diff mbox series

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

Message ID 20210920170658.28014-1-polacek@redhat.com
State New
Headers show
Series attribs: Implement -Wno-attributes=vendor::attr [PR101940] | expand

Commit Message

Marek Polacek Sept. 20, 2021, 5:06 p.m. UTC
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::
clang

The last one is a special option to ignore clang-only attributes; in
this patch it is accepted but currently has no effect.

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.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	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.
	* 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.

gcc/c-family/ChangeLog:

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

gcc/c/ChangeLog:

	* c-decl.c (c_parse_final_cleanups): Call free_attr_data.

gcc/cp/ChangeLog:

	* decl2.c (c_parse_final_cleanups): Call free_attr_data.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-1.c: New test.
	* c-c++-common/Wno-attributes-2.c: New test.
---
 gcc/attribs.c                                 | 122 +++++++++++++++++-
 gcc/attribs.h                                 |   5 +-
 gcc/c-family/c-pragma.c                       |  22 +++-
 gcc/c/c-decl.c                                |   2 +
 gcc/common.opt                                |   9 +-
 gcc/cp/decl2.c                                |   2 +
 gcc/doc/extend.texi                           |  19 +++
 gcc/doc/invoke.texi                           |  18 +++
 gcc/opts.c                                    |  14 ++
 gcc/plugin.h                                  |   4 +-
 gcc/testsuite/c-c++-common/Wno-attributes-1.c |  40 ++++++
 gcc/testsuite/c-c++-common/Wno-attributes-2.c |  41 ++++++
 12 files changed, 289 insertions(+), 9 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


base-commit: 1949d7540a0322993bcae2f8893e2dbd29209040

Comments

Jakub Jelinek Sept. 20, 2021, 5:38 p.m. UTC | #1
On Mon, Sep 20, 2021 at 01:06:58PM -0400, Marek Polacek via Gcc-patches wrote:

Not a review, just a few nits:

I think it would be useful to clarify that -Wno-attributes=list doesn't
actually imply -Wno-attributes

> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -88,6 +88,9 @@ 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.
> @@ -546,6 +549,10 @@ Wattributes
>  Common Var(warn_attributes) Init(1) Warning
>  Warn about inappropriate attribute usage.
>  
> +Wattributes=
> +Common Joined
> +Do not warn about specified attributes.
> +

So, wouldn't be this better specified as
Wno-attributes=
Common Joined RejectNegative
(not sure if RejectNegative is actually needed for an option
starting with Wno- )?

> +/* { 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=clang" } */
> +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
> +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
> +/* { dg-additional-options "-Wno-attributes=x::," } */

Should the above be accepted (I mean trailing , ?)  What does that mean?

> +/* { dg-additional-options "-Wno-attributes=yoyodyne::attr_new" } */
> +/* { dg-additional-options "-Wno-attributes=c4::__attr__" } */

When writing __attr__, does that imply we won't warn about both
c4::attr and c4::__attr__ (and __c4__::attr and __c4__::__attr__) like
it would when writing -Wno-attributes=c4::attr ?

	Jakub
Marek Polacek Sept. 20, 2021, 6:37 p.m. UTC | #2
On Mon, Sep 20, 2021 at 07:38:59PM +0200, Jakub Jelinek wrote:
> On Mon, Sep 20, 2021 at 01:06:58PM -0400, Marek Polacek via Gcc-patches wrote:
> 
> Not a review, just a few nits:
> 
> I think it would be useful to clarify that -Wno-attributes=list doesn't
> actually imply -Wno-attributes

Agreed, fixed with:

+Note that @option{-Wno-attributes=} does not imply @option{-Wno-attributes}.
 
> > --- a/gcc/common.opt
> > +++ b/gcc/common.opt
> > @@ -88,6 +88,9 @@ 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.
> > @@ -546,6 +549,10 @@ Wattributes
> >  Common Var(warn_attributes) Init(1) Warning
> >  Warn about inappropriate attribute usage.
> >  
> > +Wattributes=
> > +Common Joined
> > +Do not warn about specified attributes.
> > +
> 
> So, wouldn't be this better specified as
> Wno-attributes=
> Common Joined RejectNegative
> (not sure if RejectNegative is actually needed for an option
> starting with Wno- )?

Looks like RejectNegative is not needed.  I could do that, but I think
it regresses the diagnostic:

error: unrecognized command-line option '-Wattributes=attr::'
vs
error: arguments ignored for ‘-Wattributes=’; use ‘-Wno-attributes=’ instead

I prefer the latter.  (I've changed the warning into error.)
 
> > +/* { 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=clang" } */
> > +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
> > +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
> > +/* { dg-additional-options "-Wno-attributes=x::," } */
> 
> Should the above be accepted (I mean trailing , ?)  What does that mean?
 
I'm thinking it should: the arguments to -Wno-attributes= could be
generated by a tool so accepting the trailing , might help, like in
enums etc.

> > +/* { dg-additional-options "-Wno-attributes=yoyodyne::attr_new" } */
> > +/* { dg-additional-options "-Wno-attributes=c4::__attr__" } */
> 
> When writing __attr__, does that imply we won't warn about both
> c4::attr and c4::__attr__ (and __c4__::attr and __c4__::__attr__) like
> it would when writing -Wno-attributes=c4::attr ?

"__attr__" and "attr" ought to be interchangeable.  __c4__:: and c4:: currently
are not, but I guess they should.  I'll post a v2 with that fixed.

Thanks!
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
Marek Polacek Sept. 20, 2021, 7:03 p.m. UTC | #3
On Mon, Sep 20, 2021 at 02:37:03PM -0400, Marek Polacek wrote:
> > > +/* { dg-additional-options "-Wno-attributes=yoyodyne::attr_new" } */
> > > +/* { dg-additional-options "-Wno-attributes=c4::__attr__" } */
> > 
> > When writing __attr__, does that imply we won't warn about both
> > c4::attr and c4::__attr__ (and __c4__::attr and __c4__::__attr__) like
> > it would when writing -Wno-attributes=c4::attr ?
> 
> "__attr__" and "attr" ought to be interchangeable.  __c4__:: and c4:: currently
> are not, but I guess they should.  I'll post a v2 with that fixed.

Here's v2 with the documentation enhancement, warning -> error, and
which handles __vendor__:: the same as vendor::.

Regtest/bootstrap running.

-- >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::
clang

The last one is a special option to ignore clang-only attributes; in
this patch it is accepted but currently has no effect.

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.
	* 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.

gcc/c-family/ChangeLog:

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

gcc/c/ChangeLog:

	* c-decl.c (c_parse_final_cleanups): Call free_attr_data.

gcc/cp/ChangeLog:

	* decl2.c (c_parse_final_cleanups): Call free_attr_data.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-1.c: New test.
	* c-c++-common/Wno-attributes-2.c: New test.
---
 gcc/attribs.c                                 | 126 +++++++++++++++++-
 gcc/attribs.h                                 |   5 +-
 gcc/c-family/c-pragma.c                       |  22 ++-
 gcc/c/c-decl.c                                |   2 +
 gcc/common.opt                                |   9 +-
 gcc/cp/decl2.c                                |   2 +
 gcc/doc/extend.texi                           |  19 +++
 gcc/doc/invoke.texi                           |  20 +++
 gcc/opts.c                                    |  14 ++
 gcc/plugin.h                                  |   4 +-
 gcc/testsuite/c-c++-common/Wno-attributes-1.c |  56 ++++++++
 gcc/testsuite/c-c++-common/Wno-attributes-2.c |  57 ++++++++
 12 files changed, 327 insertions(+), 9 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

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 83fafc98b7d..869006e3526 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 +233,98 @@ 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 ARGS of -Wno-attributes=.
+   Currently we accept:
+     vendor::attr
+     vendor::
+   and as a special case:
+     clang
+   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)
+    {
+      if (strcmp (opt, "clang") == 0)
+	{
+	  // TODO
+	  continue;
+	}
+      char *q = strstr (opt, "::");
+      /* We don't accept '::attr'.  */
+      if (q == nullptr || q == opt)
+	{
+	  error ("wrong argument to ignored attributes");
+	  inform (input_location, "valid format is %<ns::attr%>, %<ns::%>, "
+		  "or %<clang%>");
+	  continue;
+	}
+      /* Cut off the vendor part.  */
+      *q = '\0';
+      char *vendor = opt;
+      char *attr = q + 2;
+      /* Verify that they look valid.  */
+      auto valid_p = [](const char *s) {
+	for (; *s != '\0'; ++s)
+	  if (!ISALNUM (*s) && *s != '_')
+	    return false;
+	return true;
+      };
+      if (!valid_p (vendor) || !valid_p (attr))
+	{
+	  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) {
+	const size_t l = strlen (s);
+	if (l > 4 && s[0] == '_' && s[1] == '_'
+	    && s[l - 1] == '_' && s[l - 2] == '_')
+	  {
+	    s[l - 2] = '\0';
+	    s += 2;
+	  }
+      };
+      strip (attr);
+      strip (vendor);
+      /* 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 (get_identifier (vendor),
+					get_identifier (attr)))
+	continue;
+      /* In the "vendor::" case, we should ignore *any* attribute coming
+	 from this attribute namespace.  */
+      const bool ignored_ns = attr[0] == '\0';
+      /* 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] = { ignored_ns ? nullptr : attr, 0, 0, false, false,
+		   false, false, nullptr, nullptr };
+      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr, nullptr };
+      register_scoped_attributes (table, vendor, ignored_ns);
+    }
+}
+
+/* Free data we might have allocated when adding extra attributes.  */
+
+void
+free_attr_data ()
+{
+  for (auto x : ignored_attributes_table)
+    delete[] x;
+}
+
 /* Initialize attribute tables, and make some sanity checks if checking is
    enabled.  */
 
@@ -252,6 +353,9 @@ 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 +560,19 @@ 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 +673,8 @@ 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..96a527f67a9 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.
diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
index a9be8df0384..3f7b8380d93 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 +787,28 @@ 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));
+      auto_vec<char *> v;
+      for (char *p = strtok (args, ","); p; p = strtok (NULL, ","))
+	v.safe_push (p);
+      handle_ignored_attributes_option (&v);
+      /* ??? We can't free (args); here.  */
+      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/c/c-decl.c b/gcc/c/c-decl.c
index 771efa3eadf..345c8f9d620 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -12295,6 +12295,8 @@ c_parse_final_cleanups (void)
     c_write_global_declarations_1 (BLOCK_VARS (DECL_INITIAL (t)));
   c_write_global_declarations_1 (BLOCK_VARS (ext_block));
 
+  free_attr_data ();
+
   if (!in_lto_p)
     free_attr_access_data ();
 
diff --git a/gcc/common.opt b/gcc/common.opt
index b921f5e3b25..0da1d714819 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -80,7 +80,7 @@ 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
@@ -88,6 +88,9 @@ 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.
@@ -546,6 +549,10 @@ 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/cp/decl2.c b/gcc/cp/decl2.c
index a79a70ba9c2..58388c51dab 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -5305,6 +5305,8 @@ c_parse_final_cleanups (void)
   cp_tree_c_finish_parsing ();
   clear_consteval_vfns (consteval_vtables);
 
+  free_attr_data ();
+
   /* The entire file is now complete.  If requested, dump everything
      to a file.  */
   dump_tu ();
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 9501a60f20e..48eaf16d209 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -23745,6 +23745,25 @@ 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 4acb94181d2..2b0ec511984 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8621,6 +8621,26 @@ 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 1d2d22d7a3f..2e5d42cea72 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2546,6 +2546,20 @@ 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;
+	}
+
+      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..4ecee1bd9e4
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
@@ -0,0 +1,56 @@
+/* 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=clang" } */
+/* { 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..b635befcc37
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
@@ -0,0 +1,57 @@
+/* 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 "clang"
+#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" } */

base-commit: 1949d7540a0322993bcae2f8893e2dbd29209040
Jakub Jelinek Sept. 20, 2021, 7:08 p.m. UTC | #4
On Mon, Sep 20, 2021 at 02:37:03PM -0400, Marek Polacek wrote:
> > So, wouldn't be this better specified as
> > Wno-attributes=
> > Common Joined RejectNegative
> > (not sure if RejectNegative is actually needed for an option
> > starting with Wno- )?
> 
> Looks like RejectNegative is not needed.  I could do that, but I think
> it regresses the diagnostic:
> 
> error: unrecognized command-line option '-Wattributes=attr::'
> vs
> error: arguments ignored for ‘-Wattributes=’; use ‘-Wno-attributes=’ instead
> 
> I prefer the latter.  (I've changed the warning into error.)

Ok.

> > > +/* { 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=clang" } */
> > > +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
> > > +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
> > > +/* { dg-additional-options "-Wno-attributes=x::," } */
> > 
> > Should the above be accepted (I mean trailing , ?)  What does that mean?
>  
> I'm thinking it should: the arguments to -Wno-attributes= could be
> generated by a tool so accepting the trailing , might help, like in
> enums etc.

I don't think we allow that for any other options that accept a list of
something (except maybe -W{p,c,a,l}, those just pass the args through).
Generating a list that has comma separation only in between items and not
at the end is trivial.

	Jakub
Marek Polacek Sept. 20, 2021, 10:59 p.m. UTC | #5
On Mon, Sep 20, 2021 at 09:08:09PM +0200, Jakub Jelinek wrote:
> On Mon, Sep 20, 2021 at 02:37:03PM -0400, Marek Polacek wrote:
> > > So, wouldn't be this better specified as
> > > Wno-attributes=
> > > Common Joined RejectNegative
> > > (not sure if RejectNegative is actually needed for an option
> > > starting with Wno- )?
> > 
> > Looks like RejectNegative is not needed.  I could do that, but I think
> > it regresses the diagnostic:
> > 
> > error: unrecognized command-line option '-Wattributes=attr::'
> > vs
> > error: arguments ignored for ‘-Wattributes=’; use ‘-Wno-attributes=’ instead
> > 
> > I prefer the latter.  (I've changed the warning into error.)
> 
> Ok.
> 
> > > > +/* { 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=clang" } */
> > > > +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
> > > > +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
> > > > +/* { dg-additional-options "-Wno-attributes=x::," } */
> > > 
> > > Should the above be accepted (I mean trailing , ?)  What does that mean?
> >  
> > I'm thinking it should: the arguments to -Wno-attributes= could be
> > generated by a tool so accepting the trailing , might help, like in
> > enums etc.
> 
> I don't think we allow that for any other options that accept a list of
> something (except maybe -W{p,c,a,l}, those just pass the args through).
> Generating a list that has comma separation only in between items and not
> at the end is trivial.

Hmm, ok, here's a version with that checking added.  Sadly it needs
to be handled before handle_ignored_attributes_option because of
strtok.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >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::
clang

The last one is a special option to ignore clang-only attributes; in
this patch it is accepted but currently has no effect.

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.
	* 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.

gcc/c-family/ChangeLog:

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

gcc/c/ChangeLog:

	* c-decl.c (c_parse_final_cleanups): Call free_attr_data.

gcc/cp/ChangeLog:

	* decl2.c (c_parse_final_cleanups): Call free_attr_data.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-1.c: New test.
	* c-c++-common/Wno-attributes-2.c: New test.
---
 gcc/attribs.c                                 | 126 +++++++++++++++++-
 gcc/attribs.h                                 |   5 +-
 gcc/c-family/c-pragma.c                       |  37 ++++-
 gcc/c/c-decl.c                                |   2 +
 gcc/common.opt                                |   9 +-
 gcc/cp/decl2.c                                |   2 +
 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 |  56 ++++++++
 gcc/testsuite/c-c++-common/Wno-attributes-2.c |  57 ++++++++
 12 files changed, 348 insertions(+), 9 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

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 83fafc98b7d..869006e3526 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 +233,98 @@ 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 ARGS of -Wno-attributes=.
+   Currently we accept:
+     vendor::attr
+     vendor::
+   and as a special case:
+     clang
+   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)
+    {
+      if (strcmp (opt, "clang") == 0)
+	{
+	  // TODO
+	  continue;
+	}
+      char *q = strstr (opt, "::");
+      /* We don't accept '::attr'.  */
+      if (q == nullptr || q == opt)
+	{
+	  error ("wrong argument to ignored attributes");
+	  inform (input_location, "valid format is %<ns::attr%>, %<ns::%>, "
+		  "or %<clang%>");
+	  continue;
+	}
+      /* Cut off the vendor part.  */
+      *q = '\0';
+      char *vendor = opt;
+      char *attr = q + 2;
+      /* Verify that they look valid.  */
+      auto valid_p = [](const char *s) {
+	for (; *s != '\0'; ++s)
+	  if (!ISALNUM (*s) && *s != '_')
+	    return false;
+	return true;
+      };
+      if (!valid_p (vendor) || !valid_p (attr))
+	{
+	  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) {
+	const size_t l = strlen (s);
+	if (l > 4 && s[0] == '_' && s[1] == '_'
+	    && s[l - 1] == '_' && s[l - 2] == '_')
+	  {
+	    s[l - 2] = '\0';
+	    s += 2;
+	  }
+      };
+      strip (attr);
+      strip (vendor);
+      /* 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 (get_identifier (vendor),
+					get_identifier (attr)))
+	continue;
+      /* In the "vendor::" case, we should ignore *any* attribute coming
+	 from this attribute namespace.  */
+      const bool ignored_ns = attr[0] == '\0';
+      /* 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] = { ignored_ns ? nullptr : attr, 0, 0, false, false,
+		   false, false, nullptr, nullptr };
+      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr, nullptr };
+      register_scoped_attributes (table, vendor, ignored_ns);
+    }
+}
+
+/* Free data we might have allocated when adding extra attributes.  */
+
+void
+free_attr_data ()
+{
+  for (auto x : ignored_attributes_table)
+    delete[] x;
+}
+
 /* Initialize attribute tables, and make some sanity checks if checking is
    enabled.  */
 
@@ -252,6 +353,9 @@ 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 +560,19 @@ 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 +673,8 @@ 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..96a527f67a9 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.
diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
index a9be8df0384..6beba5503f0 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);
+      /* ??? We can't free (args); here.  */
+      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/c/c-decl.c b/gcc/c/c-decl.c
index 771efa3eadf..345c8f9d620 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -12295,6 +12295,8 @@ c_parse_final_cleanups (void)
     c_write_global_declarations_1 (BLOCK_VARS (DECL_INITIAL (t)));
   c_write_global_declarations_1 (BLOCK_VARS (ext_block));
 
+  free_attr_data ();
+
   if (!in_lto_p)
     free_attr_access_data ();
 
diff --git a/gcc/common.opt b/gcc/common.opt
index b921f5e3b25..0da1d714819 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -80,7 +80,7 @@ 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
@@ -88,6 +88,9 @@ 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.
@@ -546,6 +549,10 @@ 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/cp/decl2.c b/gcc/cp/decl2.c
index a79a70ba9c2..58388c51dab 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -5305,6 +5305,8 @@ c_parse_final_cleanups (void)
   cp_tree_c_finish_parsing ();
   clear_consteval_vfns (consteval_vtables);
 
+  free_attr_data ();
+
   /* The entire file is now complete.  If requested, dump everything
      to a file.  */
   dump_tu ();
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 9501a60f20e..48eaf16d209 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -23745,6 +23745,25 @@ 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 4acb94181d2..2b0ec511984 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8621,6 +8621,26 @@ 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 1d2d22d7a3f..ba664a515a2 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2546,6 +2546,26 @@ 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..c174eef5fba
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
@@ -0,0 +1,56 @@
+/* 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=clang" } */
+/* { 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..8e9f55ea2da
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
@@ -0,0 +1,57 @@
+/* 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 "clang"
+#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" } */

base-commit: b333c3acb8d436b256ba8922c6426c93860bb616
Jason Merrill Sept. 23, 2021, 6:25 p.m. UTC | #6
On 9/20/21 18:59, Marek Polacek via Gcc-patches wrote:
> On Mon, Sep 20, 2021 at 09:08:09PM +0200, Jakub Jelinek wrote:
>> On Mon, Sep 20, 2021 at 02:37:03PM -0400, Marek Polacek wrote:
>>>> So, wouldn't be this better specified as
>>>> Wno-attributes=
>>>> Common Joined RejectNegative
>>>> (not sure if RejectNegative is actually needed for an option
>>>> starting with Wno- )?
>>>
>>> Looks like RejectNegative is not needed.  I could do that, but I think
>>> it regresses the diagnostic:
>>>
>>> error: unrecognized command-line option '-Wattributes=attr::'
>>> vs
>>> error: arguments ignored for ‘-Wattributes=’; use ‘-Wno-attributes=’ instead
>>>
>>> I prefer the latter.  (I've changed the warning into error.)
>>
>> Ok.
>>
>>>>> +/* { 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=clang" } */
>>>>> +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
>>>>> +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
>>>>> +/* { dg-additional-options "-Wno-attributes=x::," } */
>>>>
>>>> Should the above be accepted (I mean trailing , ?)  What does that mean?
>>>   
>>> I'm thinking it should: the arguments to -Wno-attributes= could be
>>> generated by a tool so accepting the trailing , might help, like in
>>> enums etc.
>>
>> I don't think we allow that for any other options that accept a list of
>> something (except maybe -W{p,c,a,l}, those just pass the args through).
>> Generating a list that has comma separation only in between items and not
>> at the end is trivial.
> 
> Hmm, ok, here's a version with that checking added.  Sadly it needs
> to be handled before handle_ignored_attributes_option because of
> strtok.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> -- >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::
> clang
> 
> The last one is a special option to ignore clang-only attributes; in
> this patch it is accepted but currently has no effect.
> 
> 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.
> 	* 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.
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
> 	ignored_attributes.
> 
> gcc/c/ChangeLog:
> 
> 	* c-decl.c (c_parse_final_cleanups): Call free_attr_data.
> 
> gcc/cp/ChangeLog:
> 
> 	* decl2.c (c_parse_final_cleanups): Call free_attr_data.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* c-c++-common/Wno-attributes-1.c: New test.
> 	* c-c++-common/Wno-attributes-2.c: New test.
> ---
>   gcc/attribs.c                                 | 126 +++++++++++++++++-
>   gcc/attribs.h                                 |   5 +-
>   gcc/c-family/c-pragma.c                       |  37 ++++-
>   gcc/c/c-decl.c                                |   2 +
>   gcc/common.opt                                |   9 +-
>   gcc/cp/decl2.c                                |   2 +
>   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 |  56 ++++++++
>   gcc/testsuite/c-c++-common/Wno-attributes-2.c |  57 ++++++++
>   12 files changed, 348 insertions(+), 9 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
> 
> diff --git a/gcc/attribs.c b/gcc/attribs.c
> index 83fafc98b7d..869006e3526 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 +233,98 @@ 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 ARGS of -Wno-attributes=.
> +   Currently we accept:
> +     vendor::attr
> +     vendor::
> +   and as a special case:
> +     clang
> +   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)
> +    {
> +      if (strcmp (opt, "clang") == 0)
> +	{
> +	  // TODO
> +	  continue;
> +	}

If this doesn't work yet, let's not accept it at all for now.

> +      char *q = strstr (opt, "::");
> +      /* We don't accept '::attr'.  */
> +      if (q == nullptr || q == opt)
> +	{
> +	  error ("wrong argument to ignored attributes");
> +	  inform (input_location, "valid format is %<ns::attr%>, %<ns::%>, "
> +		  "or %<clang%>");

...or even mention it.  Users can ignore clang:: instead, it doesn't 
matter to us if clang attributes are misspelled.

> +	  continue;
> +	}
> +      /* Cut off the vendor part.  */
> +      *q = '\0';
> +      char *vendor = opt;
> +      char *attr = q + 2;
> +      /* Verify that they look valid.  */
> +      auto valid_p = [](const char *s) {
> +	for (; *s != '\0'; ++s)
> +	  if (!ISALNUM (*s) && *s != '_')
> +	    return false;
> +	return true;
> +      };
> +      if (!valid_p (vendor) || !valid_p (attr))
> +	{
> +	  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) {
> +	const size_t l = strlen (s);
> +	if (l > 4 && s[0] == '_' && s[1] == '_'
> +	    && s[l - 1] == '_' && s[l - 2] == '_')
> +	  {
> +	    s[l - 2] = '\0';
> +	    s += 2;
> +	  }
> +      };
> +      strip (attr);
> +      strip (vendor);
> +      /* 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 (get_identifier (vendor),
> +					get_identifier (attr)))
> +	continue;
> +      /* In the "vendor::" case, we should ignore *any* attribute coming
> +	 from this attribute namespace.  */
> +      const bool ignored_ns = attr[0] == '\0';

Maybe set attr to nullptr instead of declaring ignored_ns?

> +      /* 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] = { ignored_ns ? nullptr : attr, 0, 0, false, false,

...so this can just use attr.

> +		   false, false, nullptr, nullptr };
> +      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr, nullptr };
> +      register_scoped_attributes (table, vendor, ignored_ns);
> +    }
> +}
> +
> +/* Free data we might have allocated when adding extra attributes.  */
> +
> +void
> +free_attr_data ()
> +{
> +  for (auto x : ignored_attributes_table)
> +    delete[] x;
> +}

You probably also want to zero out ignored_attributes_table at this point.

>   /* Initialize attribute tables, and make some sanity checks if checking is
>      enabled.  */
>   
> @@ -252,6 +353,9 @@ 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 +560,19 @@ 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 +673,8 @@ 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..96a527f67a9 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.
> diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
> index a9be8df0384..6beba5503f0 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);
> +      /* ??? We can't free (args); here.  */

Perhaps we want to copy strings in handle_ignored_attributes_option 
rather than here?

> +      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/c/c-decl.c b/gcc/c/c-decl.c
> index 771efa3eadf..345c8f9d620 100644
> --- a/gcc/c/c-decl.c
> +++ b/gcc/c/c-decl.c
> @@ -12295,6 +12295,8 @@ c_parse_final_cleanups (void)
>       c_write_global_declarations_1 (BLOCK_VARS (DECL_INITIAL (t)));
>     c_write_global_declarations_1 (BLOCK_VARS (ext_block));
>   
> +  free_attr_data ();

Since handle_ignored_attributes_option is in language-independent code, 
shouldn't this call be as well?

>     if (!in_lto_p)
>       free_attr_access_data ();
>   
> diff --git a/gcc/common.opt b/gcc/common.opt
> index b921f5e3b25..0da1d714819 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -80,7 +80,7 @@ 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
> @@ -88,6 +88,9 @@ 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.
> @@ -546,6 +549,10 @@ 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/cp/decl2.c b/gcc/cp/decl2.c
> index a79a70ba9c2..58388c51dab 100644
> --- a/gcc/cp/decl2.c
> +++ b/gcc/cp/decl2.c
> @@ -5305,6 +5305,8 @@ c_parse_final_cleanups (void)
>     cp_tree_c_finish_parsing ();
>     clear_consteval_vfns (consteval_vtables);
>   
> +  free_attr_data ();
> +
>     /* The entire file is now complete.  If requested, dump everything
>        to a file.  */
>     dump_tu ();
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 9501a60f20e..48eaf16d209 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -23745,6 +23745,25 @@ 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 4acb94181d2..2b0ec511984 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -8621,6 +8621,26 @@ 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 1d2d22d7a3f..ba664a515a2 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -2546,6 +2546,26 @@ 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..c174eef5fba
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
> @@ -0,0 +1,56 @@
> +/* 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=clang" } */
> +/* { 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..8e9f55ea2da
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
> @@ -0,0 +1,57 @@
> +/* 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 "clang"
> +#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" } */
> 
> base-commit: b333c3acb8d436b256ba8922c6426c93860bb616
>
diff mbox series

Patch

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 83fafc98b7d..c85f3aedc4d 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 +233,94 @@  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 ARGS of -Wno-attributes=.
+   Currently we accept:
+     vendor::attr
+     vendor::
+   and as a special case:
+     clang
+   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)
+    {
+      if (strcmp (opt, "clang") == 0)
+	{
+	  // TODO
+	  continue;
+	}
+      char *q = strstr (opt, "::");
+      /* We don't accept '::attr'.  */
+      if (q == nullptr || q == opt)
+	{
+	  error ("wrong argument to ignored attributes");
+	  inform (input_location, "valid format is %<ns::attr%>, %<ns::%>, "
+		  "or %<clang%>");
+	  continue;
+	}
+      /* Cut off the vendor part.  */
+      *q = '\0';
+      const char *vendor = opt;
+      char *attr = q + 2;
+      /* Verify that they look valid.  */
+      auto valid_p = [](const char *s) {
+	for (; *s != '\0'; ++s)
+	  if (!ISALNUM (*s) && *s != '_')
+	    return false;
+	return true;
+      };
+      if (!valid_p (vendor) || !valid_p (attr))
+	{
+	  error ("wrong argument to ignored attributes");
+	  continue;
+	}
+      /* Turn "__attr__" into "attr" so that we have a canonical form of
+	 attribute names.  */
+      const size_t l = strlen (attr);
+      if (l > 4 && attr[0] == '_' && attr[1] == '_'
+	  && attr[l - 1] == '_' && attr[l - 2] == '_')
+	{
+	  attr[l - 2] = '\0';
+	  attr += 2;
+	}
+      /* 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 (get_identifier (vendor),
+					get_identifier (attr)))
+	continue;
+      /* In the "vendor::" case, we should ignore *any* attribute coming
+	 from this attribute namespace.  */
+      const bool ignored_ns = attr[0] == '\0';
+      /* 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] = { ignored_ns ? nullptr : attr, 0, 0, false, false,
+		   false, false, nullptr, nullptr };
+      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr, nullptr };
+      register_scoped_attributes (table, vendor, ignored_ns);
+    }
+}
+
+/* Free data we might have allocated when adding extra attributes.  */
+
+void
+free_attr_data ()
+{
+  for (auto x : ignored_attributes_table)
+    delete[] x;
+}
+
 /* Initialize attribute tables, and make some sanity checks if checking is
    enabled.  */
 
@@ -252,6 +349,9 @@  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 +556,19 @@  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 +669,8 @@  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..96a527f67a9 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.
diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
index a9be8df0384..3f7b8380d93 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 +787,28 @@  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));
+      auto_vec<char *> v;
+      for (char *p = strtok (args, ","); p; p = strtok (NULL, ","))
+	v.safe_push (p);
+      handle_ignored_attributes_option (&v);
+      /* ??? We can't free (args); here.  */
+      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/c/c-decl.c b/gcc/c/c-decl.c
index 771efa3eadf..345c8f9d620 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -12295,6 +12295,8 @@  c_parse_final_cleanups (void)
     c_write_global_declarations_1 (BLOCK_VARS (DECL_INITIAL (t)));
   c_write_global_declarations_1 (BLOCK_VARS (ext_block));
 
+  free_attr_data ();
+
   if (!in_lto_p)
     free_attr_access_data ();
 
diff --git a/gcc/common.opt b/gcc/common.opt
index b921f5e3b25..0da1d714819 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -80,7 +80,7 @@  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
@@ -88,6 +88,9 @@  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.
@@ -546,6 +549,10 @@  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/cp/decl2.c b/gcc/cp/decl2.c
index a79a70ba9c2..58388c51dab 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -5305,6 +5305,8 @@  c_parse_final_cleanups (void)
   cp_tree_c_finish_parsing ();
   clear_consteval_vfns (consteval_vtables);
 
+  free_attr_data ();
+
   /* The entire file is now complete.  If requested, dump everything
      to a file.  */
   dump_tu ();
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 9501a60f20e..48eaf16d209 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -23745,6 +23745,25 @@  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 4acb94181d2..7c7241cdb88 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8621,6 +8621,24 @@  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
+
 @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 1d2d22d7a3f..45db0de3f2e 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2546,6 +2546,20 @@  common_handle_option (struct gcc_options *opts,
       /* Currently handled in a prescan.  */
       break;
 
+    case OPT_Wattributes_:
+      if (lang_mask == CL_DRIVER)
+	break;
+
+      if (value)
+	{
+	  warning_at (loc, 0, "arguments ignored for %<-Wattributes=%>; use "
+		      "%<-Wno-attributes=%> instead");
+	  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..e28f1fbab17
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
@@ -0,0 +1,40 @@ 
+/* 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=clang" } */
+/* { 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__" } */
+
+[[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" } */
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..1b08e972aed
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
@@ -0,0 +1,41 @@ 
+/* 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 "clang"
+#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__"
+
+[[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" } */