On 11/17/22 04:13, Jakub Jelinek wrote:
On Wed, Nov 16, 2022 at 03:26:32PM -0500, Jason Merrill wrote:
On 11/16/22 09:46, Jakub Jelinek wrote:
On Wed, Nov 16, 2022 at 09:33:27AM -0500, Jason Merrill wrote:
and at that point I fear decl_maybe_constant_var_p will not work
properly. Shall this hunk be moved somewhere else (cp_finish_decl?)
where we can already call it, or do the above in start_decl for
cxx_dialect < cxx20 and add a cxx_dialect == cxx20 hunk in cp_finish_decl?
Hmm, I'd expect decl_maybe_constant_var_p to work fine at this point.
For static constexpr vars sure, but what about
static const where start_decl doesn't know the initializer?
Sure, decl_maybe_constant_var_p will not crash in that case, but
it will return true even if the static const var doesn't have
a constant initializer. Sure, we'd catch that later on when actually
trying to constexpr evaluate the function and hitting there the
spots added for C++23 in potential_constant_expression*/cxx_eval_*,
but it would mean that we don't reject it when nothing calls the functions.
I meant something like:
constexpr int bar (int x) { if (x) throw 1; return 0; }
constexpr int foo () { static const int a = bar (1); return 0; }
with -std=c++20 IMHO shouldn't be accepted, while in C++23 it should.
I'd expect us to reject that in C++20 in potential_constant_expression, but
it's a fair point; it is awkward that P2242 wasn't also accepted as a DR.
I pointed out that inconsistency on the reflectors, and it seems that
EWG didn't actually intend P2647 to be a DR, either; it was a CWG error
to propose it as such. But let's go ahead and build on the work you've
done.
Moving the check from start_decl to cp_finish_decl makes sense to me.
So like this? I had to outline the check from start_decl to a function
because it is needed in cp_finish_decl in two different places (the
processing_template_decl path and at the end and it can't be done before the
processing_template_decl spot, because the initializer isn't finalized at
that point for !procesing_template_decl). Also, decl_maybe_constant_var_p
doesn't do what is needed when !processing_template_decl, but I think
we want decl_maybe_constant_var_p in templates so that we don't instantiate
anything.
Lightly tested so far, ok for trunk if it passes full bootstrap/regtest?
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++20 and later.
(potential_constant_expression_1): For C++20 or later, allow
static or thread_local decl_maybe_constant_var_p vars, for
!processing_template_decl only decl_constant_var_p vars.
* decl.cc (diagnose_static_in_constexpr): New function.
(start_decl): Use it for C++17 or earlier.
(cp_finish_decl): Call it for C++20.
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 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 09:56:50.479522863 +0100
@@ -7098,7 +7098,8 @@ cxx_eval_constant_expression (const cons
&& (TREE_STATIC (r)
|| (CP_DECL_THREAD_LOCAL_P (r) && !DECL_REALLY_EXTERN (r)))
/* Allow __FUNCTION__ etc. */
- && !DECL_ARTIFICIAL (r))
+ && !DECL_ARTIFICIAL (r)
+ && (cxx_dialect < cxx20 || !decl_constant_var_p (r)))
I don't think we need to check cxx_dialect here since
diagnose_static_in_constexpr will have already complained.
{
if (!ctx->quiet)
{
@@ -9588,7 +9589,12 @@ 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 (CP_DECL_THREAD_LOCAL_P (tmp)
+ && !DECL_REALLY_EXTERN (tmp)
+ && (cxx_dialect < cxx20
+ || (processing_template_decl
+ ? !decl_maybe_constant_var_p (tmp)
+ : !decl_constant_var_p (tmp))))
Or here.
{
if (flags & tf_error)
constexpr_error (DECL_SOURCE_LOCATION (tmp), fundef_p,
@@ -9596,7 +9602,11 @@ potential_constant_expression_1 (tree t,
"%<constexpr%> context", tmp);
return false;
}
- else if (TREE_STATIC (tmp))
+ else if (TREE_STATIC (tmp)
+ && (cxx_dialect < cxx20
+ || (processing_template_decl
+ ? !decl_maybe_constant_var_p (tmp)
+ : !decl_constant_var_p (tmp))))
{
if (flags & tf_error)
constexpr_error (DECL_SOURCE_LOCATION (tmp), fundef_p,
--- gcc/cp/decl.cc.jj 2022-11-16 14:44:43.692339668 +0100
+++ gcc/cp/decl.cc 2022-11-17 09:54:30.556482833 +0100
@@ -5600,6 +5600,41 @@ 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 (current_function_decl && VAR_P (decl)
+ && DECL_DECLARED_CONSTEXPR_P (current_function_decl)
+ && cxx_dialect < cxx23
+ && (cxx_dialect < cxx20
+ || (processing_template_decl
+ ? !decl_maybe_constant_var_p (decl)
+ : !decl_constant_var_p (decl))))
For (maybe) constant variables let's make this error a pedwarn in C++20
and below.
+ {
+ 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;
+ }
+}
+
/* Process a DECLARATOR for a function-scope or namespace-scope
variable or function declaration.
(Function definitions go through start_function; class member
@@ -5860,28 +5895,8 @@ 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 (cxx_dialect < cxx20)
+ diagnose_static_in_constexpr (decl);
Can we drop this call (and make the ones in cp_finish_decl unconditional)?
if (!processing_template_decl && VAR_P (decl))
start_decl_1 (decl, initialized);
@@ -8424,6 +8439,10 @@ cp_finish_decl (tree decl, tree init, bo
set_user_assembler_name (decl, asmspec);
DECL_HARD_REGISTER (decl) = 1;
}
+
+ if (cxx_dialect == cxx20)
+ diagnose_static_in_constexpr (decl);
+
return;
}
@@ -8749,6 +8768,9 @@ cp_finish_decl (tree decl, tree init, bo
&& !DECL_HARD_REGISTER (decl))
targetm.lower_local_decl_alignment (decl);
+ if (cxx_dialect == cxx20)
+ 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
09:00:42.108248984 +0100
@@ -0,0 +1,12 @@
+// P2647R1 - Permitting static constexpr variables in constexpr functions
+// { dg-do compile { target c++20 } }
+
+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
10:04:32.894045579 +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++17_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++17_down } }
+ return 0;
+}
+
+constexpr int
+f6 () // { dg-message "declared here" "" {
target c++17_down } }
+{
+ static const int a = f1 (0); // { dg-error "'a' defined 'static' in 'constexpr'
function only available with" "" { target c++17_down } }
+ return 0;
+}
+
+constexpr int a6 = f6 (); // { dg-error "called in a constant expression"
"" { target c++17_down } }
--- 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 09:00:42.109248970
+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++17_down } }
};
return &atest;
Jakub
