Re: [GCC13][Patch][V2][1/2]Add a new option -fstrict-flex-array[=n] and attribute strict_flex_array(n) and use it in PR101836

[Qing Zhao <qing.zhao@oracle.com>]

> On Aug 1, 2022, at 3:38 AM, Richard Biener <rguenther@suse.de> wrote:
> 
> On Fri, 29 Jul 2022, Qing Zhao wrote:
> 
>> Hi, Richard,
>> 
>> Thanks a lot for your comments and suggestions. (And sorry for my late reply).
>> 
>>> On Jul 28, 2022, at 3:26 AM, Richard Biener <rguenther@suse.de> wrote:
>>> 
>>> On Tue, 19 Jul 2022, Qing Zhao wrote:
>>> 
>>>> From 3854004802b8e2f132ebf218fc35a632f5e80c6a Mon Sep 17 00:00:00 2001
>>>> From: Qing Zhao <qing.zhao@oracle.com>
>>>> Date: Mon, 18 Jul 2022 17:04:12 +0000
>>>> Subject: [PATCH 1/2] Add a new option -fstrict-flex-array[=n] and new
>>>> attribute strict_flex_array
>>>> 
>>>> 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::).
>>>> 
>>>> '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.
>>>> 
>>>> gcc/c-family/ChangeLog:
>>>> 
>>>> 	* c-attribs.cc (handle_strict_flex_array_attribute): New function.
>>>> 	(c_common_attribute_table): New item for strict_flex_array.
>>>> 	* c.opt (fstrict-flex-array): New option.
>>>> 	(fstrict-flex-array=): New option.
>>>> 
>>>> gcc/c/ChangeLog:
>>>> 
>>>> 	* c-decl.cc (add_flexible_array_elts_to_size): Call new utility
>>>> 	routine flexible_array_member_p.
>>>> 	(is_flexible_array_member_p): New function.
>>>> 	(finish_struct): Set the new DECL_NOT_FLEXARRAY flag.
>>>> 
>>>> gcc/ChangeLog:
>>>> 
>>>> 	* doc/extend.texi: Document strict_flex_array attribute.
>>>> 	* doc/invoke.texi: Document -fstrict-flex-array[=n] option.
>>>> 	* tree-core.h (struct tree_decl_common): New bit field
>>>> 	decl_not_flexarray.
>>>> 	* tree.cc (component_ref_size): Reorg by using new utility functions.
>>>> 	(flexible_array_member_p): New function.
>>>> 	(zero_length_array_p): Likewise.
>>>> 	(one_element_array_p): Likewise.
>>>> 	(flexible_array_type_p): Likewise.
>>>> 	* tree.h (DECL_NOT_FLEXARRAY): New flag.
>>>> 	(zero_length_array_p): New function prototype.
>>>> 	(one_element_array_p): Likewise.
>>>> 	(flexible_array_member_p): Likewise.
>>>> 
>>>> gcc/testsuite/ChangeLog:
>>>> 
>>>> 	* gcc.dg/strict-flex-array-1.c: New test.
>>>> ---
>>>> gcc/c-family/c-attribs.cc                  |  47 ++++++++
>>>> gcc/c-family/c.opt                         |   7 ++
>>>> gcc/c/c-decl.cc                            |  91 +++++++++++++--
>>>> gcc/doc/extend.texi                        |  25 ++++
>>>> gcc/doc/invoke.texi                        |  27 ++++-
>>>> gcc/testsuite/gcc.dg/strict-flex-array-1.c |  31 +++++
>>>> gcc/tree-core.h                            |   5 +-
>>>> gcc/tree.cc                                | 130 ++++++++++++++-------
>>>> gcc/tree.h                                 |  16 ++-
>>>> 9 files changed, 322 insertions(+), 57 deletions(-)
>>>> create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-1.c
>>>> 
>>>> diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
>>>> index c8d96723f4c..10d16532f0d 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_array_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 *);
>>>> @@ -367,6 +369,8 @@ 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_array",      1, 1, false, false, false, false,
>>>> +			      handle_strict_flex_array_attribute, NULL },
>>>> { "weak",                   0, 0, true,  false, false, false,
>>>> 			      handle_weak_attribute, NULL },
>>>> { "noplt",                   0, 0, true,  false, false, false,
>>>> @@ -2498,6 +2502,49 @@ handle_warn_if_not_aligned_attribute (tree *node, tree name,
>>>> 					  no_add_attrs, true);
>>>> }
>>>> 
>>>> +/* Handle a "strict_flex_array" attribute; arguments as in
>>>> +   struct attribute_spec.handler.  */
>>>> +
>>>> +static tree
>>>> +handle_strict_flex_array_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;
>>>> +    }
>>>> +
>>>> +  return NULL_TREE;
>>>> +}
>>>> +
>>>> /* Handle a "weak" attribute; arguments as in
>>>>  struct attribute_spec.handler.  */
>>>> 
>>>> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
>>>> index 44e1a60ce24..864cd8df1d3 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-array
>>>> +C C++ Common Alias(fstrict-flex-array=,3,0)
>>>> +
>>>> +fstrict-flex-array=
>>>> +C C++ Common Joined RejectNegative UInteger Var(flag_strict_flex_array) Init(0) IntegerRange(0,3)
>>>> +-fstrict-flex-array=<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 ae8990c138f..14defae9584 100644
>>>> --- a/gcc/c/c-decl.cc
>>>> +++ b/gcc/c/c-decl.cc
>>>> @@ -5013,10 +5013,7 @@ 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_p (type))
>>>>   {
>>>>     complete_array_type (&type, elt, false);
>>>>     DECL_SIZE (decl)
>>>> @@ -8720,6 +8717,80 @@ 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_array;
>>>> +  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_p (TREE_TYPE (x));
>>>> +  bool is_one_element_array = one_element_array_p (TREE_TYPE (x));
>>>> +  bool is_flexible_array = flexible_array_member_p (TREE_TYPE (x));
>>>> +
>>>> +  unsigned int strict_flex_array_level = flag_strict_flex_array;
>>>> +
>>>> +  tree attr_strict_flex_array = lookup_attribute ("strict_flex_array",
>>>> +						  DECL_ATTRIBUTES (x));
>>>> +  /* if there is a strict_flex_array attribute attached to the field,
>>>> +     override the flag_strict_flex_array.  */
>>>> +  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 +8852,8 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
>>>> bool saw_named_field = false;
>>>> for (x = fieldlist; x; x = DECL_CHAIN (x))
>>>>   {
>>>> +      bool is_last_field = (DECL_CHAIN (x) == NULL_TREE);
>>>> +
>>>>     if (TREE_TYPE (x) == error_mark_node)
>>>> 	continue;
>>>> 
>>>> @@ -8819,10 +8892,7 @@ 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_p (TREE_TYPE (x)))
>>>> 	{
>>>> 	  if (TREE_CODE (t) == UNION_TYPE)
>>>> 	    {
>>>> @@ -8830,7 +8900,7 @@ 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 +8920,9 @@ 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/doc/extend.texi b/gcc/doc/extend.texi
>>>> index dfbe33ac652..7451410a011 100644
>>>> --- a/gcc/doc/extend.texi
>>>> +++ b/gcc/doc/extend.texi
>>>> @@ -7436,6 +7436,31 @@ 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_array} variable attribute
>>>> +@item strict_flex_array (@var{level})
>>>> +The @code{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. @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.
>>> 
>>> How is level 3 (thus -fstrict-flex-array) interpreted when you specify 
>>> -std=c89?  How for -std=gnu89?
>> 
>> 1. what’s the major difference between -std=c89 and -std=gnu89 on flexible array? (Checked online, cannot find a concrete answer on this).
>> 	** my understanding is:   -std=c89 will not support any flexible array (neither [], [0], [1]), but -std=gnu89 will support [0] and [1], but not [].
>>         Is this correct?
> 
> Yes.
> 
>> If my answer to the first question is correct, then:
>> 
>> 2. When -fstrict-flex-array=n and -std=c89 present at the same time, which one has the higher priority? 
>>     	** I think that -std=c89 should be honored over -fstrict-flex-array, therefore we should disable -fstrict-flex-array=n when n > 0  and issue warnings to the user.
>> 
>> 
>> 3. how about -fstrict-flex-array=n and -std=gnu89 present at the same time? 
>>     	** When -std=gnu89 present, [] is not supported. So, we need to issue an warning to disable -fstrict-flex-array=3; but level 1 and level 2 is Okay.
>> 
>> We also need to document the above.
>> 
>> Let me know if you have any more comment and suggestions here.
> 
> In my opinion -fstrict-flex-array only makes sense with C99 and above.  
> The extra sub-levels allowing [0] or [1] are of questionable benefit.
The multiple-levels control for -fstrict-flex-arrays was an agreement on the discussion of PR101836:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836

Please see comment#17 till #25 for the details.

A summary of the discussion is:  (Please comment on the following paragraph if you see any issue with it)

=====
Flexible Array Member (FAM) is a feature introduced in the C99 standard of the C language in May 2000.  It's used as the last element of a structure which is really a header for a variable-length object.
This feature was officially standardized in C99. However, compilers (GCC, Micorsoft compiler, etc.) supported this feature well before C99, with the following variants:
  A. trailing zero-length array of a structure was treated as FAM.  
     Before C99, a valid GCC extension, zero-length array was used to support flexible array member.  See more details at:  https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html.
  B. trailing one-element array of a structure was treated as FAM.
     In the absence of the zero-length array extension, in ISO C90, one-element arrays at the end of structures were used to represent FAMs as a convertion.
  C. any trailing array of a structure was treated as FAM.
     Even earlier time, in the absence of both zero-length array GCC extension and one-element array convention, all trailing arrays of structures could be used as a FAM.     
As a result, older codes (before C99) might include any of the above variants (A, B, and C) to represent FAMs. 
Another complication is C++, standard C++ doesn't allow either C99 flexible array members or zero-length array. A C++ programmer has to use the GCC zero-length array extension or one-element array convention for the purpose of FAM.
=====

As mentioned by Jakub in comment #25: 

"differentiating between only allowing [] as flex, or [] and [0],
or [], [0] and [1], or any trailing array is useful."

> 
> I think that with -fstrict-flex-array we're missing a -Wstrict-flex-array
> that would diagnose accesses that are no longer treated as flex array
> access but would be without -fstrict-flex-array?  The goal of
> -fstrict-flex-array + -Wstrict-flex-array is to make code standard
> conformant, no?  Not to enable extra optimization for [1] arrays when
> we know [0] is used as flexarray?

Yes, I agree, and this will make the feature more complete and more
 useful to help users to get rid of the non-standard-comforming styles. 

Please see comments #23, #35

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836#c23
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836#c35

A summary is:

====
I think that -Wstrict-flex-arrays will need to be cooperated with -fstrict-flex-arrays=N, i.e, only when -fstrict-flex-arrays=N is presenting, -Wstrict-flex-arrays will be valid and report the warnings when see a [0], or [1], or any trailing array based on N:

when -fstrict-flex-arrays
=0, -Wstrict-flex-arrays will NOT issue any warnings;
=1, -Wstrict-flex-arrays will issue warnings when an array ref's index is larger than the upper bounds of a trailing array that is a regular trailing array;
=2, -Wstrict-flex-arrays will issue warnings when an array ref's index is larger than the upper bounds of a trailing array that is a regular trailing array or [1];
=3, -Wstrict-flex-arrays will issue warnings when an array ref's index is larger than the upper bounds of a trailing array that is a regular trailing array or [1], or [0].

let me know if you have any comment and suggestion on this.

====


> 
>>> 
>>>> +
>>>> +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]".
>>> 
>>> Given the above does adding level 2 make sense given that [0] is a GNU
>>> extension?
>> I think Kees already answered this question.
>>> 
>>>> +This attribute can be used with or without @option{-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.
>>>> +
>>>> +
>>>> @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 94fe57aa4e2..9befe601817 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-array[=@var{n}] @gol
>>>> +-fsso-struct=@var{endianness}}
>>>> 
>>>> @item C++ Language Options
>>>> @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
>>>> @@ -2825,6 +2826,30 @@ 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-array
>>>> +@opindex fstrict-flex-array
>>>> +@opindex fno-strict-flex-array
>>>> +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-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 @option{-fstrict-flex-array=0}, which is the
>>>> +least strict.  All trailing arrays of structures are treated as flexible array
>>>> +members.
>>>> +
>>>> +@item -fstrict-flex-array=@var{level}
>>>> +@opindex fstrict-flex-array=@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}).
>>>> +
>>>> @item -fsso-struct=@var{endianness}
>>>> @opindex fsso-struct
>>>> Set the default scalar storage order of structures and unions to the
>>>> 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 00000000000..ec886c99b25
>>>> --- /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_array (1))); /* { dg-error "'strict_flex_array' attribute may not be specified for 'x'" } */
>>>> +
>>>> +struct trailing {
>>>> +    int a;
>>>> +    int c __attribute ((strict_flex_array)); /* { dg-error "wrong number of arguments specified for 'strict_flex_array' attribute" } */
>>>> +};
>>>> +
>>>> +struct trailing_1 {
>>>> +    int a;
>>>> +    int b;
>>>> +    int c __attribute ((strict_flex_array (2))); /* { dg-error "'strict_flex_array' 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_array (d))); /* { dg-error "'strict_flex_array' attribute argument not an integer" } */
>>>> +};
>>>> +
>>>> +struct trailing_array_3 {
>>>> +    int a;
>>>> +    int b;
>>>> +    int c[0] __attribute ((strict_flex_array (5))); /* { dg-error "'strict_flex_array' attribute argument '5' is not an integer constant between 0 and 3" } */
>>>> +};
>>>> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
>>>> index ea9f281f1cc..458c6e6ceea 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.  */
>>> 
>>> I've not seen it so you are probably missing it - the bit has to be
>>> streamed in tree-streamer-{in,out}.cc to be usable from LTO.
>> 
>> You mean add it to the routine “unpack_ts_decl_common_value_fields” of tree-streamer-in.cc
>> And “pack_ts_decl_common_value_fields” of tree-streamer-out.cc?
> 
> Yes.
> 
>> 
>>> C++ module streaming also needs to handle it.
>> 
>> Which file is for this C++ module streaming?
> 
> Not sure, maybe cp/module.cc

Just checked this file, looks like it’s “Experimental”:
/* C++ modules.  Experimental!

Is it used right now? To whom I can consult with to get more detail on C++?

> 
>>> 
>>>> 
>>>> /* UID for points-to sets, stable over copying from inlining.  */
>>>> unsigned int pt_uid;
>>>> diff --git a/gcc/tree.cc b/gcc/tree.cc
>>>> index 84000dd8b69..02e274699fb 100644
>>>> --- a/gcc/tree.cc
>>>> +++ b/gcc/tree.cc
>>>> @@ -12862,7 +12862,7 @@ get_initializer_for (tree init, tree decl)
>>>> /* Determines the size of the member referenced by the COMPONENT_REF
>>>>  REF, using its initializer expression if necessary in order to
>>>>  determine the size of an initialized flexible array member.
>>>> -   If non-null, set *ARK when REF refers to an interior zero-length
>>>> +   If non-null, set *SAM when REF refers to an interior zero-length
>>>>  array or a trailing one-element array.
>>>>  Returns the size as sizetype (which might be zero for an object
>>>>  with an uninitialized flexible array member) or null if the size
>>>> @@ -12878,16 +12878,32 @@ component_ref_size (tree ref, special_array_member *sam /* = NULL */)
>>>>   sam = &sambuf;
>>>> *sam = special_array_member::none;
>>>> 
>>>> +  /* Whether this ref is an array at the end of a structure.  */
>>>> +  bool trailing = array_at_struct_end_p (ref);
>>>> +
>>> 
>>> actually array_at_struct_end_p returns whether ref possibly refers to
>>> a trailing array.  In particular it may return false for arrays at
>>> struct end with a known length as in a.b[i] for the reference to global 
>>> 'a':
>>> 
>>> struct { int b[1]; } a;
>> 
>> Yes, I noticed this behavior during my recent debugging of this routine. I thought it’s a bug and planned to file another bug against it.
>> Looks like that this is an expected behavior.
>> 
>> Then I really feel the name and the comments of the routine is very confusing…
>> Shall we change the name of this routine to a more descriptive one? For example, “flexible_array_member_p”? 
> 
> Note the routine is about classifying a concrete reference, so a better
> name could be flex_array_ref_p ().  The name change should be done
> separately (if at all).

Okay. 

> 
>>> 
>>> so in the end it should be array_at_struct_end_p also honoring
>>> DECL_NOT_FLEXARRAY.
>> 
>> Then it’s make more sense to check DECL_NOT_FLEXARRAY inside this utility routine?
> 
> Yes.
> 
>>> 
>>>> /* The object/argument referenced by the COMPONENT_REF and its type.  */
>>>> tree arg = TREE_OPERAND (ref, 0);
>>>> tree argtype = TREE_TYPE (arg);
>>>> -  /* The referenced member.  */
>>>> -  tree member = TREE_OPERAND (ref, 1);
>>>> 
>>>> +  /* The referenced field member.  */
>>>> +  tree member = TREE_OPERAND (ref, 1);
>>>> +  tree memtype = TREE_TYPE (member);
>>>> tree memsize = DECL_SIZE_UNIT (member);
>>>> +
>>>> +  bool is_zero_length_array_ref = zero_length_array_p (memtype);
>>>> +  bool is_constant_length_array_ref = false;
>>>> +  bool is_one_element_array_ref
>>>> +	= one_element_array_p (memtype, &is_constant_length_array_ref);
>>>> +
>>>> +  /* Determine the type of the special array member.  */
>>>> +  if (is_zero_length_array_ref)
>>>> +    *sam = trailing ? special_array_member::trail_0
>>>> +	   : special_array_member::int_0;
>>>> +  else if (is_one_element_array_ref && trailing)
>>>> +    *sam = special_array_member::trail_1;
>>>> +
>>>> if (memsize)
>>>>   {
>>>> -      tree memtype = TREE_TYPE (member);
>>>>     if (TREE_CODE (memtype) != ARRAY_TYPE)
>>>> 	/* DECL_SIZE may be less than TYPE_SIZE in C++ when referring
>>>> 	   to the type of a class with a virtual base which doesn't
>>>> @@ -12897,50 +12913,30 @@ component_ref_size (tree ref, special_array_member *sam /* = NULL */)
>>>> 	return (tree_int_cst_equal (memsize, TYPE_SIZE_UNIT (memtype))
>>>> 		? memsize : NULL_TREE);
>>>> 
>>>> -      bool trailing = array_at_struct_end_p (ref);
>>>> -      bool zero_length = integer_zerop (memsize);
>>>> -      if (!trailing && !zero_length)
>>>> +      if (!trailing && !is_zero_length_array_ref)
>>>> 	/* MEMBER is either an interior array or is an array with
>>>> 	   more than one element.  */
>>>> 	return memsize;
>>>> 
>>>> -      if (zero_length)
>>>> -	{
>>>> -	  if (trailing)
>>>> -	    *sam = special_array_member::trail_0;
>>>> -	  else
>>>> -	    {
>>>> -	      *sam = special_array_member::int_0;
>>>> -	      memsize = NULL_TREE;
>>>> -	    }
>>>> -	}
>>>> +      if (*sam != special_array_member::trail_1
>>>> +	  && is_constant_length_array_ref)
>>>> +	/* MEMBER is a constant length array which is not a one-element
>>>> +	   trailing array.  */
>>>> +	return memsize;
>>>> 
>>>> -      if (!zero_length)
>>>> -	if (tree dom = TYPE_DOMAIN (memtype))
>>>> -	  if (tree min = TYPE_MIN_VALUE (dom))
>>>> -	    if (tree max = TYPE_MAX_VALUE (dom))
>>>> -	      if (TREE_CODE (min) == INTEGER_CST
>>>> -		  && TREE_CODE (max) == INTEGER_CST)
>>>> -		{
>>>> -		  offset_int minidx = wi::to_offset (min);
>>>> -		  offset_int maxidx = wi::to_offset (max);
>>>> -		  offset_int neltsm1 = maxidx - minidx;
>>>> -		  if (neltsm1 > 0)
>>>> -		    /* MEMBER is an array with more than one element.  */
>>>> -		    return memsize;
>>>> -
>>>> -		  if (neltsm1 == 0)
>>>> -		    *sam = special_array_member::trail_1;
>>>> -		}
>>>> +      if (*sam == special_array_member::int_0)
>>>> +	memsize = NULL_TREE;
>>>> 
>>>> -      /* For a reference to a zero- or one-element array member of a union
>>>> -	 use the size of the union instead of the size of the member.  */
>>>> +      /* For a reference to a flexible array member, an interior zero length
>>>> +	 array, or an array with variable length of a union, use the size of
>>>> +	 the union instead of the size of the member.  */
>>>>     if (TREE_CODE (argtype) == UNION_TYPE)
>>>> 	memsize = TYPE_SIZE_UNIT (argtype);
>>>>   }
>>>> 
>>>> -  /* MEMBER is either a bona fide flexible array member, or a zero-length
>>>> -     array member, or an array of length one treated as such.  */
>>>> +  /* MEMBER now is a flexible array member, an interior zero length array, or
>>>> +     an array with variable length.  We need to decide its size from its
>>>> +     initializer.  */
>>>> 
>>>> /* If the reference is to a declared object and the member a true
>>>>    flexible array, try to determine its size from its initializer.  */
>>>> @@ -14351,6 +14347,59 @@ default_is_empty_record (const_tree type)
>>>> return is_empty_type (TYPE_MAIN_VARIANT (type));
>>>> }
>>>> 
>>>> +/* Determine whether TYPE is a ISO flexible array memeber type "[]".  */
>>> 
>>> ISO C99
>> 
>> Okay, will add this.
>>> 
>>>> +bool
>>>> +flexible_array_member_p (const_tree type)
>>> 
>>> since you pass in a type a better name would be
>>> flexible_array_type_p?
>> Okay, how about “flexible_array_member_type_p”? (Since “flexible array member” is a complete concept).
> 
> works for me
> 
>>> 
>>>> +{
>>>> +  if (TREE_CODE (type) == ARRAY_TYPE
>>>> +      && TYPE_SIZE (type) == NULL_TREE
>>>> +      && TYPE_DOMAIN (type) != NULL_TREE
>>> 
>>> why require a specified TYPE_DOMAIN?
>> 
>> There are multiple places in the current GCC used the following sequence:
>> 
>> -      if (TREE_CODE (type)) == ARRAY_TYPE
>> -         && TYPE_SIZE (type) == NULL_TREE
>> -         && TYPE_DOMAIN (type) != NULL_TREE
>> -         && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
>> 
>> To check whether the type is a flexible_array_member type.  
>> (For example, the routine “add_flexible_array_elts_to_size” in c/c-decl.cc
>> 			the routine “finish_struct” in c/c-decl.cc
>> 			the routine “flexible_array_type_p” in tree.cc)
>> 
>> That’s the reason I come up with this common routine to replace all these sequences.
>> 
>> 
>>>> +      && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE)
>>> 
>>> and why a NULL TYPE_MAX_VALUE?  Isn't an unknown TYPE_SIZE enough?
>> 
>> Does the current FE generate such IR for a []?  An array type, without TYPE_SIZE, with a TYPE_DOMAIN, but the MAX_VALUE of the TYPE_DOMAIN is NULL?
>> 
>>> 
>>> That said, I'm not sure providing this abstraction is a good idea
>>> given the use I see is in frontend code.
>> 
>> This one is also used in middle-end, for example “flexible_array_type_p” in tree.cc.
> 
> That was originally in c-decl.c, seems some target wanted to use it.  The
> issue with this is that it tests the C frontend way of declaring a flex
> array (and it is used by the frontend), but there are many other possible
> representations the middle-end should classify as flex array.
> 
> The Objective C frontend also has a function named this way and it seems
> to be a 1:1 copy :/
> 
> The nios2 use of the function doesn't make much sense to me - externals
> should not end up in _any_ section!?

What’s you mean by “nios2” ?  Not quite understand this sentence. -:) could you explain a little bit?

> 
> So I'd rather move this function back to where it came from, ideally
> to c-family/, removing the copy in objective C ...

Okay, I will try  this in the next version.
> 
>>> 
>>>> +    return true;
>>>> +
>>>> +  return false;
>>>> +}
>>>> +
>>>> +/* Determine whether TYPE is a zero-length array type "[0]".  */
>>>> +bool
>>>> +zero_length_array_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)
>>> 
>>> that again seems very C(?) frontend specific, please drop it.
>> Currently, the middle-end utility routine “component_ref_size” need to check zero_length_array, one_element_array, etc, 
>> So, this is not only a FE specific routine.
> 
> Sigh, it's nother strange function that was introduced just for 
> diagnostics (so it's not "correct"), it shouldn't have ended up in
> tree.cc IMHO.

The codes in GCC to handle flexible array are really messy, I hope that we can make it clean and consistent through this work. 
Of course gradually…

> 
>> And I think that for making the -fstrict-flex-array work clear, we might want to emphasize  and distinguish the concepts of 
>> 
>> []          flexible_array_member_type_p
>> [0]        zero_length_array_type_p
>> [1]        one_element_array_type_p
>> 
>> Across GCC.
> 
> Why?

Because the whole confusion of flexible array handlings in our compiler started from the confusion of these concepts.
During my study of this whole problem, I found that these concepts were really confusion, and after I was finally clear on
These concepts, I started to know how to resolve the whole issue. 

In our GCC doc, https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

We already have such concepts, but not very clear.  
I think making these concepts clear is very important to resolve such messy situation in GCC.

>  The only important thing to the middle-end is whether the
> size of the array is known (aka array_at_struct_end_p).  This
> routine classifies it with

But whether the size of the array is known depends on whether the array is a

[0],
[1],
[]

+  -fstrict-flex-arrays=n


> 
>  /* The array now is at struct end.  Treat flexible arrays 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;

This sequence is only for identifying []. Right?

The [0] and [1] is not handled by the above.

> 
> any flexible_array_member_type_p that covers a different subset of
> flex-array types would be hugely confusing.

Don’t quite understand this sentence...
> 
>> 
>>> 
>>>> +	return true;
>>>> +  return false;
>>>> +}
>>>> +
>>>> +/* Determine whether TYPE is a one-element array type "[1]".
>>>> +   Set IS_CONSTANT_LENGTH to true if the length is constant,
>>>> +   otherwise, IS_CONSTANT_LENGTH is set to false.  */
>>>> +bool
>>>> +one_element_array_p (const_tree type, bool *is_constant_length /* = NULL */)
>>>> +{
>>>> +  if (is_constant_length)
>>>> +    *is_constant_length = false;
>>>> +
>>>> +  if (TREE_CODE (type) == ARRAY_TYPE)
>>>> +    if (tree dom = TYPE_DOMAIN (type))
>>>> +      if (tree min = TYPE_MIN_VALUE (dom))
>>>> +	if (tree max = TYPE_MAX_VALUE (dom))
>>>> +	  if (TREE_CODE (min) == INTEGER_CST
>>>> +	      && TREE_CODE (max) == INTEGER_CST)
>>>> +	    {
>>>> +	      offset_int minidx = wi::to_offset (min);
>>>> +	      offset_int maxidx = wi::to_offset (max);
>>>> +	      offset_int neltsm1 = maxidx - minidx;
>>>> +	      if (is_constant_length)
>>>> +		*is_constant_length = true;
>>>> +	      if (neltsm1 == 0)
>>>> +		return true;
>>>> +	    }
>>> 
>>> I'd say likewise.  Maybe move them to c-family/c-common.{cc,h} instead
>>> in a more specialized way for the single use you have?
>> 
>> It’s not single use, it’s also used in “component_ref_size” routine. 
> 
> Don't copy from a routine that's not designed to be "correct”.

Okay….


>  In
> fact the middle-end already has array_type_nelts, so one_element_array_p
> can be written as integer_zerop (array_type_nelts (type)).  It also
> has the comment
> 
>  /* TYPE_MAX_VALUE may not be set if the array has unknown length.  */
>  if (!max)
>    {
>      /* zero sized arrays are represented from C FE as complete types 
> with
>         NULL TYPE_MAX_VALUE and zero TYPE_SIZE, while C++ FE represents
>         them as min 0, max -1.  */
>      if (COMPLETE_TYPE_P (type)
>          && integer_zerop (TYPE_SIZE (type))
>          && integer_zerop (min))
>        return build_int_cst (TREE_TYPE (min), -1);

Thanks for the info, I will check on the above, and rewrite “one_element_array_p” with “array_type_nelts”.

Qing
> 
> Richard.
> 
>> Thanks a lot for your comments.
>> 
>> Qing
>>> 
>>>> +  return false;
>>>> +}
>>>> +
>>>> /* Determine whether TYPE is a structure with a flexible array member,
>>>>  or a union containing such a structure (possibly recursively).  */
>>>> 
>>>> @@ -14367,10 +14416,7 @@ flexible_array_type_p (const_tree type)
>>>> 	  last = x;
>>>>     if (last == NULL_TREE)
>>>> 	return false;
>>>> -      if (TREE_CODE (TREE_TYPE (last)) == ARRAY_TYPE
>>>> -	  && TYPE_SIZE (TREE_TYPE (last)) == NULL_TREE
>>>> -	  && TYPE_DOMAIN (TREE_TYPE (last)) != NULL_TREE
>>>> -	  && TYPE_MAX_VALUE (TYPE_DOMAIN (TREE_TYPE (last))) == NULL_TREE)
>>>> +      if (flexible_array_member_p (TREE_TYPE (last)))
>>>> 	return true;
>>>>     return false;
>>>>   case UNION_TYPE:
>>>> diff --git a/gcc/tree.h b/gcc/tree.h
>>>> index e6564aaccb7..3107de5b499 100644
>>>> --- a/gcc/tree.h
>>>> +++ b/gcc/tree.h
>>>> @@ -2993,6 +2993,11 @@ 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.  */
>>>> +#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 +5536,10 @@ 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
>>>> @@ -6489,6 +6494,9 @@ extern void gt_pch_nx (tree &, gt_pointer_operator, void *);
>>>> extern bool nonnull_arg_p (const_tree);
>>>> extern bool is_empty_type (const_tree);
>>>> extern bool default_is_empty_record (const_tree);
>>>> +extern bool zero_length_array_p (const_tree);
>>>> +extern bool one_element_array_p (const_tree, bool * = NULL);
>>>> +extern bool flexible_array_member_p (const_tree);
>>>> extern bool flexible_array_type_p (const_tree);
>>>> extern HOST_WIDE_INT arg_int_size_in_bytes (const_tree);
>>>> extern tree arg_size_in_bytes (const_tree);
>>>> 
>>> 
>>> -- 
>>> 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)
>> 
>> 
> 
> -- 
> 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)