https://gcc.gnu.org/g:5c6364b09a67de8d2237f65016ea1e3365a76e8d
commit r16-968-g5c6364b09a67de8d2237f65016ea1e3365a76e8d
Author: Jason Merrill <ja...@redhat.com>
Date: Thu May 29 12:21:28 2025 -0400
c++: C++17 constexpr lambda and goto/static
We only want the error for these cases for functions explicitly declared
constexpr, but we still want to set invalid_constexpr on C++17 lambdas so
maybe_save_constexpr_fundef doesn't make them implicitly constexpr.
The potential_constant_expression_1 change isn't necessary for this test,
but still seems correct.
gcc/cp/ChangeLog:
* decl.cc (start_decl): Also set invalid_constexpr
for maybe_constexpr_fn.
* parser.cc (cp_parser_jump_statement): Likewise.
* constexpr.cc (potential_constant_expression_1): Ignore
goto to an artificial label.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1z/constexpr-lambda29.C: New test.
Diff:
---
gcc/cp/constexpr.cc | 3 +++
gcc/cp/decl.cc | 28 +++++++++++++++----------
gcc/cp/parser.cc | 7 ++++---
gcc/testsuite/g++.dg/cpp1z/constexpr-lambda29.C | 19 +++++++++++++++++
4 files changed, 43 insertions(+), 14 deletions(-)
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index fa754b9a176a..272fab328968 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -10979,6 +10979,9 @@ potential_constant_expression_1 (tree t, bool
want_rval, bool strict, bool now,
*jump_target = *target;
return true;
}
+ if (DECL_ARTIFICIAL (*target))
+ /* The user didn't write this goto, this isn't the problem. */
+ return true;
if (flags & tf_error)
constexpr_error (loc, fundef_p, "%<goto%> is not a constant "
"expression");
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index a9ef28bfd805..ec4b6298b11a 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -6198,22 +6198,28 @@ start_decl (const cp_declarator *declarator,
}
if (current_function_decl && VAR_P (decl)
- && DECL_DECLARED_CONSTEXPR_P (current_function_decl)
+ && maybe_constexpr_fn (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++23%> or %<-std=gnu++23%>", decl,
- DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
- ? "consteval" : "constexpr");
+ {
+ if (DECL_DECLARED_CONSTEXPR_P (current_function_decl))
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qD defined %<thread_local%> in %qs function only "
+ "available with %<-std=c++23%> or %<-std=gnu++23%>", 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++23%> or %<-std=gnu++23%>", decl,
- DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
- ? "consteval" : "constexpr");
+ {
+ if (DECL_DECLARED_CONSTEXPR_P (current_function_decl))
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "%qD defined %<static%> in %qs function only available "
+ "with %<-std=c++23%> or %<-std=gnu++23%>", decl,
+ DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
+ ? "consteval" : "constexpr");
+ }
else
ok = true;
if (!ok)
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 3e39bf33fab0..091873cbe3a9 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -15431,11 +15431,12 @@ cp_parser_jump_statement (cp_parser* parser, tree
&std_attrs)
case RID_GOTO:
if (parser->in_function_body
- && DECL_DECLARED_CONSTEXPR_P (current_function_decl)
+ && maybe_constexpr_fn (current_function_decl)
&& cxx_dialect < cxx23)
{
- error ("%<goto%> in %<constexpr%> function only available with "
- "%<-std=c++23%> or %<-std=gnu++23%>");
+ if (DECL_DECLARED_CONSTEXPR_P (current_function_decl))
+ error ("%<goto%> in %<constexpr%> function only available with "
+ "%<-std=c++23%> or %<-std=gnu++23%>");
cp_function_chain->invalid_constexpr = true;
}
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda29.C
b/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda29.C
new file mode 100644
index 000000000000..9e661b6a55d4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda29.C
@@ -0,0 +1,19 @@
+// Test that we don't make lambdas with goto/static implicitly constexpr
+// when an explicitly constexpr function would be ill-formed.
+
+// { dg-do compile { target c++17 } }
+
+int main()
+{
+ constexpr int a = [] {
+ return 42;
+ goto label;
+ label:
+ return 142;
+ }(); // { dg-error "" "" { target c++20_down } }
+
+ constexpr int b = [] {
+ return 42;
+ static int i;
+ }(); // { dg-error "" "" { target c++20_down } }
+}
