c++: Fix up pedantic handling of alignas [PR110345]

The following patch on top of the PR110345 P2552R3 series
emits pedantic pedwarns for alignas appertaining to incorrect entities.
As the middle-end and attribute exclusions look for "aligned" attribute,
the patch transforms alignas into "internal "::aligned attribute (didn't
use [[aligned (x)]] so that people can't type it that way).

2024-12-18  Jakub Jelinek  <jakub@redhat.com>

	PR c++/110345
gcc/c-family/
	* c-common.h (attr_aligned_exclusions): Declare.
	(handle_aligned_attribute): Likewise.
	* c-attribs.cc (handle_aligned_attribute): No longer
	static.
	(attr_aligned_exclusions): Use extern instead of static.
gcc/cp/
	* cp-tree.h (enum cp_tree_index): Add CPTI_INTERNAL_IDENTIFIER.
	(internal_identifier): Define.
	(internal_attribute_table): Declare.
	* parser.cc (cp_parser_exception_declaration): Error on alignas
	on exception declaration.
	(cp_parser_std_attribute_spec): Turn alignas into internal
	ns aligned attribute rather than gnu.
	* decl.cc (initialize_predefined_identifiers): Initialize
	internal_identifier.
	* tree.cc (handle_alignas_attribute): New function.
	(internal_attributes): New variable.
	(internal_attribute_table): Likewise.
	* cp-objcp-common.h (cp_objcp_attribute_table): Add
	internal_attribute_table entry.
gcc/testsuite/
	* g++.dg/cpp0x/alignas1.C: Add dg-options "".
	* g++.dg/cpp0x/alignas2.C: Likewise.
	* g++.dg/cpp0x/alignas7.C: Likewise.
	* g++.dg/cpp0x/alignas21.C: New test.
	* g++.dg/ext/bitfield9.C: Expect a warning.
	* g++.dg/cpp2a/is-layout-compatible3.C: Add dg-options -pedantic.
	Expect a warning.

2 files changed, 4 insertions, 3 deletions

diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index eb76a9e..3bb2cb5 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -101,7 +101,6 @@ static tree handle_destructor_attribute (tree *, tree, tree, int, bool *);
 static tree handle_mode_attribute (tree *, tree, tree, int, bool *);
 static tree handle_section_attribute (tree *, tree, tree, int, bool *);
 static tree handle_special_var_sec_attribute (tree *, tree, tree, int, bool *);
-static tree handle_aligned_attribute (tree *, tree, tree, int, bool *);
 static tree handle_warn_if_not_aligned_attribute (tree *, tree, tree,
 						  int, bool *);
 static tree handle_strict_flex_array_attribute (tree *, tree, tree,
@@ -195,7 +194,7 @@ static tree handle_null_terminated_string_arg_attribute (tree *, tree, tree, int
   { name, function, type, variable }
 
 /* Define attributes that are mutually exclusive with one another.  */
-static const struct attribute_spec::exclusions attr_aligned_exclusions[] =
+extern const struct attribute_spec::exclusions attr_aligned_exclusions[] =
 {
   /* Attribute name     exclusion applies to:
 	                function, type, variable */
@@ -2816,7 +2815,7 @@ common_handle_aligned_attribute (tree *node, tree name, tree args, int flags,
 /* Handle a "aligned" attribute; arguments as in
    struct attribute_spec.handler.  */
 
-static tree
+tree
 handle_aligned_attribute (tree *node, tree name, tree args,
 			  int flags, bool *no_add_attrs)
 {
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index ac574e9..13406e2 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1666,8 +1666,10 @@ extern int parse_tm_stmt_attr (tree, int);
 extern int tm_attr_to_mask (tree);
 extern tree tm_mask_to_attr (int);
 extern tree find_tm_attribute (tree);
+extern const struct attribute_spec::exclusions attr_aligned_exclusions[];
 extern const struct attribute_spec::exclusions attr_cold_hot_exclusions[];
 extern const struct attribute_spec::exclusions attr_noreturn_exclusions[];
+extern tree handle_aligned_attribute (tree *, tree, tree, int, bool *);
 extern tree handle_noreturn_attribute (tree *, tree, tree, int, bool *);
 extern tree handle_musttail_attribute (tree *, tree, tree, int, bool *);
 extern bool has_attribute (location_t, tree, tree, tree (*)(tree));