On Thu, Nov 17, 2022 at 07:42:40PM +0100, Jakub Jelinek via Gcc-patches wrote:
> I thought for older C++ this is to catch
> void
> foo ()
> {
> constexpr int a = ({ static constexpr int b = 2; b; });
> }
> and for C++23 the only 3 spots that diagnose those.
> But perhaps for C++20 or older we can check if the var has a context
> of a constexpr function (then assume cp_finish_decl errored or pedwarned
> already) and only error or pedwarn otherwise.
So, here is an updated patch, which in constexpr.cc will accept
DECL_EXPR of decl_*constant_var_p static/thread_local non-extern vars
for C++23 or if they are not declared in constexpr/consteval function.
So, the statement expression case will remain hard error for C++ <= 20 rather
than
pedwarn, because due to the ctx->quiet vs. !ctx->quiet case I don't see
what else we could do, either something is a constant expression, or
it is not, but whether it is or is not shouldn't depend on
-Wpedantic/-Wno-pedantic/-Werror=pedantic.
2022-11-17 Jakub Jelinek <ja...@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_constant_var_p static or thread_local vars for
C++23 and later or if they are declared inside of constexpr or
consteval function.
(potential_constant_expression_1): Similarly, except use
decl_maybe_constant_var_p instead of decl_constant_var_p if
processing_template_decl.
* decl.cc (diagnose_static_in_constexpr): New function.
(start_decl): Remove diagnostics of static or thread_local
vars in constexpr or consteval functions.
(cp_finish_decl): Call diagnose_static_in_constexpr.
gcc/testsuite/
* g++.dg/cpp23/constexpr-nonlit17.C: New test.
* g++.dg/cpp23/constexpr-nonlit18.C: New test.
* g++.dg/cpp23/constexpr-nonlit19.C: New test.
* g++.dg/cpp23/constexpr-nonlit20.C: New test.
* g++.dg/cpp23/feat-cxx2b.C: Adjust expected __cpp_constexpr
value.
* g++.dg/ext/stmtexpr19.C: Don't expect an error for C++20 or later.
--- gcc/c-family/c-cppbuiltin.cc.jj 2022-11-17 09:00:42.106249011 +0100
+++ gcc/c-family/c-cppbuiltin.cc 2022-11-17 09:01:49.286320527 +0100
@@ -1074,7 +1074,7 @@ c_cpp_builtins (cpp_reader *pfile)
/* 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");
--- gcc/cp/constexpr.cc.jj 2022-11-17 08:48:30.530357181 +0100
+++ gcc/cp/constexpr.cc 2022-11-17 20:53:15.432408015 +0100
@@ -7100,17 +7100,35 @@ cxx_eval_constant_expression (const cons
/* Allow __FUNCTION__ etc. */
&& !DECL_ARTIFICIAL (r))
{
- if (!ctx->quiet)
+ bool ok = decl_constant_var_p (r);
+ /* Since P2647R1 control can pass through definitions of static
+ or thread_local vars usable in constant expressions.
+ In C++20 or older, if such vars are declared inside of
+ constexpr or consteval function, diagnose_static_in_constexpr
+ should have already pedwarned on those. Otherwise they could
+ be e.g. in a statement expression, reject those before
+ C++23. */
+ if (ok && cxx_dialect < cxx23)
{
- if (CP_DECL_THREAD_LOCAL_P (r))
- error_at (loc, "control passes through definition of %qD "
- "with thread storage duration", r);
- else
- error_at (loc, "control passes through definition of %qD "
- "with static storage duration", r);
+ tree fnctx = decl_function_context (r);
+ if (fnctx == NULL_TREE
+ || !DECL_DECLARED_CONSTEXPR_P (fnctx))
+ ok = false;
+ }
+ if (!ok)
+ {
+ if (!ctx->quiet)
+ {
+ if (CP_DECL_THREAD_LOCAL_P (r))
+ error_at (loc, "control passes through definition of "
+ "%qD with thread storage duration", r);
+ else
+ error_at (loc, "control passes through definition of "
+ "%qD with static storage duration", r);
+ }
+ *non_constant_p = true;
+ break;
}
- *non_constant_p = true;
- break;
}
if (AGGREGATE_TYPE_P (TREE_TYPE (r))
@@ -9588,21 +9606,41 @@ potential_constant_expression_1 (tree t,
tmp = DECL_EXPR_DECL (t);
if (VAR_P (tmp) && !DECL_ARTIFICIAL (tmp))
{
- if (CP_DECL_THREAD_LOCAL_P (tmp) && !DECL_REALLY_EXTERN (tmp))
- {
- if (flags & tf_error)
- constexpr_error (DECL_SOURCE_LOCATION (tmp), fundef_p,
- "%qD defined %<thread_local%> in "
- "%<constexpr%> context", tmp);
- return false;
- }
- else if (TREE_STATIC (tmp))
+ if (TREE_STATIC (tmp)
+ || (CP_DECL_THREAD_LOCAL_P (tmp) && !DECL_REALLY_EXTERN (tmp)))
{
- if (flags & tf_error)
- constexpr_error (DECL_SOURCE_LOCATION (tmp), fundef_p,
- "%qD defined %<static%> in %<constexpr%> "
- "context", tmp);
- return false;
+ bool ok = (processing_template_decl
+ ? decl_maybe_constant_var_p (tmp)
+ : decl_constant_var_p (tmp));
+ /* Since P2647R1 control can pass through definitions of static
+ or thread_local vars usable in constant expressions.
+ In C++20 or older, if such vars are declared inside of
+ constexpr or consteval function, diagnose_static_in_constexpr
+ should have already pedwarned on those. Otherwise they could
+ be e.g. in a statement expression, reject those before
+ C++23. */
+ if (ok && cxx_dialect < cxx23)
+ {
+ tree fnctx = decl_function_context (tmp);
+ if (fnctx == NULL_TREE
+ || !DECL_DECLARED_CONSTEXPR_P (fnctx))
+ ok = false;
+ }
+ if (!ok)
+ {
+ if (flags & tf_error)
+ {
+ if (CP_DECL_THREAD_LOCAL_P (tmp))
+ constexpr_error (DECL_SOURCE_LOCATION (tmp), fundef_p,
+ "%qD defined %<thread_local%> in "
+ "%<constexpr%> context", tmp);
+ else
+ constexpr_error (DECL_SOURCE_LOCATION (tmp), fundef_p,
+ "%qD defined %<static%> in "
+ "%<constexpr%> context", tmp);
+ }
+ return false;
+ }
}
else if (!check_for_uninitialized_const_var
(tmp, /*constexpr_context_p=*/true, flags))
--- gcc/cp/decl.cc.jj 2022-11-16 14:44:43.692339668 +0100
+++ gcc/cp/decl.cc 2022-11-17 20:53:44.102011594 +0100
@@ -5600,6 +5600,57 @@ groktypename (cp_decl_specifier_seq *typ
return type;
}
+/* For C++17 and older diagnose static or thread_local decls in constexpr
+ or consteval functions. For C++20 similarly, except if they are
+ usable in constant expressions. */
+
+static void
+diagnose_static_in_constexpr (tree decl)
+{
+ if (cxx_dialect >= cxx23)
+ return;
+ if (current_function_decl
+ && VAR_P (decl)
+ && DECL_DECLARED_CONSTEXPR_P (current_function_decl))
+ {
+ bool ok = false;
+ if (processing_template_decl
+ ? decl_maybe_constant_var_p (decl)
+ : decl_constant_var_p (decl))
+ {
+ if (CP_DECL_THREAD_LOCAL_P (decl) && !DECL_REALLY_EXTERN (decl))
+ pedwarn (DECL_SOURCE_LOCATION (decl), OPT_Wpedantic,
+ "%qD defined %<thread_local%> in %qs function only "
+ "available with %<-std=c++2b%> or %<-std=gnu++2b%>", decl,
+ DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
+ ? "consteval" : "constexpr");
+ else if (TREE_STATIC (decl))
+ pedwarn (DECL_SOURCE_LOCATION (decl), OPT_Wpedantic,
+ "%qD defined %<static%> in %qs function only available "
+ "with %<-std=c++2b%> or %<-std=gnu++2b%>", decl,
+ DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
+ ? "consteval" : "constexpr");
+ ok = true;
+ }
+ else if (CP_DECL_THREAD_LOCAL_P (decl) && !DECL_REALLY_EXTERN (decl))
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qD defined %<thread_local%> in %qs function only "
+ "available with %<-std=c++2b%> or %<-std=gnu++2b%>", decl,
+ DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
+ ? "consteval" : "constexpr");
+ else if (TREE_STATIC (decl))
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qD defined %<static%> in %qs function only available "
+ "with %<-std=c++2b%> or %<-std=gnu++2b%>", decl,
+ DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
+ ? "consteval" : "constexpr");
+ else
+ ok = true;
+ if (!ok)
+ cp_function_chain->invalid_constexpr = true;
+ }
+}
+
/* Process a DECLARATOR for a function-scope or namespace-scope
variable or function declaration.
(Function definitions go through start_function; class member
@@ -5860,29 +5911,6 @@ start_decl (const cp_declarator *declara
DECL_THIS_STATIC (decl) = 1;
}
- if (current_function_decl && VAR_P (decl)
- && DECL_DECLARED_CONSTEXPR_P (current_function_decl)
- && cxx_dialect < cxx23)
- {
- bool ok = false;
- if (CP_DECL_THREAD_LOCAL_P (decl) && !DECL_REALLY_EXTERN (decl))
- error_at (DECL_SOURCE_LOCATION (decl),
- "%qD defined %<thread_local%> in %qs function only "
- "available with %<-std=c++2b%> or %<-std=gnu++2b%>", decl,
- DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
- ? "consteval" : "constexpr");
- else if (TREE_STATIC (decl))
- error_at (DECL_SOURCE_LOCATION (decl),
- "%qD defined %<static%> in %qs function only available "
- "with %<-std=c++2b%> or %<-std=gnu++2b%>", decl,
- DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
- ? "consteval" : "constexpr");
- else
- ok = true;
- if (!ok)
- cp_function_chain->invalid_constexpr = true;
- }
-
if (!processing_template_decl && VAR_P (decl))
start_decl_1 (decl, initialized);
@@ -8424,6 +8452,9 @@ cp_finish_decl (tree decl, tree init, bo
set_user_assembler_name (decl, asmspec);
DECL_HARD_REGISTER (decl) = 1;
}
+
+ diagnose_static_in_constexpr (decl);
+
return;
}
@@ -8749,6 +8780,8 @@ cp_finish_decl (tree decl, tree init, bo
&& !DECL_HARD_REGISTER (decl))
targetm.lower_local_decl_alignment (decl);
+ diagnose_static_in_constexpr (decl);
+
invoke_plugin_callbacks (PLUGIN_FINISH_DECL, decl);
}
--- gcc/testsuite/g++.dg/cpp23/constexpr-nonlit17.C.jj 2022-11-17
09:00:42.108248984 +0100
+++ gcc/testsuite/g++.dg/cpp23/constexpr-nonlit17.C 2022-11-17
20:55:33.550498209 +0100
@@ -0,0 +1,12 @@
+// 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 () == ' ');
--- gcc/testsuite/g++.dg/cpp23/constexpr-nonlit18.C.jj 2022-11-17
09:29:45.776136195 +0100
+++ gcc/testsuite/g++.dg/cpp23/constexpr-nonlit18.C 2022-11-17
21:02:20.852865509 +0100
@@ -0,0 +1,49 @@
+// 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 ();
--- gcc/testsuite/g++.dg/cpp23/constexpr-nonlit19.C.jj 2022-11-17
20:56:07.887023431 +0100
+++ gcc/testsuite/g++.dg/cpp23/constexpr-nonlit19.C 2022-11-17
21:04:12.618319027 +0100
@@ -0,0 +1,50 @@
+// P2647R1 - Permitting static constexpr variables in constexpr functions
+// { dg-do compile { target c++14 } }
+// { dg-options "-pedantic" }
+
+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-warning "'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-warning "'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-warning "'a' defined 'static'
in 'constexpr' function only available with" "" { target c++20_down } }
+ return 0;
+}
+
+constexpr int a6 = f6 ();
--- gcc/testsuite/g++.dg/cpp23/constexpr-nonlit20.C.jj 2022-11-17
20:56:28.527738024 +0100
+++ gcc/testsuite/g++.dg/cpp23/constexpr-nonlit20.C 2022-11-17
21:31:25.209729268 +0100
@@ -0,0 +1,50 @@
+// P2647R1 - Permitting static constexpr variables in constexpr functions
+// { dg-do compile { target c++14 } }
+// { dg-options "-Wno-pedantic" }
+
+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;
+ 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);
+ return 0;
+}
+
+constexpr int
+f6 ()
+{
+ static const int a = f1 (0);
+ return 0;
+}
+
+constexpr int a6 = f6 ();
--- gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C.jj 2022-11-17 08:48:30.561356753
+0100
+++ gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C 2022-11-17 09:00:42.108248984
+0100
@@ -134,8 +134,8 @@
#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
--- gcc/testsuite/g++.dg/ext/stmtexpr19.C.jj 2022-11-17 08:48:02.730741221
+0100
+++ gcc/testsuite/g++.dg/ext/stmtexpr19.C 2022-11-17 20:57:06.936206927
+0100
@@ -8,7 +8,7 @@ const test* setup()
{
static constexpr test atest =
{
- ({ static const int inner = 123; &inner; }) // { dg-error "static" }
+ ({ static const int inner = 123; &inner; }) // { dg-error "static" "" {
target c++20_down } }
};
return &atest;
Jakub
