The following patch implements this paper.
Per further discussions it is implemented for C++23 only, so isn't
treated as a DR, e.g. because the part of the standard the paper is
changing didn't even exist in C++20.
And we gave up on trying to implement it as a pedwarn rather than
error for C++20 and older, because of implicit constexpr lambdas or
-fimplicit-constexpr reasons.
For C++20 and older, the only change is that passing through
definitions of static or thread_local vars usable in constant expressions
is now accepted in statement expressions if they aren't inside of constexpr
or consteval functions.
2022-11-19 Jakub Jelinek <jakub@redhat.com>
gcc/c-family/
* c-cppbuiltin.cc (c_cpp_builtins): Bump __cpp_constexpr
value from 202207L to 202211L.
gcc/cp/
* constexpr.cc (cxx_eval_constant_expression): Implement C++23
P2647R1 - Permitting static constexpr variables in constexpr functions.
Allow DECL_EXPRs of decl_constant_var_p static or thread_local vars.
(potential_constant_expression_1): Similarly, except use
decl_maybe_constant_var_p instead of decl_constant_var_p if
processing_template_decl.
gcc/testsuite/
* g++.dg/cpp23/constexpr-nonlit17.C: New test.
* g++.dg/cpp23/constexpr-nonlit18.C: New test.
* g++.dg/cpp23/feat-cxx2b.C: Adjust expected __cpp_constexpr
value.
* g++.dg/ext/stmtexpr19.C: Don't expect an error.
* g++.dg/ext/stmtexpr25.C: New test.
/* Set feature test macros for C++23. */
cpp_define (pfile, "__cpp_size_t_suffix=202011L");
cpp_define (pfile, "__cpp_if_consteval=202106L");
- cpp_define (pfile, "__cpp_constexpr=202207L");
+ cpp_define (pfile, "__cpp_constexpr=202211L");
cpp_define (pfile, "__cpp_multidimensional_subscript=202211L");
cpp_define (pfile, "__cpp_named_character_escapes=202207L");
cpp_define (pfile, "__cpp_static_call_operator=202207L");
&& (TREE_STATIC (r)
|| (CP_DECL_THREAD_LOCAL_P (r) && !DECL_REALLY_EXTERN (r)))
/* Allow __FUNCTION__ etc. */
- && !DECL_ARTIFICIAL (r))
+ && !DECL_ARTIFICIAL (r)
+ && !decl_constant_var_p (r))
{
if (!ctx->quiet)
{
case DECL_EXPR:
tmp = DECL_EXPR_DECL (t);
- if (VAR_P (tmp) && !DECL_ARTIFICIAL (tmp))
+ if (VAR_P (tmp) && !DECL_ARTIFICIAL (tmp)
+ && (processing_template_decl
+ ? !decl_maybe_constant_var_p (tmp)
+ : !decl_constant_var_p (tmp)))
{
if (CP_DECL_THREAD_LOCAL_P (tmp) && !DECL_REALLY_EXTERN (tmp))
{
--- /dev/null
+// P2647R1 - Permitting static constexpr variables in constexpr functions
+// { dg-do compile { target c++23 } }
+
+constexpr char
+test ()
+{
+ static const int x = 5;
+ static constexpr char c[] = "Hello World";
+ return *(c + x);
+}
+
+static_assert (test () == ' ');
--- /dev/null
+// P2647R1 - Permitting static constexpr variables in constexpr functions
+// { dg-do compile { target c++14 } }
+
+constexpr int
+f1 (int x)
+{
+ if (x)
+ throw 1;
+ return 0;
+}
+
+constexpr int
+f2 ()
+{
+ static const int a = f1 (1); // { dg-error "'a' defined 'static' in 'constexpr' function only available with" "" { target c++20_down } }
+ return 0;
+}
+
+constexpr int
+f3 ()
+{
+ static const int a = 5; // { dg-error "'a' defined 'static' in 'constexpr' function only available with" "" { target c++20_down } }
+ return 0;
+}
+
+constexpr int
+f4 () // { dg-message "declared here" "" { target c++20_down } }
+{ // { dg-message "is not usable as a 'constexpr' function because:" "" { target c++23 } .-1 }
+ static const int a = f1 (1); // { dg-error "'a' defined 'static' in 'constexpr' function only available with" "" { target c++20_down } }
+ return 0; // { dg-error "'a' defined 'static' in 'constexpr' context" "" { target c++23 } .-1 }
+}
+
+constexpr int a4 = f4 (); // { dg-error "called in a constant expression" }
+
+constexpr int
+f5 ()
+{
+ static const int a = f1 (0); // { dg-error "'a' defined 'static' in 'constexpr' function only available with" "" { target c++20_down } }
+ return 0;
+}
+
+constexpr int
+f6 ()
+{
+ static const int a = f1 (0); // { dg-error "'a' defined 'static' in 'constexpr' function only available with" "" { target c++20_down } }
+ return 0;
+}
+
+constexpr int a6 = f6 (); // { dg-error "called in a constant expression" "" { target c++20_down } }
#ifndef __cpp_constexpr
# error "__cpp_constexpr"
-#elif __cpp_constexpr != 202207
-# error "__cpp_constexpr != 202207"
+#elif __cpp_constexpr != 202211
+# error "__cpp_constexpr != 202211"
#endif
#ifndef __cpp_decltype_auto
{
static constexpr test atest =
{
- ({ static const int inner = 123; &inner; }) // { dg-error "static" }
+ ({ static const int inner = 123; &inner; })
};
return &atest;
--- /dev/null
+// PR c++/81073
+// { dg-options "" }
+// { dg-do compile { target c++11 } }
+
+struct test { const int *addr; };
+
+const test* setup()
+{
+ static constexpr test atest =
+ {
+ ({ static const int inner = (throw 1, 1); &inner; }) // { dg-error "static" "" }
+ };
+
+ return &atest;
+}
+
+int main(){}