[v8] attribs: Implement -Wno-attributes=vendor::attr [PR101940]

  On Tue, Nov 09, 2021 at 02:17:14PM -0500, Marek Polacek wrote:
> On Tue, Nov 09, 2021 at 12:27:28PM -0500, Jason Merrill wrote:
> > On 11/9/21 10:55, Marek Polacek wrote:
> > > On Tue, Nov 09, 2021 at 08:09:10AM +0100, Bernhard Reutner-Fischer wrote:
> > > > On Tue, 9 Nov 2021 00:12:10 -0500
> > > > Jason Merrill <jason@redhat.com> wrote:
> > > > 
> > > > > On 11/8/21 20:41, Marek Polacek wrote:
> > > > > > On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:
> > > > 
> > > > > > +  for (auto opt : v)
> > > > > > +    {
> > > > > > +      char *cln = strstr (opt, "::");
> > > > > > +      /* We don't accept '::attr'.  */
> > > > > > +      if (cln == nullptr || cln == opt)
> > > > > > +	{
> > > > > > +	  error ("wrong argument to ignored attributes");
> > > > > > +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> > > > > > +	  continue;
> > > > > > +	}
> > > > > > +      char *vendor_start = opt;
> > > > > > +      ptrdiff_t vendor_len = cln - opt;
> > > > > > +      char *attr_start = cln + 2;
> > > > > > +      /* This could really use rawmemchr :(.  */
> > > > > > +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
> > > > > > +      /* Verify that they look valid.  */
> > > > > > +      auto valid_p = [](const char *const s, ptrdiff_t len) {
> > > > > > +	for (int i = 0; i < len; ++i)
> > > > > > +	  if (!ISALNUM (*s) && *s != '_')
> > > > > > +	    return false;
> > > > > > +	return true;
> > > > > > +      };
> > > > > > +      if (!valid_p (vendor_start, vendor_len)
> > > > > > +	  || !valid_p (attr_start, attr_len))
> > > > > > +	{
> > > > > > +	  error ("wrong argument to ignored attributes");
> > > > > > +	  continue;
> > > > > > +	}
> > > > > > +      /* Turn "__attr__" into "attr" so that we have a canonical form of
> > > > > > +	 attribute names.  Likewise for vendor.  */
> > > > > > +      auto strip = [](char *&s, ptrdiff_t &l) {
> > > > > > +	if (l > 4 && s[0] == '_' && s[1] == '_'
> > > > > > +	    && s[l - 1] == '_' && s[l - 2] == '_')
> > > > > > +	  {
> > > > > > +	    s += 2;
> > > > > > +	    l -= 4;
> > > > > > +	  }
> > > > > > +      };
> > > > > > +      strip (attr_start, attr_len);
> > > > > > +      strip (vendor_start, vendor_len);
> > > > > > +      /* We perform all this hijinks so that we don't have to copy OPT.  */
> > > > > > +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
> > > > > > +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
> > > > > > +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
> > > > > > +	 register it twice would lead to a crash.  */
> > > > > > +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
> > > > > > +	continue;
> > > > > 
> > > > > Hmm, this looks like it isn't handling the case of previously ignoring
> > > > > vendor::; it seems we'll look for vendor::<empty string> instead, not
> > > > > find it, and register again.
> > 
> > > Yes, for -Wno-attributes=vendor::,vendor:: we call register_scoped_attributes
> > > twice, but I think that's OK: register_scoped_attributes will see that
> > > find_attribute_namespace finds the namespace and returns without
> > > creating a new  one.
> > > 
> > > I think the current code handles -Wno-attributes=vendor::a,vendor:: well so
> > > I'm not sure if I should change it.
> > 
> > Makes sense.  But we should be able to avoid calling
> > lookup_scoped_attribute_spec, and even get_identifier_with_length (attr...),
> > if attr_len is 0.
>  
> Duh, of course.  Also no need to canonicalize an empty string.
> 
> > > > I don't know if there are __attrib with 2 leading underscores but no
> > > > trailing that we accept and should normalize?
> > > > 
> > > > And it is surprising that we do not have a simple normalize_attr_name().
> > > > There must be existing spots where we would normalize attribute names?
> > > > extract_attribute_substring does about the same but with a struct substring(?).
> > > > Maybe that's just to avoid a normal string hash.
> > > 
> > > We have canonicalize_attr_name which I based my code on.
> > 
> > We could factor out of that function an overload equivalent to your strip
> > lambda?
> 
> OK.  Since it's taking a reference and I wanted it to work both with a size_t
> and ptrdiff_t, I made it a template.  Is is too much?

OK, this time for real.  Here's another version, which doesn't crash on
-Wno-attributes=c::____.  I apologize for the number of takes.  :-(

Bootstrap/regtest running on ppc64le-linux-gnu.  OK if it passes?

-- >8 --
It is desirable for -Wattributes to warn about e.g.

[[deprecate]] void g(); // typo, should warn

However, -Wattributes also warns about vendor-specific attributes
(that's because lookup_scoped_attribute_spec -> find_attribute_namespace
finds nothing), which, with -Werror, causes grief.  We don't want the
-Wattributes warning for

[[company::attr]] void f();

GCC warns because it doesn't know the "company" namespace; it only knows
the "gnu" and "omp" namespaces.  We could entirely disable warning about
attributes in unknown scopes but then the compiler would also miss typos
like

  [[company::attrx]] void f();

or

  [[gmu::warn_used_result]] int write();

so that is not a viable solution.  A workaround is to use a #pragma:

  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wattributes"
  [[company::attr]] void f() {}
  #pragma GCC diagnostic pop

but that's a mouthful and awkward to use and could also hide typos.  In
fact, any macro-based solution doesn't seem like a way forward.

This patch implements -Wno-attributes=, which takes these arguments:

company::attr
company::

This option should go well with using @file: the user could have a file
containing
-Wno-attributes=vendor::attr1,vendor::attr2
and then invoke gcc with '@attrs' or similar.

I've also added a new pragma which has the same effect:

The pragma along with the new option should help with various static
analysis tools.

	PR c++/101940

gcc/ChangeLog:

	* attribs.c (struct scoped_attributes): Add a bool member.
	(lookup_scoped_attribute_spec): Forward declare.
	(register_scoped_attributes): New bool parameter, defaulted to
	false.  Use it.
	(handle_ignored_attributes_option): New function.
	(free_attr_data): New function.
	(init_attributes): Call handle_ignored_attributes_option.
	(attr_namespace_ignored_p): New function.
	(decl_attributes): Check attr_namespace_ignored_p before
	warning.
	* attribs.h (free_attr_data): Declare.
	(register_scoped_attributes): Adjust declaration.
	(handle_ignored_attributes_option): Declare.
	(canonicalize_attr_name): New function template.
	(canonicalize_attr_name): Use it.
	* common.opt (Wattributes=): New option with a variable.
	* doc/extend.texi: Document #pragma GCC diagnostic ignored_attributes.
	* doc/invoke.texi: Document -Wno-attributes=.
	* opts.c (common_handle_option) <case OPT_Wattributes_>: Handle.
	* plugin.h (register_scoped_attributes): Adjust declaration.
	* toplev.c (compile_file): Call free_attr_data.

gcc/c-family/ChangeLog:

	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
	ignored_attributes.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-1.c: New test.
	* c-c++-common/Wno-attributes-2.c: New test.
	* c-c++-common/Wno-attributes-3.c: New test.
---
 gcc/attribs.c                                 | 127 +++++++++++++++++-
 gcc/attribs.h                                 |  28 +++-
 gcc/c-family/c-pragma.c                       |  37 ++++-
 gcc/common.opt                                |   9 +-
 gcc/doc/extend.texi                           |  19 +++
 gcc/doc/invoke.texi                           |  20 +++
 gcc/opts.c                                    |  20 +++
 gcc/plugin.h                                  |   4 +-
 gcc/testsuite/c-c++-common/Wno-attributes-1.c |  55 ++++++++
 gcc/testsuite/c-c++-common/Wno-attributes-2.c |  56 ++++++++
 gcc/testsuite/c-c++-common/Wno-attributes-3.c |   9 ++
 gcc/toplev.c                                  |   2 +
 12 files changed, 374 insertions(+), 12 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-1.c
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-2.c
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-3.c


base-commit: 8875a92d31329ae52b734683784c4b054839a661
  

On 11/9/21 16:30, Marek Polacek wrote:
> On Tue, Nov 09, 2021 at 02:17:14PM -0500, Marek Polacek wrote:
>> On Tue, Nov 09, 2021 at 12:27:28PM -0500, Jason Merrill wrote:
>>> On 11/9/21 10:55, Marek Polacek wrote:
>>>> On Tue, Nov 09, 2021 at 08:09:10AM +0100, Bernhard Reutner-Fischer wrote:
>>>>> On Tue, 9 Nov 2021 00:12:10 -0500
>>>>> Jason Merrill <jason@redhat.com> wrote:
>>>>>
>>>>>> On 11/8/21 20:41, Marek Polacek wrote:
>>>>>>> On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:
>>>>>
>>>>>>> +  for (auto opt : v)
>>>>>>> +    {
>>>>>>> +      char *cln = strstr (opt, "::");
>>>>>>> +      /* We don't accept '::attr'.  */
>>>>>>> +      if (cln == nullptr || cln == opt)
>>>>>>> +	{
>>>>>>> +	  error ("wrong argument to ignored attributes");
>>>>>>> +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
>>>>>>> +	  continue;
>>>>>>> +	}
>>>>>>> +      char *vendor_start = opt;
>>>>>>> +      ptrdiff_t vendor_len = cln - opt;
>>>>>>> +      char *attr_start = cln + 2;
>>>>>>> +      /* This could really use rawmemchr :(.  */
>>>>>>> +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
>>>>>>> +      /* Verify that they look valid.  */
>>>>>>> +      auto valid_p = [](const char *const s, ptrdiff_t len) {
>>>>>>> +	for (int i = 0; i < len; ++i)
>>>>>>> +	  if (!ISALNUM (*s) && *s != '_')
>>>>>>> +	    return false;
>>>>>>> +	return true;
>>>>>>> +      };
>>>>>>> +      if (!valid_p (vendor_start, vendor_len)
>>>>>>> +	  || !valid_p (attr_start, attr_len))
>>>>>>> +	{
>>>>>>> +	  error ("wrong argument to ignored attributes");
>>>>>>> +	  continue;
>>>>>>> +	}
>>>>>>> +      /* Turn "__attr__" into "attr" so that we have a canonical form of
>>>>>>> +	 attribute names.  Likewise for vendor.  */
>>>>>>> +      auto strip = [](char *&s, ptrdiff_t &l) {
>>>>>>> +	if (l > 4 && s[0] == '_' && s[1] == '_'
>>>>>>> +	    && s[l - 1] == '_' && s[l - 2] == '_')
>>>>>>> +	  {
>>>>>>> +	    s += 2;
>>>>>>> +	    l -= 4;
>>>>>>> +	  }
>>>>>>> +      };
>>>>>>> +      strip (attr_start, attr_len);
>>>>>>> +      strip (vendor_start, vendor_len);
>>>>>>> +      /* We perform all this hijinks so that we don't have to copy OPT.  */
>>>>>>> +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
>>>>>>> +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
>>>>>>> +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
>>>>>>> +	 register it twice would lead to a crash.  */
>>>>>>> +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
>>>>>>> +	continue;
>>>>>>
>>>>>> Hmm, this looks like it isn't handling the case of previously ignoring
>>>>>> vendor::; it seems we'll look for vendor::<empty string> instead, not
>>>>>> find it, and register again.
>>>
>>>> Yes, for -Wno-attributes=vendor::,vendor:: we call register_scoped_attributes
>>>> twice, but I think that's OK: register_scoped_attributes will see that
>>>> find_attribute_namespace finds the namespace and returns without
>>>> creating a new  one.
>>>>
>>>> I think the current code handles -Wno-attributes=vendor::a,vendor:: well so
>>>> I'm not sure if I should change it.
>>>
>>> Makes sense.  But we should be able to avoid calling
>>> lookup_scoped_attribute_spec, and even get_identifier_with_length (attr...),
>>> if attr_len is 0.
>>   
>> Duh, of course.  Also no need to canonicalize an empty string.
>>
>>>>> I don't know if there are __attrib with 2 leading underscores but no
>>>>> trailing that we accept and should normalize?
>>>>>
>>>>> And it is surprising that we do not have a simple normalize_attr_name().
>>>>> There must be existing spots where we would normalize attribute names?
>>>>> extract_attribute_substring does about the same but with a struct substring(?).
>>>>> Maybe that's just to avoid a normal string hash.
>>>>
>>>> We have canonicalize_attr_name which I based my code on.
>>>
>>> We could factor out of that function an overload equivalent to your strip
>>> lambda?
>>
>> OK.  Since it's taking a reference and I wanted it to work both with a size_t
>> and ptrdiff_t, I made it a template.  Is is too much?
> 
> OK, this time for real.  Here's another version, which doesn't crash on
> -Wno-attributes=c::____.  I apologize for the number of takes.  :-(
> 
> Bootstrap/regtest running on ppc64le-linux-gnu.  OK if it passes?

OK, thanks for your persistence.  :)

> -- >8 --
> It is desirable for -Wattributes to warn about e.g.
> 
> [[deprecate]] void g(); // typo, should warn
> 
> However, -Wattributes also warns about vendor-specific attributes
> (that's because lookup_scoped_attribute_spec -> find_attribute_namespace
> finds nothing), which, with -Werror, causes grief.  We don't want the
> -Wattributes warning for
> 
> [[company::attr]] void f();
> 
> GCC warns because it doesn't know the "company" namespace; it only knows
> the "gnu" and "omp" namespaces.  We could entirely disable warning about
> attributes in unknown scopes but then the compiler would also miss typos
> like
> 
>    [[company::attrx]] void f();
> 
> or
> 
>    [[gmu::warn_used_result]] int write();
> 
> so that is not a viable solution.  A workaround is to use a #pragma:
> 
>    #pragma GCC diagnostic push
>    #pragma GCC diagnostic ignored "-Wattributes"
>    [[company::attr]] void f() {}
>    #pragma GCC diagnostic pop
> 
> but that's a mouthful and awkward to use and could also hide typos.  In
> fact, any macro-based solution doesn't seem like a way forward.
> 
> This patch implements -Wno-attributes=, which takes these arguments:
> 
> company::attr
> company::
> 
> This option should go well with using @file: the user could have a file
> containing
> -Wno-attributes=vendor::attr1,vendor::attr2
> and then invoke gcc with '@attrs' or similar.
> 
> I've also added a new pragma which has the same effect:
> 
> The pragma along with the new option should help with various static
> analysis tools.
> 
> 	PR c++/101940
> 
> gcc/ChangeLog:
> 
> 	* attribs.c (struct scoped_attributes): Add a bool member.
> 	(lookup_scoped_attribute_spec): Forward declare.
> 	(register_scoped_attributes): New bool parameter, defaulted to
> 	false.  Use it.
> 	(handle_ignored_attributes_option): New function.
> 	(free_attr_data): New function.
> 	(init_attributes): Call handle_ignored_attributes_option.
> 	(attr_namespace_ignored_p): New function.
> 	(decl_attributes): Check attr_namespace_ignored_p before
> 	warning.
> 	* attribs.h (free_attr_data): Declare.
> 	(register_scoped_attributes): Adjust declaration.
> 	(handle_ignored_attributes_option): Declare.
> 	(canonicalize_attr_name): New function template.
> 	(canonicalize_attr_name): Use it.
> 	* common.opt (Wattributes=): New option with a variable.
> 	* doc/extend.texi: Document #pragma GCC diagnostic ignored_attributes.
> 	* doc/invoke.texi: Document -Wno-attributes=.
> 	* opts.c (common_handle_option) <case OPT_Wattributes_>: Handle.
> 	* plugin.h (register_scoped_attributes): Adjust declaration.
> 	* toplev.c (compile_file): Call free_attr_data.
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
> 	ignored_attributes.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* c-c++-common/Wno-attributes-1.c: New test.
> 	* c-c++-common/Wno-attributes-2.c: New test.
> 	* c-c++-common/Wno-attributes-3.c: New test.
> ---
>   gcc/attribs.c                                 | 127 +++++++++++++++++-
>   gcc/attribs.h                                 |  28 +++-
>   gcc/c-family/c-pragma.c                       |  37 ++++-
>   gcc/common.opt                                |   9 +-
>   gcc/doc/extend.texi                           |  19 +++
>   gcc/doc/invoke.texi                           |  20 +++
>   gcc/opts.c                                    |  20 +++
>   gcc/plugin.h                                  |   4 +-
>   gcc/testsuite/c-c++-common/Wno-attributes-1.c |  55 ++++++++
>   gcc/testsuite/c-c++-common/Wno-attributes-2.c |  56 ++++++++
>   gcc/testsuite/c-c++-common/Wno-attributes-3.c |   9 ++
>   gcc/toplev.c                                  |   2 +
>   12 files changed, 374 insertions(+), 12 deletions(-)
>   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-1.c
>   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-2.c
>   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-3.c
> 
> diff --git a/gcc/attribs.c b/gcc/attribs.c
> index 83fafc98b7d..0284e5bf2fd 100644
> --- a/gcc/attribs.c
> +++ b/gcc/attribs.c
> @@ -87,6 +87,8 @@ struct scoped_attributes
>     const char *ns;
>     vec<attribute_spec> attributes;
>     hash_table<attribute_hasher> *attribute_hash;
> +  /* True if we should not warn about unknown attributes in this NS.  */
> +  bool ignored_p;
>   };
>   
>   /* The table of scope attributes.  */
> @@ -95,6 +97,8 @@ static vec<scoped_attributes> attributes_table;
>   static scoped_attributes* find_attribute_namespace (const char*);
>   static void register_scoped_attribute (const struct attribute_spec *,
>   				       scoped_attributes *);
> +static const struct attribute_spec *lookup_scoped_attribute_spec (const_tree,
> +								  const_tree);
>   
>   static bool attributes_initialized = false;
>   
> @@ -121,12 +125,14 @@ extract_attribute_substring (struct substring *str)
>   
>   /* Insert an array of attributes ATTRIBUTES into a namespace.  This
>      array must be NULL terminated.  NS is the name of attribute
> -   namespace.  The function returns the namespace into which the
> -   attributes have been registered.  */
> +   namespace.  IGNORED_P is true iff all unknown attributes in this
> +   namespace should be ignored for the purposes of -Wattributes.  The
> +   function returns the namespace into which the attributes have been
> +   registered.  */
>   
>   scoped_attributes *
>   register_scoped_attributes (const struct attribute_spec *attributes,
> -			    const char *ns)
> +			    const char *ns, bool ignored_p /*=false*/)
>   {
>     scoped_attributes *result = NULL;
>   
> @@ -144,9 +150,12 @@ register_scoped_attributes (const struct attribute_spec *attributes,
>         memset (&sa, 0, sizeof (sa));
>         sa.ns = ns;
>         sa.attributes.create (64);
> +      sa.ignored_p = ignored_p;
>         result = attributes_table.safe_push (sa);
>         result->attribute_hash = new hash_table<attribute_hasher> (200);
>       }
> +  else
> +    result->ignored_p |= ignored_p;
>   
>     /* Really add the attributes to their namespace now.  */
>     for (unsigned i = 0; attributes[i].name != NULL; ++i)
> @@ -224,6 +233,99 @@ check_attribute_tables (void)
>   				 attribute_tables[j][l].name));
>   }
>   
> +/* Used to stash pointers to allocated memory so that we can free them at
> +   the end of parsing of all TUs. */
> +static vec<attribute_spec *> ignored_attributes_table;
> +
> +/* Parse arguments V of -Wno-attributes=.
> +   Currently we accept:
> +     vendor::attr
> +     vendor::
> +   This functions also registers the parsed attributes so that we don't
> +   warn that we don't recognize them.  */
> +
> +void
> +handle_ignored_attributes_option (vec<char *> *v)
> +{
> +  if (v == nullptr)
> +    return;
> +
> +  for (auto opt : v)
> +    {
> +      char *cln = strstr (opt, "::");
> +      /* We don't accept '::attr'.  */
> +      if (cln == nullptr || cln == opt)
> +	{
> +	  error ("wrong argument to ignored attributes");
> +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> +	  continue;
> +	}
> +      const char *vendor_start = opt;
> +      ptrdiff_t vendor_len = cln - opt;
> +      const char *attr_start = cln + 2;
> +      /* This could really use rawmemchr :(.  */
> +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
> +      /* Verify that they look valid.  */
> +      auto valid_p = [](const char *const s, ptrdiff_t len) {
> +	bool ok = false;
> +
> +	for (int i = 0; i < len; ++i)
> +	  if (ISALNUM (s[i]))
> +	    ok = true;
> +	  else if (s[i] != '_')
> +	    return false;
> +
> +	return ok;
> +      };
> +      if (!valid_p (vendor_start, vendor_len))
> +	{
> +	  error ("wrong argument to ignored attributes");
> +	  continue;
> +	}
> +      canonicalize_attr_name (vendor_start, vendor_len);
> +      /* We perform all this hijinks so that we don't have to copy OPT.  */
> +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
> +      const char *attr;
> +      /* In the "vendor::" case, we should ignore *any* attribute coming
> +	 from this attribute namespace.  */
> +      if (attr_len > 0)
> +	{
> +	  if (!valid_p (attr_start, attr_len))
> +	    {
> +	      error ("wrong argument to ignored attributes");
> +	      continue;
> +	    }
> +	  canonicalize_attr_name (attr_start, attr_len);
> +	  tree attr_id = get_identifier_with_length (attr_start, attr_len);
> +	  attr = IDENTIFIER_POINTER (attr_id);
> +	  /* If we've already seen this vendor::attr, ignore it.  Attempting to
> +	     register it twice would lead to a crash.  */
> +	  if (lookup_scoped_attribute_spec (vendor_id, attr_id))
> +	    continue;
> +	}
> +      else
> +	attr = nullptr;
> +      /* Create a table with extra attributes which we will register.
> +	 We can't free it here, so squirrel away the pointers.  */
> +      attribute_spec *table = new attribute_spec[2];
> +      ignored_attributes_table.safe_push (table);
> +      table[0] = { attr, 0, 0, false, false, false, false, nullptr, nullptr };
> +      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr,
> +		   nullptr };
> +      register_scoped_attributes (table, IDENTIFIER_POINTER (vendor_id), !attr);
> +    }
> +}
> +
> +/* Free data we might have allocated when adding extra attributes.  */
> +
> +void
> +free_attr_data ()
> +{
> +  for (auto x : ignored_attributes_table)
> +    delete[] x;
> +  ignored_attributes_table.release ();
> +}
> +
>   /* Initialize attribute tables, and make some sanity checks if checking is
>      enabled.  */
>   
> @@ -252,6 +354,9 @@ init_attributes (void)
>       /* Put all the GNU attributes into the "gnu" namespace.  */
>       register_scoped_attributes (attribute_tables[i], "gnu");
>   
> +  vec<char *> *ignored = (vec<char *> *) flag_ignored_attributes;
> +  handle_ignored_attributes_option (ignored);
> +
>     invoke_plugin_callbacks (PLUGIN_ATTRIBUTES, NULL);
>     attributes_initialized = true;
>   }
> @@ -456,6 +561,19 @@ diag_attr_exclusions (tree last_decl, tree node, tree attrname,
>     return found;
>   }
>   
> +/* Return true iff we should not complain about unknown attributes
> +   coming from the attribute namespace NS.  This is the case for
> +   the -Wno-attributes=ns:: command-line option.  */
> +
> +static bool
> +attr_namespace_ignored_p (tree ns)
> +{
> +  if (ns == NULL_TREE)
> +    return false;
> +  scoped_attributes *r = find_attribute_namespace (IDENTIFIER_POINTER (ns));
> +  return r && r->ignored_p;
> +}
> +
>   /* Process the attributes listed in ATTRIBUTES and install them in *NODE,
>      which is either a DECL (including a TYPE_DECL) or a TYPE.  If a DECL,
>      it should be modified in place; if a TYPE, a copy should be created
> @@ -556,7 +674,8 @@ decl_attributes (tree *node, tree attributes, int flags,
>   
>         if (spec == NULL)
>   	{
> -	  if (!(flags & (int) ATTR_FLAG_BUILT_IN))
> +	  if (!(flags & (int) ATTR_FLAG_BUILT_IN)
> +	      && !attr_namespace_ignored_p (ns))
>   	    {
>   	      if (ns == NULL_TREE || !cxx11_attr_p)
>   		warning (OPT_Wattributes, "%qE attribute directive ignored",
> diff --git a/gcc/attribs.h b/gcc/attribs.h
> index 138c509bce1..ba657881940 100644
> --- a/gcc/attribs.h
> +++ b/gcc/attribs.h
> @@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
>   #define GCC_ATTRIBS_H
>   
>   extern const struct attribute_spec *lookup_attribute_spec (const_tree);
> +extern void free_attr_data ();
>   extern void init_attributes (void);
>   
>   /* Process the attributes listed in ATTRIBUTES and install them in *NODE,
> @@ -40,12 +41,14 @@ extern void apply_tm_attr (tree, tree);
>   extern tree make_attribute (const char *, const char *, tree);
>   
>   extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
> -							     const char *);
> +							     const char *,
> +							     bool = false);
>   
>   extern char *sorted_attr_string (tree);
>   extern bool common_function_versions (tree, tree);
>   extern tree make_dispatcher_decl (const tree);
>   extern bool is_function_default_version (const tree);
> +extern void handle_ignored_attributes_option (vec<char *> *);
>   
>   /* Return a type like TTYPE except that its TYPE_ATTRIBUTES
>      is ATTRIBUTE.
> @@ -114,17 +117,34 @@ extern unsigned decls_mismatched_attributes (tree, tree, tree,
>   
>   extern void maybe_diag_alias_attributes (tree, tree);
>   
> +/* For a given string S of length L, strip leading and trailing '_' characters
> +   so that we have a canonical form of attribute names.  NB: This function may
> +   change S and L.  */
> +
> +template <typename T>
> +inline bool
> +canonicalize_attr_name (const char *&s, T &l)
> +{
> +  if (l > 4 && s[0] == '_' && s[1] == '_' && s[l - 1] == '_' && s[l - 2] == '_')
> +    {
> +      s += 2;
> +      l -= 4;
> +      return true;
> +    }
> +  return false;
> +}
> +
>   /* For a given IDENTIFIER_NODE, strip leading and trailing '_' characters
>      so that we have a canonical form of attribute names.  */
>   
>   static inline tree
>   canonicalize_attr_name (tree attr_name)
>   {
> -  const size_t l = IDENTIFIER_LENGTH (attr_name);
> +  size_t l = IDENTIFIER_LENGTH (attr_name);
>     const char *s = IDENTIFIER_POINTER (attr_name);
>   
> -  if (l > 4 && s[0] == '_' && s[1] == '_' && s[l - 1] == '_' && s[l - 2] == '_')
> -    return get_identifier_with_length (s + 2, l - 4);
> +  if (canonicalize_attr_name (s, l))
> +    return get_identifier_with_length (s, l);
>   
>     return attr_name;
>   }
> diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
> index a9be8df0384..a299ceff6a2 100644
> --- a/gcc/c-family/c-pragma.c
> +++ b/gcc/c-family/c-pragma.c
> @@ -764,7 +764,7 @@ handle_pragma_diagnostic(cpp_reader *ARG_UNUSED(dummy))
>     if (token != CPP_NAME)
>       {
>         warning_at (loc, OPT_Wpragmas,
> -		  "missing [error|warning|ignored|push|pop]"
> +		  "missing [error|warning|ignored|push|pop|ignored_attributes]"
>   		  " after %<#pragma GCC diagnostic%>");
>         return;
>       }
> @@ -787,10 +787,43 @@ handle_pragma_diagnostic(cpp_reader *ARG_UNUSED(dummy))
>         diagnostic_pop_diagnostics (global_dc, input_location);
>         return;
>       }
> +  else if (strcmp (kind_string, "ignored_attributes") == 0)
> +    {
> +      token = pragma_lex (&x, &loc);
> +      if (token != CPP_STRING)
> +	{
> +	  warning_at (loc, OPT_Wpragmas,
> +		      "missing attribute name after %<#pragma GCC diagnostic "
> +		      "ignored_attributes%>");
> +	  return;
> +	}
> +      char *args = xstrdup (TREE_STRING_POINTER (x));
> +      const size_t l = strlen (args);
> +      if (l == 0)
> +	{
> +	  warning_at (loc, OPT_Wpragmas, "missing argument to %<#pragma GCC "
> +		      "diagnostic ignored_attributes%>");
> +	  free (args);
> +	  return;
> +	}
> +      else if (args[l - 1] == ',')
> +	{
> +	  warning_at (loc, OPT_Wpragmas, "trailing %<,%> in arguments for "
> +		      "%<#pragma GCC diagnostic ignored_attributes%>");
> +	  free (args);
> +	  return;
> +	}
> +      auto_vec<char *> v;
> +      for (char *p = strtok (args, ","); p; p = strtok (NULL, ","))
> +	v.safe_push (p);
> +      handle_ignored_attributes_option (&v);
> +      free (args);
> +      return;
> +    }
>     else
>       {
>         warning_at (loc, OPT_Wpragmas,
> -		  "expected [error|warning|ignored|push|pop]"
> +		  "expected [error|warning|ignored|push|pop|ignored_attributes]"
>   		  " after %<#pragma GCC diagnostic%>");
>         return;
>       }
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 1a5b9bfcca9..de9b848eda5 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -83,7 +83,7 @@ int flag_gen_aux_info = 0
>   Variable
>   int flag_shlib
>   
> -; These two are really VEC(char_p,heap) *.
> +; These three are really VEC(char_p,heap) *.
>   
>   Variable
>   void *flag_instrument_functions_exclude_functions
> @@ -91,6 +91,9 @@ void *flag_instrument_functions_exclude_functions
>   Variable
>   void *flag_instrument_functions_exclude_files
>   
> +Variable
> +void *flag_ignored_attributes
> +
>   ; Generic structs (e.g. templates not explicitly specialized)
>   ; may not have a compilation unit associated with them, and so
>   ; may need to be treated differently from ordinary structs.
> @@ -549,6 +552,10 @@ Wattributes
>   Common Var(warn_attributes) Init(1) Warning
>   Warn about inappropriate attribute usage.
>   
> +Wattributes=
> +Common Joined
> +Do not warn about specified attributes.
> +
>   Wattribute-alias
>   Common Alias(Wattribute_alias=, 1, 0) Warning
>   Warn about type safety and similar errors and mismatches in declarations with alias attributes.
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index eee4c6737bb..6e6c580e329 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -23767,6 +23767,25 @@ restored.
>     foo(d);                       /* depends on command-line options */
>   @end smallexample
>   
> +@item #pragma GCC diagnostic ignored_attributes
> +
> +Similarly to @option{-Wno-attributes=}, this pragma allows users to suppress
> +warnings about unknown scoped attributes (in C++11 and C2X).  For example,
> +@code{#pragma GCC diagnostic ignored_attributes "vendor::attr"} disables
> +warning about the following declaration:
> +
> +@smallexample
> +[[vendor::attr]] void f();
> +@end smallexample
> +
> +whereas @code{#pragma GCC diagnostic ignored_attributes "vendor::"} prevents
> +warning about both of these declarations:
> +
> +@smallexample
> +[[vendor::safe]] void f();
> +[[vendor::unsafe]] void f2();
> +@end smallexample
> +
>   @end table
>   
>   GCC also offers a simple mechanism for printing messages during
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 2ea23d07c4c..297ca98deae 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -8707,6 +8707,26 @@ unrecognized attributes, function attributes applied to variables,
>   etc.  This does not stop errors for incorrect use of supported
>   attributes.
>   
> +Additionally, using @option{-Wno-attributes=}, it is possible to suppress
> +warnings about unknown scoped attributes (in C++11 and C2X).  For example,
> +@option{-Wno-attributes=vendor::attr} disables warning about the following
> +declaration:
> +
> +@smallexample
> +[[vendor::attr]] void f();
> +@end smallexample
> +
> +It is also possible to disable warning about all attributes in a namespace
> +using @option{-Wno-attributes=vendor::} which prevents warning about both
> +of these declarations:
> +
> +@smallexample
> +[[vendor::safe]] void f();
> +[[vendor::unsafe]] void f2();
> +@end smallexample
> +
> +Note that @option{-Wno-attributes=} does not imply @option{-Wno-attributes}.
> +
>   @item -Wno-builtin-declaration-mismatch
>   @opindex Wno-builtin-declaration-mismatch
>   @opindex Wbuiltin-declaration-mismatch
> diff --git a/gcc/opts.c b/gcc/opts.c
> index caed6255500..175b4635bb4 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -2611,6 +2611,26 @@ common_handle_option (struct gcc_options *opts,
>         /* Currently handled in a prescan.  */
>         break;
>   
> +    case OPT_Wattributes_:
> +      if (lang_mask == CL_DRIVER)
> +	break;
> +
> +      if (value)
> +	{
> +	  error_at (loc, "arguments ignored for %<-Wattributes=%>; use "
> +		    "%<-Wno-attributes=%> instead");
> +	  break;
> +	}
> +      else if (arg[strlen (arg) - 1] == ',')
> +	{
> +	  error_at (loc, "trailing %<,%> in arguments for "
> +		    "%<-Wno-attributes=%>");
> +	  break;
> +	}
> +
> +      add_comma_separated_to_vector (&opts->x_flag_ignored_attributes, arg);
> +      break;
> +
>       case OPT_Werror:
>         dc->warning_as_error_requested = value;
>         break;
> diff --git a/gcc/plugin.h b/gcc/plugin.h
> index 1640e253ca5..5556763d1bf 100644
> --- a/gcc/plugin.h
> +++ b/gcc/plugin.h
> @@ -197,7 +197,9 @@ invoke_plugin_callbacks (int event ATTRIBUTE_UNUSED,
>   /* In attribs.c.  */
>   
>   extern void register_attribute (const struct attribute_spec *attr);
> +/* The default argument for the third parameter is given in attribs.h.  */
>   extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
> -							     const char *);
> +							     const char *,
> +							     bool);
>   
>   #endif /* PLUGIN_H */
> diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-1.c b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
> new file mode 100644
> index 00000000000..aac1a69fd85
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
> @@ -0,0 +1,55 @@
> +/* PR c++/101940 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "-std=c++11" { target c++ } } */
> +/* { dg-additional-options "-Wno-attributes=company::,yoyodyne::attr" } */
> +/* { dg-additional-options "-Wno-attributes=c1::attr,c1::attr,c1::__attr__" } */
> +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
> +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
> +/* { dg-additional-options "-Wno-attributes=x::" } */
> +/* { dg-additional-options "-Wno-attributes=yoyodyne::attr_new" } */
> +/* { dg-additional-options "-Wno-attributes=c4::__attr__" } */
> +/* { dg-additional-options "-Wno-attributes=c5::attr" } */
> +/* { dg-additional-options "-Wno-attributes=__c6__::attr" } */
> +
> +[[company::attr]] void f1();
> +[[company::attr2]] void f2();
> +
> +[[yoyodyne::attr]] void f3();
> +[[yoyodyne::__attr__]] void f3__();
> +[[yoyodyne::attrx]] void f4(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attrx__]] void f4__(); /* { dg-warning "ignored" } */
> +
> +[[c1::attr]] void f5();
> +
> +[[c2::attr]] void f6();
> +[[c2::attrx]] void f7();
> +[[c2::__attr__]] void f6__();
> +[[c2::__attrx__]] void f7__();
> +
> +[[c3::attr]] void f8();
> +[[c3::attrx]] void f9();
> +
> +[[x::x]] void f10();
> +
> +[[yoyodyne::attr_new]] void f11();
> +[[yoyodyne::__attr_new__]] void f11__();
> +[[yoyodyne::attr_mew]] void f12(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attr_mew__]] void f12__(); /* { dg-warning "ignored" } */
> +
> +[[c4::attr]] void f13();
> +[[c4::__attr__]] void f13__();
> +[[c4::attrx]] void f14(); /* { dg-warning "ignored" } */
> +
> +[[c5::attr]] void f15();
> +[[c5::__attr__]] void f15__();
> +[[__c5__::attr]] void __f15();
> +[[__c5__::__attr__]] void __f15__();
> +[[c5::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +[[__c5__::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +
> +[[c6::attr]] void f16();
> +[[c6::__attr__]] void f16__();
> +[[__c6__::attr]] void __f16();
> +[[__c6__::__attr__]] void __f16__();
> +[[c6::attrx]] void f16x(); /* { dg-warning "ignored" } */
> +[[__c6__::attrx]] void f16x(); /* { dg-warning "ignored" } */
> diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-2.c b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
> new file mode 100644
> index 00000000000..4307c74b048
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
> @@ -0,0 +1,56 @@
> +/* PR c++/101940 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "-std=c++11" { target c++ } } */
> +
> +#pragma GCC diagnostic ignored_attributes "company::,yoyodyne::attr"
> +#pragma GCC diagnostic ignored_attributes "c1::attr,c1::attr,c1::__attr__"
> +#pragma GCC diagnostic ignored_attributes "c2::,c2::attr"
> +#pragma GCC diagnostic ignored_attributes "c3::attr,c3::"
> +#pragma GCC diagnostic ignored_attributes "x::"
> +#pragma GCC diagnostic ignored_attributes "yoyodyne::attr_new"
> +#pragma GCC diagnostic ignored_attributes "c4::__attr__"
> +#pragma GCC diagnostic ignored_attributes "c5::attr"
> +#pragma GCC diagnostic ignored_attributes "__c6__::attr"
> +
> +[[company::attr]] void f1();
> +[[company::attr2]] void f2();
> +
> +[[yoyodyne::attr]] void f3();
> +[[yoyodyne::__attr__]] void f3__();
> +[[yoyodyne::attrx]] void f4(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attrx__]] void f4__(); /* { dg-warning "ignored" } */
> +
> +[[c1::attr]] void f5();
> +
> +[[c2::attr]] void f6();
> +[[c2::attrx]] void f7();
> +[[c2::__attr__]] void f6__();
> +[[c2::__attrx__]] void f7__();
> +
> +[[c3::attr]] void f8();
> +[[c3::attrx]] void f9();
> +
> +[[x::x]] void f10();
> +
> +[[yoyodyne::attr_new]] void f11();
> +[[yoyodyne::__attr_new__]] void f11__();
> +[[yoyodyne::attr_mew]] void f12(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attr_mew__]] void f12__(); /* { dg-warning "ignored" } */
> +
> +[[c4::attr]] void f13();
> +[[c4::__attr__]] void f13__();
> +[[c4::attrx]] void f14(); /* { dg-warning "ignored" } */
> +
> +[[c5::attr]] void f15();
> +[[c5::__attr__]] void f15__();
> +[[__c5__::attr]] void __f15();
> +[[__c5__::__attr__]] void __f15__();
> +[[c5::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +[[__c5__::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +
> +[[c6::attr]] void f16();
> +[[c6::__attr__]] void f16__();
> +[[__c6__::attr]] void __f16();
> +[[__c6__::__attr__]] void __f16__();
> +[[c6::attrx]] void f16x(); /* { dg-warning "ignored" } */
> +[[__c6__::attrx]] void f16x(); /* { dg-warning "ignored" } */
> diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-3.c b/gcc/testsuite/c-c++-common/Wno-attributes-3.c
> new file mode 100644
> index 00000000000..64370f2ef6f
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-3.c
> @@ -0,0 +1,9 @@
> +/* PR c++/101940 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "-Wno-attributes=___::" } */
> +/* { dg-additional-options "-Wno-attributes=c::____" } */
> +/* { dg-additional-options "-Wno-attributes=____::____" } */
> +/* { dg-additional-options "-Wno-attributes=c@::attr" } */
> +/* { dg-additional-options "-Wno-attributes=c2::@tr" } */
> +
> +/* { dg-error "wrong argument to ignored attributes" "" { target *-*-* } 0 } */
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index e91f083f8ff..99276bde87d 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -457,6 +457,8 @@ compile_file (void)
>     if (flag_dump_locations)
>       dump_location_info (stderr);
>   
> +  free_attr_data ();
> +
>     /* Compilation is now finished except for writing
>        what's left of the symbol table output.  */
>   
> 
> base-commit: 8875a92d31329ae52b734683784c4b054839a661
>