d;
> +
> +struct trailing_array_2 {
> +    int a;
> +    int b;
> +    int c[1] __attribute ((strict_flex_arrays (d))); /* { dg-error "'strict_flex_arrays' attribute argument not an integer" } */
> +};
> +
> +struct trailing_array_3 {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (5))); /* { dg-error "'strict_flex_arrays' attribute argument '5' is not an integer constant between 0 and 3" } */
> +};
> diff --git a/gcc/testsuite/g++.dg/strict-flex-array-2.C b/gcc/testsuite/g++.dg/strict-flex-array-2.C
> new file mode 100644
> index 000000000000..245f8fe0bc73
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/strict-flex-array-2.C
> @@ -0,0 +1,16 @@
> +/* testing the correct usage of flag -fstrict_flex_array for C++.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fstrict-flex-arrays -std=c++98" } */
> +
> +struct trailing_array {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning "attribute ignored since it is not supported with a ISO C\\+\\+" } */
> +};
> +
> +int foo(int a)
> +{
> +  return 0;
> +}
> +
> +/* { dg-warning "is not supported with a ISO C\\+\\+, ignored" ""  { target *-*-* } 0 } */
> diff --git a/gcc/testsuite/g++.dg/strict-flex-array-3.C b/gcc/testsuite/g++.dg/strict-flex-array-3.C
> new file mode 100644
> index 000000000000..2a733a5bccf4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/strict-flex-array-3.C
> @@ -0,0 +1,21 @@
> +/* testing the correct usage of flag -fstrict_flex_array for C++.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fstrict-flex-arrays -std=gnu++98" } */
> +/* { dg-warning "'-fstrict-flex-arrays=3' is not supported for C\\+\\+ with GNU extension, ignored" ""  { target *-*-* } 0 } */
> +
> +struct trailing_array {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning "'strict_flex_arrays' = 3 attribute ignored since it is not supported for C\\+\\+ with GNU extension" } */
> +};
> +
> +struct trailing_array_1 {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (2))); /* { dg-bogus "'strict_flex_arrays' = 3 attribute ignored since it is not supported for C\\+\\+ with GNU extension" } */
> +};
> +
> +int foo(int a)
> +{
> +  return a + 2;
> +}
> diff --git a/gcc/testsuite/g++.dg/strict-flex-array-4.C b/gcc/testsuite/g++.dg/strict-flex-array-4.C
> new file mode 100644
> index 000000000000..804e4cf459ef
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/strict-flex-array-4.C
> @@ -0,0 +1,9 @@
> +/* testing the correct usage of flag -fstrict_flex_array.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fstrict-flex-arrays=2 -std=gnu++98" } */
> +/* { dg-bogus "is not supported for C\\+\\+ with GNU extension, ignored" ""  { target *-*-* } 0 } */
> +
> +int foo(int a)
> +{
> +  return a + 2;
> +}
> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-1.c b/gcc/testsuite/gcc.dg/strict-flex-array-1.c
> new file mode 100644
> index 000000000000..47adaf7bac4a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-1.c
> @@ -0,0 +1,31 @@
> +/* testing the correct usage of attribute strict_flex_array.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +
> +int x __attribute__ ((strict_flex_arrays (1))); /* { dg-error "'strict_flex_arrays' attribute may not be specified for 'x'" } */
> +
> +struct trailing {
> +    int a;
> +    int c __attribute ((strict_flex_arrays)); /* { dg-error "wrong number of arguments specified for 'strict_flex_arrays' attribute" } */
> +};
> +
> +struct trailing_1 {
> +    int a;
> +    int b;
> +    int c __attribute ((strict_flex_arrays (2))); /* { dg-error "'strict_flex_arrays' attribute may not be specified for a non array field" } */
> +};
> +
> +extern int d;
> +
> +struct trailing_array_2 {
> +    int a;
> +    int b;
> +    int c[1] __attribute ((strict_flex_arrays (d))); /* { dg-error "'strict_flex_arrays' attribute argument not an integer" } */
> +};
> +
> +struct trailing_array_3 {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (5))); /* { dg-error "'strict_flex_arrays' attribute argument '5' is not an integer constant between 0 and 3" } */
> +};
> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-2.c b/gcc/testsuite/gcc.dg/strict-flex-array-2.c
> new file mode 100644
> index 000000000000..967a240040dc
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-2.c
> @@ -0,0 +1,15 @@
> +/* testing the correct usage of flag -fstrict_flex_array.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fstrict-flex-arrays -std=c89" } */
> +/* { dg-warning "'-fstrict-flex-arrays' is not supported with a ISO C before C99, ignored" ""  { target *-*-* } 0 } */
> +
> +struct trailing_array {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning "'strict_flex_arrays' attribute ignored since it is not supported with a ISO C before C99" } */
> +};
> +
> +int foo(int a)
> +{
> +  return a + 2;
> +}
> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-3.c b/gcc/testsuite/gcc.dg/strict-flex-array-3.c
> new file mode 100644
> index 000000000000..879de7f203c8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-3.c
> @@ -0,0 +1,21 @@
> +/* testing the correct usage of flag -fstrict_flex_array.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fstrict-flex-arrays -std=gnu89" } */
> +/* { dg-warning "'-fstrict-flex-arrays=3' is not supported with a GNU extension GNU89, ignored" ""  { target *-*-* } 0 } */
> +
> +struct trailing_array {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning "'strict_flex_arrays' = 3 attribute ignored since it is not supported with a GNU extension GNU89" } */
> +};
> +
> +struct trailing_array_1 {
> +    int a;
> +    int b;
> +    int c[0] __attribute ((strict_flex_arrays (2))); /* { dg-bogus "'strict_flex_arrays' = 3 attribute ignored since it is not supported with a GNU extension GNU89" } */
> +};
> +
> +int foo(int a)
> +{
> +  return a + 2;
> +}
> diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-4.c b/gcc/testsuite/gcc.dg/strict-flex-array-4.c
> new file mode 100644
> index 000000000000..ce64c24db301
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/strict-flex-array-4.c
> @@ -0,0 +1,10 @@
> +/* testing the correct usage of flag -fstrict_flex_array.  */   
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fstrict-flex-arrays=2 -std=gnu89" } */
> +/* { dg-bogus "is not supported with a GNU extension GNU89, ignored" ""  { target *-*-* } 0 } */
> +
> +
> +int foo(int a)
> +{
> +  return a + 2;
> +}
> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> index 86a07c282af2..f822cb539dd0 100644
> --- a/gcc/tree-core.h
> +++ b/gcc/tree-core.h
> @@ -1813,7 +1813,10 @@ struct GTY(()) tree_decl_common {
>       TYPE_WARN_IF_NOT_ALIGN.  */
>    unsigned int warn_if_not_align : 6;
>  
> -  /* 14 bits unused.  */
> +  /* In FIELD_DECL, this is DECL_NOT_FLEXARRAY.  */
> +  unsigned int decl_not_flexarray : 1;
> +
> +  /* 13 bits unused.  */
>  
>    /* UID for points-to sets, stable over copying from inlining.  */
>    unsigned int pt_uid;
> diff --git a/gcc/tree-streamer-in.cc b/gcc/tree-streamer-in.cc
> index 196f19c759f2..21e6e8eb1c0a 100644
> --- a/gcc/tree-streamer-in.cc
> +++ b/gcc/tree-streamer-in.cc
> @@ -261,6 +261,7 @@ unpack_ts_decl_common_value_fields (struct bitpack_d *bp, tree expr)
>        else
>  	SET_DECL_FIELD_ABI_IGNORED (expr, val);
>        expr->decl_common.off_align = bp_unpack_value (bp, 8);
> +      DECL_NOT_FLEXARRAY (expr) = (unsigned) bp_unpack_value (bp, 1);
>      }
>  
>    else if (VAR_P (expr))
> diff --git a/gcc/tree-streamer-out.cc b/gcc/tree-streamer-out.cc
> index d39dc158a465..68e40dbdb8f2 100644
> --- a/gcc/tree-streamer-out.cc
> +++ b/gcc/tree-streamer-out.cc
> @@ -229,6 +229,7 @@ pack_ts_decl_common_value_fields (struct bitpack_d *bp, tree expr)
>        else
>  	bp_pack_value (bp, DECL_FIELD_ABI_IGNORED (expr), 1);
>        bp_pack_value (bp, expr->decl_common.off_align, 8);
> +      bp_pack_value (bp, DECL_NOT_FLEXARRAY (expr), 1);
>      }
>  
>    else if (VAR_P (expr))
> diff --git a/gcc/tree.cc b/gcc/tree.cc
> index fed1434d141d..d698e8c9c213 100644
> --- a/gcc/tree.cc
> +++ b/gcc/tree.cc
> @@ -12678,14 +12678,30 @@ array_ref_up_bound (tree exp)
>  }
>  
>  /* Returns true if REF is an array reference, component reference,
> -   or memory reference to an array at the end of a structure.
> -   If this is the case, the array may be allocated larger
> -   than its upper bound implies.  */
> +   or memory reference to an array whose actual size might be larger
> +   than its upper bound implies, there are multiple cases:
> +   A. a ref to a flexible array member at the end of a structure;
> +   B. a ref to an array with a different type against the original decl;
> +      for example:
>  
> +   short a[16] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 };
> +   (*((char(*)[16])&a[0]))[i+8]
> +
> +   C. a ref to an array that was passed as a parameter;
> +      for example:
> +
> +   int test (uint8_t *p, uint32_t t[1][1], int n) {
> +   for (int i = 0; i < 4; i++, p++)
> +     t[i][0] = ...;
> +
> +   FIXME, the name of this routine need to be changed to be more accurate.  */
>  bool
>  array_at_struct_end_p (tree ref)
>  {
> -  tree atype;
> +  /* the TYPE for this array referece.  */
> +  tree atype = NULL_TREE;
> +  /* the FIELD_DECL for the array field in the containing structure.  */
> +  tree afield_decl = NULL_TREE;
>  
>    if (TREE_CODE (ref) == ARRAY_REF
>        || TREE_CODE (ref) == ARRAY_RANGE_REF)
> @@ -12695,7 +12711,10 @@ array_at_struct_end_p (tree ref)
>      }
>    else if (TREE_CODE (ref) == COMPONENT_REF
>  	   && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 1))) == ARRAY_TYPE)
> -    atype = TREE_TYPE (TREE_OPERAND (ref, 1));
> +    {
> +      atype = TREE_TYPE (TREE_OPERAND (ref, 1));
> +      afield_decl = TREE_OPERAND (ref, 1);
> +    }
>    else if (TREE_CODE (ref) == MEM_REF)
>      {
>        tree arg = TREE_OPERAND (ref, 0);
> @@ -12707,6 +12726,7 @@ array_at_struct_end_p (tree ref)
>  	  if (tree fld = last_field (argtype))
>  	    {
>  	      atype = TREE_TYPE (fld);
> +	      afield_decl = fld;
>  	      if (TREE_CODE (atype) != ARRAY_TYPE)
>  		return false;
>  	      if (VAR_P (arg) && DECL_SIZE (fld))
> @@ -12760,13 +12780,16 @@ array_at_struct_end_p (tree ref)
>        ref = TREE_OPERAND (ref, 0);
>      }
>  
> -  /* The array now is at struct end.  Treat flexible arrays as
> +  gcc_assert (!afield_decl
> +	      || (afield_decl && TREE_CODE (afield_decl) == FIELD_DECL));
> +
> +  /* The array now is at struct end.  Treat flexible array member as
>       always subject to extend, even into just padding constrained by
>       an underlying decl.  */
>    if (! TYPE_SIZE (atype)
>        || ! TYPE_DOMAIN (atype)
>        || ! TYPE_MAX_VALUE (TYPE_DOMAIN (atype)))
> -    return true;
> +    return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true;
>  
>    /* If the reference is based on a declared entity, the size of the array
>       is constrained by its given domain.  (Do not trust commons PR/69368).  */
> @@ -12788,9 +12811,9 @@ array_at_struct_end_p (tree ref)
>        if (TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (atype))) != INTEGER_CST
>  	  || TREE_CODE (TYPE_MAX_VALUE (TYPE_DOMAIN (atype))) != INTEGER_CST
>            || TREE_CODE (TYPE_MIN_VALUE (TYPE_DOMAIN (atype))) != INTEGER_CST)
> -	return true;
> +	return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true;
>        if (! get_addr_base_and_unit_offset (ref_to_array, &offset))
> -	return true;
> +	return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true;
>  
>        /* If at least one extra element fits it is a flexarray.  */
>        if (known_le ((wi::to_offset (TYPE_MAX_VALUE (TYPE_DOMAIN (atype)))
> @@ -12798,12 +12821,12 @@ array_at_struct_end_p (tree ref)
>  		     + 2)
>  		    * wi::to_offset (TYPE_SIZE_UNIT (TREE_TYPE (atype))),
>  		    wi::to_offset (DECL_SIZE_UNIT (ref)) - offset))
> -	return true;
> +	return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true;
>  
>        return false;
>      }
>  
> -  return true;
> +  return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true;
>  }
>  
>  /* Return a tree representing the offset, in bytes, of the field referenced
> diff --git a/gcc/tree.h b/gcc/tree.h
> index e6564aaccb7b..f911c0a46e69 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -2993,6 +2993,12 @@ extern void decl_value_expr_insert (tree, tree);
>  #define DECL_PADDING_P(NODE) \
>    (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_3)
>  
> +/* Used in a FIELD_DECL to indicate whether this field is not a flexible
> +   array member. This is only valid for the last array type field of a
> +   structure.  */
> +#define DECL_NOT_FLEXARRAY(NODE) \
> +  (FIELD_DECL_CHECK (NODE)->decl_common.decl_not_flexarray)
> +
>  /* A numeric unique identifier for a LABEL_DECL.  The UID allocation is
>     dense, unique within any one function, and may be used to index arrays.
>     If the value is -1, then no UID has been assigned.  */
> @@ -5531,10 +5537,10 @@ extern tree component_ref_field_offset (tree);
>     returns null.  */
>  enum struct special_array_member
>    {
> -   none,      /* Not a special array member.  */
> -   int_0,     /* Interior array member with size zero.  */
> -   trail_0,   /* Trailing array member with size zero.  */
> -   trail_1    /* Trailing array member with one element.  */
> +    none,	/* Not a special array member.  */
> +    int_0,	/* Interior array member with size zero.  */
> +    trail_0,	/* Trailing array member with size zero.  */
> +    trail_1	/* Trailing array member with one element.  */
>    };
>  
>  /* Return the size of the member referenced by the COMPONENT_REF, using
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)