On 9/5/24 9:03 AM, Jakub Jelinek wrote:
Hi!
I've tried to do the same thing I did for normal standard attributes
also for alignas, but there are way too many cases which are silently
accepted although my reading of:
"An alignment-specifier may be applied to a variable or to a class data member,
but it shall not be applied to a bit-field, a function parameter, or an
exception-declaration ([except.handle]).
An alignment-specifier may also be applied to the declaration of a class (in
an elaborated-type-specifier ([dcl.type.elab]) or class-head ([class]),
respectively)."
I've marked the spots where I'd expect some pedwarn with // FIXME.
Clearly we accept it e.g. on bit-fields, exception-declarations, enum
declarations, functions, to e.g. array/reference etc. types, ...
Is some of this intentional?
Allowing it for functions and enums seems consistent with the GNU
aligned attribute, I'd complain only when -pedantic.
I think we might want to pedwarn about standard attribute syntax
appertaining to a type (other than between the class/enum key and name)
when !affects_type_identity. But that seems like a separate issue.
Does GNU aligned on a bit-field do anything useful?
Allowing it on an exception-declaration is a bug, those should be
treated the same as parameters.
Though, trying clang trunk, it diagnoses all the // FIXME lines.
2024-09-05 Jakub Jelinek <ja...@redhat.com>
PR c++/110345
* g++.dg/cpp0x/alignas21.C: New test.
--- gcc/testsuite/g++.dg/cpp0x/alignas21.C.jj 2024-09-05 14:16:44.366395041
+0200
+++ gcc/testsuite/g++.dg/cpp0x/alignas21.C 2024-09-05 14:42:42.690465771
+0200
@@ -0,0 +1,156 @@
+// 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) () {}; // FIXME
+ auto b = [] constexpr alignas (int) {}; // FIXME
+ // { 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) {}; // FIXME
+ // { dg-error "parameter declaration before
lambda exception specification only optional with" "" { target c++20_down } .-1 }
+ auto d = [] () alignas (int) {}; // FIXME
+ 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); // FIXME
+ 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) {} // FIXME
+ try {} catch (alignas (int) int) {} // FIXME
+ 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)) {} // FIXME
+}
+
+alignas (int) int bar (); // FIXME
+using foobar alignas (int) = int; // FIXME
+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);
+int g[2] alignas (int); // FIXME
+int g2 alignas (int) [2];
+int corge () alignas (int); // FIXME
+int *alignas (int) h; // FIXME
+int & alignas (int) i = f; // FIXME
+int && alignas (int) j = 0; // FIXME
+int S::* alignas (int) k; // FIXME
+auto l = sizeof (int [2] alignas (int)); // FIXME
+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 // FIXME
+garply ()
+{
+}
+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 }; // FIXME
+enum class alignas (int) E { E0 }; // FIXME
+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 (); // FIXME
+ alignas (int) int bar () { return 1; } // FIXME
+ alignas (int) int : 0; // FIXME
+ alignas (int) int i2 : 5; // FIXME
+ 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);
+template <typename T>
+struct M {};
+template <>
+struct alignas (int) M<int> { int m; };
+typedef int N[2] alignas (int); // FIXME
+typedef int O alignas (int) [2]; // FIXME
Jakub
