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

--- gcc/c-family/c-common.h.jj	2024-09-06 13:43:37.311307920 +0200
+++ gcc/c-family/c-common.h	2024-09-06 15:33:47.497616169 +0200
@@ -1645,8 +1645,10 @@  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));
--- gcc/c-family/c-attribs.cc.jj	2024-09-06 13:43:37.300308064 +0200
+++ gcc/c-family/c-attribs.cc	2024-09-06 16:00:55.864465359 +0200
@@ -100,7 +100,6 @@  static tree handle_destructor_attribute
 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,
@@ -192,7 +191,7 @@  static tree handle_null_terminated_strin
   { 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 */
@@ -2806,7 +2805,7 @@  common_handle_aligned_attribute (tree *n
 /* 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)
 {
--- gcc/cp/cp-tree.h.jj	2024-09-06 13:58:09.428940803 +0200
+++ gcc/cp/cp-tree.h	2024-09-06 15:51:23.012904756 +0200
@@ -192,6 +192,7 @@  enum cp_tree_index
     CPTI_HEAP_VEC_UNINIT_IDENTIFIER,
     CPTI_HEAP_VEC_IDENTIFIER,
     CPTI_OMP_IDENTIFIER,
+    CPTI_INTERNAL_IDENTIFIER,
 
     CPTI_LANG_NAME_C,
     CPTI_LANG_NAME_CPLUSPLUS,
@@ -345,6 +346,7 @@  extern GTY(()) tree cp_global_trees[CPTI
 #define heap_vec_uninit_identifier	cp_global_trees[CPTI_HEAP_VEC_UNINIT_IDENTIFIER]
 #define heap_vec_identifier		cp_global_trees[CPTI_HEAP_VEC_IDENTIFIER]
 #define omp_identifier			cp_global_trees[CPTI_OMP_IDENTIFIER]
+#define internal_identifier		cp_global_trees[CPTI_INTERNAL_IDENTIFIER]
 #define lang_name_c			cp_global_trees[CPTI_LANG_NAME_C]
 #define lang_name_cplusplus		cp_global_trees[CPTI_LANG_NAME_CPLUSPLUS]
 
@@ -8132,6 +8134,7 @@  extern bool is_byte_access_type			(tree)
 extern bool is_byte_access_type_not_plain_char	(tree);
 extern const struct scoped_attribute_specs cxx_gnu_attribute_table;
 extern const struct scoped_attribute_specs std_attribute_table;
+extern const struct scoped_attribute_specs internal_attribute_table;
 extern tree make_ptrmem_cst			(tree, tree);
 extern tree cp_build_type_attribute_variant     (tree, tree);
 extern tree cp_build_reference_type		(tree, bool);
--- gcc/cp/parser.cc.jj	2024-09-06 14:29:48.392322139 +0200
+++ gcc/cp/parser.cc	2024-09-06 17:10:18.507455975 +0200
@@ -29681,7 +29681,15 @@  cp_parser_exception_declaration (cp_pars
   tree decl = grokdeclarator (declarator, &type_specifiers, CATCHPARM, 1,
 			      &type_specifiers.attributes);
   if (decl != error_mark_node && type_specifiers.attributes)
-    cplus_decl_attributes (&decl, type_specifiers.attributes, 0);
+    {
+      cplus_decl_attributes (&decl, type_specifiers.attributes, 0);
+      if (pedantic && lookup_attribute ("internal ", "aligned",
+					DECL_ATTRIBUTES (decl)))
+	pedwarn (type_specifiers.locations[ds_attribute]
+		 ? type_specifiers.locations[ds_attribute]
+		 : input_location, OPT_Wpedantic,
+		 "%<alignas%> on exception declaration");
+    }
 
   return decl;
 }
@@ -31131,7 +31139,7 @@  cp_parser_std_attribute_spec (cp_parser
       /* Build the C++-11 representation of an 'aligned'
 	 attribute.  */
       attributes
-	= build_tree_list (build_tree_list (gnu_identifier,
+	= build_tree_list (build_tree_list (internal_identifier,
 					    aligned_identifier), alignas_expr);
     }
 
--- gcc/cp/decl.cc.jj	2024-09-06 14:29:32.619526092 +0200
+++ gcc/cp/decl.cc	2024-09-06 15:51:53.437509531 +0200
@@ -4812,6 +4812,7 @@  initialize_predefined_identifiers (void)
     {"heap [] uninit", &heap_vec_uninit_identifier, cik_normal},
     {"heap []", &heap_vec_identifier, cik_normal},
     {"omp", &omp_identifier, cik_normal},
+    {"internal ", &internal_identifier, cik_normal},
     {NULL, NULL, cik_normal}
   };
 
--- gcc/cp/tree.cc.jj	2024-09-06 14:30:05.278103789 +0200
+++ gcc/cp/tree.cc	2024-09-06 17:16:47.490434844 +0200
@@ -5127,6 +5127,35 @@  handle_maybe_unused_attribute (tree *nod
   return ret;
 }
 
+/* The C++11 alignment specifier.  It mostly maps to GNU aligned attribute,
+   but we need to do some extra pedantic checking.  */
+
+static tree
+handle_alignas_attribute (tree *node, tree name, tree args, int flags,
+			  bool *no_add_attrs)
+{
+  tree t = *node;
+  tree ret = handle_aligned_attribute (node, name, args, flags, no_add_attrs);
+  if (pedantic)
+    {
+      if (TREE_CODE (*node) == FUNCTION_DECL)
+	pedwarn (input_location, OPT_Wattributes,
+		 "%<alignas%> on function declaration");
+      else if (TREE_CODE (*node) == ENUMERAL_TYPE)
+	pedwarn (input_location, OPT_Wattributes,
+		 "%<alignas%> on enumerated type");
+      else if (TYPE_P (*node) && t != *node)
+	pedwarn (input_location, OPT_Wattributes,
+		 "%<alignas%> on a type other than class");
+      else if (TREE_CODE (*node) == FIELD_DECL && DECL_C_BIT_FIELD (*node))
+	pedwarn (input_location, OPT_Wattributes, "%<alignas%> on bit-field");
+      else if (TREE_CODE (t) == TYPE_DECL)
+	pedwarn (input_location, OPT_Wattributes,
+		 "%<alignas%> on a type alias");
+    }
+  return ret;
+}
+
 /* Table of valid C++ attributes.  */
 static const attribute_spec cxx_gnu_attributes[] =
 {
@@ -5177,6 +5206,18 @@  const scoped_attribute_specs std_attribu
   nullptr, { std_attributes }
 };
 
+/* Table of internal attributes.  */
+static const attribute_spec internal_attributes[] =
+{
+  { "aligned", 0, 1, false, false, false, false,
+    handle_alignas_attribute, attr_aligned_exclusions }
+};
+
+const scoped_attribute_specs internal_attribute_table =
+{
+  "internal ", { internal_attributes }
+};
+
 /* Handle an "init_priority" attribute; arguments as in
    struct attribute_spec.handler.  */
 static tree
--- gcc/cp/cp-objcp-common.h.jj	2024-09-06 13:43:37.712302692 +0200
+++ gcc/cp/cp-objcp-common.h	2024-09-06 15:47:33.425887161 +0200
@@ -129,7 +129,8 @@  static const scoped_attribute_specs *con
   &cxx_gnu_attribute_table,
   &c_common_gnu_attribute_table,
   &c_common_clang_attribute_table,
-  &c_common_format_attribute_table
+  &c_common_format_attribute_table,
+  &internal_attribute_table
 };
 
 #undef LANG_HOOKS_ATTRIBUTE_TABLE
--- gcc/testsuite/g++.dg/cpp0x/alignas1.C.jj	2020-01-12 11:54:37.052403768 +0100
+++ gcc/testsuite/g++.dg/cpp0x/alignas1.C	2024-09-06 17:22:09.014284498 +0200
@@ -1,5 +1,6 @@ 
 // PR c++/65734
 // { dg-do compile { target c++11 } }
+// { dg-options "" }
 
 template <class T> struct A
 {
--- gcc/testsuite/g++.dg/cpp0x/alignas2.C.jj	2020-01-12 11:54:37.052403768 +0100
+++ gcc/testsuite/g++.dg/cpp0x/alignas2.C	2024-09-06 17:22:36.848925193 +0200
@@ -1,5 +1,6 @@ 
 // PR c++/65734
 // { dg-do compile { target c++11 } }
+// { dg-options "" }
 
 template <typename T>
 struct BVector
--- gcc/testsuite/g++.dg/cpp0x/alignas7.C.jj	2020-01-12 11:54:37.052403768 +0100
+++ gcc/testsuite/g++.dg/cpp0x/alignas7.C	2024-09-06 17:23:02.934588031 +0200
@@ -1,5 +1,6 @@ 
 // PR c++/71513
 // { dg-do compile { target c++11 } }
+// { dg-options "" }
 
 template < int N, typename T >
 struct A
--- gcc/testsuite/g++.dg/cpp0x/alignas21.C.jj	2024-09-06 14:30:31.548763706 +0200
+++ gcc/testsuite/g++.dg/cpp0x/alignas21.C	2024-09-06 17:18:20.721231386 +0200
@@ -0,0 +1,157 @@ 
+// C++ 26 P2552R3 - On the ignorability of standard attributes
+// { dg-do compile { target c++11 } }
+
+int arr[2];
+struct S { int a, b; };
+S arr2[2];
+
+void
+foo (int n)
+{
+  alignas (int) int x1;
+  alignas ("foobar") int x2;			// { dg-error "'alignas' argument has non-integral type 'const char \\\[7\\\]'" }
+  alignas (0) int x3;				// { dg-warning "requested alignment '0' is not a positive power of 2" }
+  alignas ("foo", "bar", "baz") int x4;		// { dg-error "'alignas' argument has non-integral type 'const char \\\[4\\\]'" }
+						// { dg-error "expected '\\\)' before ',' token" "" { target *-*-* } .-1 }
+						// { dg-error "expected declaration before ',' token" "" { target *-*-* } .-2 }
+						// { dg-error "expected primary-expression before ',' token" "" { target *-*-* } .-3 }
+  alignas (0, 1, 2) int x5;			// { dg-error "expected '\\\)' before ',' token" }
+						// { dg-error "expected declaration before ',' token" "" { target *-*-* } .-1 }
+						// { dg-error "expected primary-expression before ',' token" "" { target *-*-* } .-2 }
+
+  auto a = [] alignas (int) () {};		// { dg-error "'alignas' on function declaration" }
+  auto b = [] constexpr alignas (int) {};	// { dg-error "'alignas' on a type other than class" }
+						// { dg-error "parameter declaration before lambda declaration specifiers only optional with" "" { target c++20_down } .-1 }
+						// { dg-error "'constexpr' lambda only available with" "" { target c++14_down } .-2 }
+  auto c = [] noexcept alignas (int) {};	// { dg-error "'alignas' on a type other than class" }
+						// { dg-error "parameter declaration before lambda exception specification only optional with" "" { target c++20_down } .-1 }
+  auto d = [] () alignas (int) {};		// { dg-error "'alignas' on a type other than class" }
+  auto e = new int [n] alignas (int);		// { dg-warning "attributes ignored on outermost array type in new expression" }
+  auto e2 = new int [n] alignas (int) [42];	// { dg-warning "attributes ignored on outermost array type in new expression" }
+  auto f = new int [n][42] alignas (int);	// { dg-error "'alignas' on a type other than class" }
+  alignas (int);				// { dg-warning "attributes at the beginning of statement are ignored" }
+  alignas (int) {}				// { dg-warning "attributes at the beginning of statement are ignored" }
+  alignas (int) if (true) {}			// { dg-warning "attributes at the beginning of statement are ignored" }
+  alignas (int) while (false) {}		// { dg-warning "attributes at the beginning of statement are ignored" }
+  alignas (int) goto lab;			// { dg-warning "attributes at the beginning of statement are ignored" }
+  alignas (int) lab:;				// { dg-error "alignment may not be specified for 'lab'" }
+  alignas (int) try {} catch (int) {}		// { dg-warning "attributes at the beginning of statement are ignored" }
+  if (alignas (int) int x = 0) {}
+  switch (n)
+    {
+    alignas (int) case 1:			// { dg-error "alignment may not be specified for" }
+    alignas (int) break;			// { dg-warning "attributes at the beginning of statement are ignored" }
+    alignas (int) default:			// { dg-error "alignment may not be specified for" }
+	 break;
+    }
+  for (alignas (int) auto a : arr) {}
+  for (alignas (int) auto [a, b] : arr2) {}	// { dg-error "structured bindings only available with" "" { target c++14_down } }
+  alignas (int) asm ("");			// { dg-warning "attributes ignored on 'asm' declaration" }
+  try {} catch (alignas (int) int x) {}		// { dg-error "'alignas' on exception declaration" }
+  try {} catch (alignas (int) int) {}		// { dg-error "'alignas' on exception declaration" }
+  try {} catch (int alignas (int) x) {}		// { dg-warning "attribute ignored" }
+  try {} catch (int alignas (int)) {}		// { dg-warning "attribute ignored" }
+  try {} catch (int x alignas (int)) {}		// { dg-error "'alignas' on exception declaration" }
+}
+
+alignas (int) int bar ();			// { dg-error "'alignas' on function declaration" }
+using foobar alignas (int) = int;		// { dg-error "'alignas' on a type alias" }
+alignas (int) int a;
+alignas (int) auto [b, c] = arr;		// { dg-error "structured bindings only available with" "" { target c++14_down } }
+alignas (int);					// { dg-warning "attribute ignored" }
+inline alignas (int) void baz () {}		// { dg-warning "attribute ignored" }
+						// { dg-error "standard attributes in middle of decl-specifiers" "" { target *-*-* } .-1 }
+constexpr alignas (int) int qux () { return 0; }	// { dg-warning "attribute ignored" }
+						// { dg-error "standard attributes in middle of decl-specifiers" "" { target *-*-* } .-1 }
+int alignas (int) d;				// { dg-warning "attribute ignored" }
+int const alignas (int) e = 1;			// { dg-warning "attribute ignored" }
+struct A {} alignas (int);			// { dg-warning "attribute ignored in declaration of 'struct A'" }
+struct A alignas (int);				// { dg-warning "attribute ignored" }
+struct A alignas (int) a1;			// { dg-warning "attribute ignored" }
+A alignas (int) a2;				// { dg-warning "attribute ignored" }
+enum B { B0 } alignas (int);			// { dg-warning "attribute ignored in declaration of 'enum B'" }
+enum B alignas (int);				// { dg-warning "attribute ignored" }
+enum B alignas (int) b1;			// { dg-warning "attribute ignored" }
+B alignas (int) b2;				// { dg-warning "attribute ignored" }
+struct alignas (int) C {};
+int f alignas (int);
+struct alignas (int) Y;
+int g[2] alignas (int);				// { dg-error "'alignas' on a type other than class" }
+int g2 alignas (int) [2];
+int corge () alignas (int);			// { dg-error "'alignas' on a type other than class" }
+int *alignas (int) h;				// { dg-error "'alignas' on a type other than class" }
+int & alignas (int) i = f;			// { dg-error "'alignas' on a type other than class" }
+int && alignas (int) j = 0;			// { dg-error "'alignas' on a type other than class" }
+int S::* alignas (int) k;			// { dg-error "'alignas' on a type other than class" }
+auto l = sizeof (int [2] alignas (int));	// { dg-error "'alignas' on a type other than class" }
+int freddy (alignas (int) int a,		// { dg-error "alignment may not be specified for 'a'" }
+	    alignas (int) int,			// { dg-error "alignment may not be specified for '<anonymous>'" }
+	    alignas (int) int c = 0,		// { dg-error "alignment may not be specified for 'c'" }
+	    alignas (int) int = 0);		// { dg-error "alignment may not be specified for '<anonymous>'" }
+void
+corge (alignas (int) int a,			// { dg-error "alignment may not be specified for 'a'" }
+       alignas (int) int,			// { dg-error "alignment may not be specified for '<anonymous>'" }
+       alignas (int) int c = 0,			// { dg-error "alignment may not be specified for 'c'" }
+       alignas (int) int = 0)			// { dg-error "alignment may not be specified for '<anonymous>'" }
+{
+}
+alignas (int) void
+garply ()					// { dg-error "'alignas' on function declaration" }
+{
+}
+int grault (int alignas (int) a,		// { dg-warning "attribute ignored" }
+	    int alignas (int),			// { dg-warning "attribute ignored" }
+	    int alignas (int) c = 0,		// { dg-warning "attribute ignored" }
+	    int alignas (int) = 0);		// { dg-warning "attribute ignored" }
+void
+waldo (int alignas (int) a,			// { dg-warning "attribute ignored" }
+       int alignas (int),			// { dg-warning "attribute ignored" }
+       int alignas (int) c = 0,			// { dg-warning "attribute ignored" }
+       int alignas (int) = 0)			// { dg-warning "attribute ignored" }
+{
+}
+int plugh (int a alignas (int),			// { dg-error "alignment may not be specified for 'a'" }
+	    int b alignas (int) = 0);		// { dg-error "alignment may not be specified for 'b'" }
+void
+thud (int a alignas (int),			// { dg-error "alignment may not be specified for 'a'" }
+      int b alignas (int) = 0)			// { dg-error "alignment may not be specified for 'b'" }
+{
+}
+enum alignas (int) D { D0 };			// { dg-error "'alignas' on enumerated type" }
+enum class alignas (int) E { E0 };		// { dg-error "'alignas' on enumerated type" }
+enum F {};
+enum alignas (int) F;				// { dg-warning "type attributes ignored after type is already defined" }
+enum G {
+  G0 alignas (int),				// { dg-error "alignment may not be specified for 'G0'" }
+  G1 alignas (int) = 2				// { dg-error "alignment may not be specified for 'G1'" }
+};
+namespace alignas (int) H { using H0 = int; }	// { dg-error "expected identifier before 'alignas'" }
+						// { dg-error "H' does not name a type" "" { target *-*-* } .-1 }
+namespace alignas (int) {}			// { dg-error "expected identifier before 'alignas'" }
+						// { dg-error "expected unqualified-id before '\\\{' token" "" { target *-*-* } .-1 }
+alignas (int) using namespace H;
+						// { dg-error "'H' is not a namespace-name" "" { target *-*-* } .-1 }
+struct alignas (int) I
+{
+  alignas (int);				// { dg-error "declaration does not declare anything" }
+  alignas (int) int i;
+  alignas (int) int foo ();			// { dg-error "'alignas' on function declaration" }
+  alignas (int) int bar () { return 1; }	// { dg-error "'alignas' on function declaration" }
+  alignas (int) int : 0;			// { dg-error "'alignas' on bit-field" }
+  alignas (int) int i2 : 5;			// { dg-error "'alignas' on bit-field" }
+  alignas (int) static int i3;
+  static int i4;
+};
+alignas (int) int I::i4 = 0;
+struct J : alignas (int) C {};			// { dg-warning "attributes on base specifiers are ignored" }
+#if __cpp_concepts >= 201907L
+template <typename T>
+concept K alignas (int) = requires { true; };	// { dg-error "alignment may not be specified for 'K'" "" { target c++20 } }
+#endif
+typedef int L alignas (int);			// { dg-error "'alignas' on a type alias" }
+template <typename T>
+struct M {};
+template <>
+struct alignas (int) M<int> { int m; };
+typedef int N[2] alignas (int);			// { dg-error "'alignas' on a type other than class" }
+typedef int O alignas (int) [2];		// { dg-error "'alignas' on a type alias" }
--- gcc/testsuite/g++.dg/ext/bitfield9.C.jj	2020-01-14 20:02:46.829609145 +0100
+++ gcc/testsuite/g++.dg/ext/bitfield9.C	2024-09-06 20:25:54.024691945 +0200
@@ -3,7 +3,7 @@ 
 
 struct S
 {
-  char a:4;
+  char a:4;			// { dg-warning "alignas' on bit-field" "" { target *-*-* } .+1 }
   char b:8 alignas(int);	// { dg-warning "ISO C\\+\\+ allows bit-field attributes only before the ':' token" }
   char c:8 [[gnu::aligned(8)]];	// { dg-warning "ISO C\\+\\+ allows bit-field attributes only before the ':' token" }
 				// { dg-error "two consecutive '\\\[' shall only introduce an attribute before '\\\[' token" "" { target *-*-* } .-1 }
--- gcc/testsuite/g++.dg/cpp2a/is-layout-compatible3.C.jj	2022-11-17 22:10:05.809657315 +0100
+++ gcc/testsuite/g++.dg/cpp2a/is-layout-compatible3.C	2024-09-06 20:27:54.773223783 +0200
@@ -1,5 +1,6 @@ 
 // P0466R5
 // { dg-do compile { target c++20 } }
+// { dg-options "-pedantic" }
 
 namespace std
 {
@@ -34,7 +35,7 @@  union N { J v; };
 union O { int a; int b; };
 union P { int a : 1; int b : 12; };
 enum Q : int { Q1, Q2 };
-enum alignas(16) R : int { R1, R2 };
+enum alignas(16) R : int { R1, R2 };		// { dg-warning "'alignas' on enumerated type" }
 struct U { [[no_unique_address]] S a1; [[no_unique_address]] S a2; [[no_unique_address]] S a3; };
 struct V { [[no_unique_address]] S b1; [[no_unique_address]] T b2; [[no_unique_address]] S b3; };
 struct alignas(16) A : public I {};