--- gcc/testsuite/g++.dg/cpp0x/attr-fallthrough1.C.jj	2024-09-04 16:27:52.786654084 +0200
+++ gcc/testsuite/g++.dg/cpp0x/attr-fallthrough1.C	2024-09-04 16:44:41.879666097 +0200
@@ -0,0 +1,169 @@
+// 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)
+{
+  switch (n)
+    {
+    case 1:
+      [[fallthrough (n > 0)]];			// { dg-error "'fallthrough' attribute does not take any arguments" }
+    case 2:
+      break;
+    case 3:
+      [[fallthrough]];
+    case 4:
+      break;
+    case 5:
+      [[fallthrough ("abc")]];			// { dg-error "'fallthrough' attribute does not take any arguments" }
+    case 6:
+      break;
+    case 7:
+      [[fallthrough (1, 2, 3)]];		// { dg-error "'fallthrough' attribute does not take any arguments" }
+    case 8:
+      [[fallthrough]];				// { dg-error "attribute 'fallthrough' not preceding a case label or default label" }
+      foo (n - 1);
+      break;
+    default:
+      break;
+    }
+
+  [[fallthrough]] int x1;			// { dg-error "'fallthrough' attribute ignored" }
+
+  auto a = [] [[fallthrough]] () {};		// { dg-error "'fallthrough' attribute ignored" }
+  auto b = [] constexpr [[fallthrough]] {};	// { dg-error "'fallthrough' attribute ignored" }
+						// { 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 [[fallthrough]] {};	// { dg-error "'fallthrough' attribute ignored" }
+						// { dg-error "parameter declaration before lambda exception specification only optional with" "" { target c++20_down } .-1 }
+  auto d = [] () [[fallthrough]] {};		// { dg-error "'fallthrough' attribute ignored" }
+  auto e = new int [n] [[fallthrough]];		// { dg-warning "attributes ignored on outermost array type in new expression" }
+  auto e2 = new int [n] [[fallthrough]] [42];	// { dg-warning "attributes ignored on outermost array type in new expression" }
+  auto f = new int [n][42] [[fallthrough]];	// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] {}				// { dg-warning "attributes at the beginning of statement are ignored" }
+  [[fallthrough]] if (true) {}			// { dg-warning "attributes at the beginning of statement are ignored" }
+  [[fallthrough]] while (false) {}		// { dg-warning "attributes at the beginning of statement are ignored" }
+  [[fallthrough]] goto lab;			// { dg-warning "attributes at the beginning of statement are ignored" }
+  [[fallthrough]] lab:;				// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] try {} catch (int) {}		// { dg-warning "attributes at the beginning of statement are ignored" }
+  if ([[fallthrough]] int x = 0) {}		// { dg-error "'fallthrough' attribute ignored" }
+  switch (n)
+    {
+    [[fallthrough]] case 1:			// { dg-error "'fallthrough' attribute ignored" }
+    [[fallthrough]] break;			// { dg-warning "attributes at the beginning of statement are ignored" }
+    [[fallthrough]] default:			// { dg-error "'fallthrough' attribute ignored" }
+	 break;
+    }
+  for ([[fallthrough]] auto a : arr) {}		// { dg-error "'fallthrough' attribute ignored" }
+  for ([[fallthrough]] auto [a, b] : arr2) {}	// { dg-error "'fallthrough' attribute ignored" }
+						// { dg-error "structured bindings only available with" "" { target c++14_down } .-1 }
+  [[fallthrough]] asm ("");			// { dg-warning "attributes ignored on 'asm' declaration" }
+  try {} catch ([[fallthrough]] int x) {}	// { dg-error "'fallthrough' attribute ignored" }
+  try {} catch ([[fallthrough]] int) {}		// { dg-error "'fallthrough' attribute ignored" }
+  try {} catch (int [[fallthrough]] x) {}	// { dg-warning "attribute ignored" }
+  try {} catch (int [[fallthrough]]) {}		// { dg-warning "attribute ignored" }
+  try {} catch (int x [[fallthrough]]) {}	// { dg-error "'fallthrough' attribute ignored" }
+}
+
+[[fallthrough]] int bar ();			// { dg-error "'fallthrough' attribute ignored" }
+using foobar [[fallthrough]] = int;		// { dg-error "'fallthrough' attribute ignored" }
+[[fallthrough]] int a;				// { dg-error "'fallthrough' attribute ignored" }
+[[fallthrough]] auto [b, c] = arr;		// { dg-error "'fallthrough' attribute ignored" }
+						// { dg-error "structured bindings only available with" "" { target c++14_down } .-1 }
+[[fallthrough]];				// { dg-warning "attribute ignored" }
+inline [[fallthrough]] void baz () {}		// { dg-warning "attribute ignored" }
+						// { dg-error "standard attributes in middle of decl-specifiers" "" { target *-*-* } .-1 }
+constexpr [[fallthrough]] int qux () { return 0; }	// { dg-warning "attribute ignored" }
+						// { dg-error "standard attributes in middle of decl-specifiers" "" { target *-*-* } .-1 }
+int [[fallthrough]] d;				// { dg-warning "attribute ignored" }
+int const [[fallthrough]] e = 1;		// { dg-warning "attribute ignored" }
+struct A {} [[fallthrough]];			// { dg-warning "attribute ignored in declaration of 'struct A'" }
+struct A [[fallthrough]];			// { dg-warning "attribute ignored" }
+struct A [[fallthrough]] a1;			// { dg-warning "attribute ignored" }
+A [[fallthrough]] a2;				// { dg-warning "attribute ignored" }
+enum B { B0 } [[fallthrough]];			// { dg-warning "attribute ignored in declaration of 'enum B'" }
+enum B [[fallthrough]];				// { dg-warning "attribute ignored" }
+enum B [[fallthrough]] b1;			// { dg-warning "attribute ignored" }
+B [[fallthrough]] b2;				// { dg-warning "attribute ignored" }
+struct [[fallthrough]] C {};			// { dg-error "'fallthrough' attribute ignored" }
+int f [[fallthrough]];				// { dg-error "'fallthrough' attribute ignored" }
+int g[2] [[fallthrough]];			// { dg-error "'fallthrough' attribute ignored" }
+int g2 [[fallthrough]] [2];			// { dg-error "'fallthrough' attribute ignored" }
+int corge () [[fallthrough]];			// { dg-error "'fallthrough' attribute ignored" }
+int *[[fallthrough]] h;				// { dg-error "'fallthrough' attribute ignored" }
+int & [[fallthrough]] i = f;			// { dg-error "'fallthrough' attribute ignored" }
+int && [[fallthrough]] j = 0;			// { dg-error "'fallthrough' attribute ignored" }
+int S::* [[fallthrough]] k;			// { dg-error "'fallthrough' attribute ignored" }
+auto l = sizeof (int [2] [[fallthrough]]);	// { dg-error "'fallthrough' attribute ignored" }
+int freddy ([[fallthrough]] int a,		// { dg-error "'fallthrough' attribute ignored" }
+	    [[fallthrough]] int,		// { dg-error "'fallthrough' attribute ignored" }
+	    [[fallthrough]] int c = 0,		// { dg-error "'fallthrough' attribute ignored" }
+	    [[fallthrough]] int = 0);		// { dg-error "'fallthrough' attribute ignored" }
+void
+corge ([[fallthrough]] int a,			// { dg-error "'fallthrough' attribute ignored" }
+       [[fallthrough]] int,			// { dg-error "'fallthrough' attribute ignored" }
+       [[fallthrough]] int c = 0,		// { dg-error "'fallthrough' attribute ignored" }
+       [[fallthrough]] int = 0)			// { dg-error "'fallthrough' attribute ignored" }
+{
+}
+[[fallthrough]] void
+garply ()					// { dg-error "'fallthrough' attribute ignored" }
+{
+}
+int grault (int [[fallthrough]] a,		// { dg-warning "attribute ignored" }
+	    int [[fallthrough]],		// { dg-warning "attribute ignored" }
+	    int [[fallthrough]] c = 0,		// { dg-warning "attribute ignored" }
+	    int [[fallthrough]] = 0);		// { dg-warning "attribute ignored" }
+void
+waldo (int [[fallthrough]] a,			// { dg-warning "attribute ignored" }
+       int [[fallthrough]],			// { dg-warning "attribute ignored" }
+       int [[fallthrough]] c = 0,		// { dg-warning "attribute ignored" }
+       int [[fallthrough]] = 0)			// { dg-warning "attribute ignored" }
+{
+}
+int plugh (int a [[fallthrough]],		// { dg-error "'fallthrough' attribute ignored" }
+	    int b [[fallthrough]] = 0);		// { dg-error "'fallthrough' attribute ignored" }
+void
+thud (int a [[fallthrough]],			// { dg-error "'fallthrough' attribute ignored" }
+      int b [[fallthrough]] = 0)		// { dg-error "'fallthrough' attribute ignored" }
+{
+}
+enum [[fallthrough]] D { D0 };			// { dg-error "'fallthrough' attribute ignored" }
+enum class [[fallthrough]] E { E0 };		// { dg-error "'fallthrough' attribute ignored" }
+enum F {};
+enum [[fallthrough]] F;				// { dg-warning "type attributes ignored after type is already defined" }
+enum G {
+  G0 [[fallthrough]],				// { dg-error "'fallthrough' attribute ignored" }
+  G1 [[fallthrough]] = 2			// { dg-error "'fallthrough' attribute ignored" }
+};
+namespace [[fallthrough]] H { using H0 = int; }	// { dg-warning "'fallthrough' attribute directive ignored" } */
+namespace [[fallthrough]] {}			// { dg-warning "'fallthrough' attribute directive ignored" }
+[[fallthrough]] using namespace H;		// { dg-warning "'fallthrough' attribute directive ignored" }
+struct [[fallthrough]] I			// { dg-error "'fallthrough' attribute ignored" }
+{
+  [[fallthrough]];				// { dg-error "declaration does not declare anything" }
+  [[fallthrough]] int i;			// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] int foo ();			// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] int bar () { return 1; }	// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] int : 0;			// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] int i2 : 5;			// { dg-error "'fallthrough' attribute ignored" }
+  [[fallthrough]] static int i3;		// { dg-error "'fallthrough' attribute ignored" }
+  static int i4;
+};
+[[fallthrough]] int I::i4 = 0;			// { dg-error "'fallthrough' attribute ignored" }
+struct J : [[fallthrough]] C {};		// { dg-warning "attributes on base specifiers are ignored" }
+#if __cpp_concepts >= 201907L
+template <typename T>
+concept K [[fallthrough]] = requires { true; };	// { dg-error "'fallthrough' attribute ignored" "" { target c++20 } }
+#endif
+typedef int L [[fallthrough]];			// { dg-error "'fallthrough' attribute ignored" }
+template <typename T>
+struct M {};
+template <>
+struct [[fallthrough]] M<int> { int m; };	// { dg-error "'fallthrough' attribute ignored" }
+typedef int N[2] [[fallthrough]];		// { dg-error "'fallthrough' attribute ignored" }
+typedef int O [[fallthrough]] [2];		// { dg-error "'fallthrough' attribute ignored" }
--- gcc/testsuite/g++.dg/cpp0x/attr-fallthrough2.C.jj	2024-09-04 16:46:49.540022110 +0200
+++ gcc/testsuite/g++.dg/cpp0x/attr-fallthrough2.C	2024-09-04 16:46:45.707071471 +0200
@@ -0,0 +1,10 @@
+// C++ 26 P2552R3 - On the ignorability of standard attributes
+// { dg-do compile { target c++11 } }
+
+void
+foo ()
+{
+  [[fallthrough]];			// { dg-error "invalid use of attribute 'fallthrough'" }
+lab:;
+  goto lab;
+}
