Here since uses_template_parms returns true for all concept-ids, when a
concept-id is used as a default template argument then during deduction
the default argument is considered dependent even after substitution,
which leads to deduction failure (from type_unification_real).
This patch fixes this by implementing the proposed resolution of CWG 2446
which says a concept-id is dependent only if its arguments are.
Bootstrapped and regtestedon x86_64-pc-linux-gnu, does this look OK for
trunk and perhaps 11? Also tested on cmcstl2 and range-v3.
DR 2446
PR c++/102412
gcc/cp/ChangeLog:
* constexpr.c (cxx_eval_constant_expression)
<case TEMPLATE_ID_EXPR>: Check value_dependent_expression_p
instead of processing_template_decl.
* pt.c (value_dependent_expression_p) <case TEMPLATE_ID_EXPR>:
Return true only if any_dependent_template_arguments_p.
(instantiation_dependent_r) <case CALL_EXPR>: Remove this case.
<case TEMPLATE_ID_EXPR>: Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-nondep2.C: New test.
* g++.dg/cpp2a/concepts-nondep3.C: New test.
---
gcc/cp/constexpr.c | 2 +-
gcc/cp/pt.c | 15 ++-----------
gcc/testsuite/g++.dg/cpp2a/concepts-nondep2.C | 21 +++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-nondep3.C | 9 ++++++++
4 files changed, 33 insertions(+), 14 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-nondep2.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-nondep3.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 8a5dd067bcb..18d9d117a48 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -7117,7 +7117,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx,
tree t,
break;
}
- if (!processing_template_decl
+ if (!value_dependent_expression_p (t)
&& !uid_sensitive_constexpr_evaluation_p ())
r = evaluate_concept_check (t);
else
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 22c74da7935..17386286269 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -27191,7 +27191,8 @@ value_dependent_expression_p (tree expression)
}
case TEMPLATE_ID_EXPR:
- return concept_definition_p (TREE_OPERAND (expression, 0));
+ return concept_definition_p (TREE_OPERAND (expression, 0))
+ && any_dependent_template_arguments_p (TREE_OPERAND (expression, 1));
case CONSTRUCTOR:
{
@@ -27598,18 +27599,6 @@ instantiation_dependent_r (tree *tp, int
*walk_subtrees,
case REQUIRES_EXPR:
return *tp;
- case CALL_EXPR:
- /* Treat concept checks as dependent. */
- if (concept_check_p (*tp))
- return *tp;
- break;
-
- case TEMPLATE_ID_EXPR:
- /* Treat concept checks as dependent. */
- if (concept_check_p (*tp))
- return *tp;
- break;
-
case CONSTRUCTOR:
if (CONSTRUCTOR_IS_DEPENDENT (*tp))
return *tp;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-nondep2.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-nondep2.C
new file mode 100644
index 00000000000..e9867f825a1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-nondep2.C
@@ -0,0 +1,21 @@
+// PR c++/102412
+// { dg-do link { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+template<class T, bool = C<int, T>> void f();
+template<> void f<int, true>() { }
+template<> void f<char, false>() { }
+
+template<bool = C<int, char>> void g();
+template<> void g<false>() { }
+
+template<bool = C<int, int>> void h();
+template<> void h<true>() { }
+
+int main() {
+ f<int>();
+ f<char>();
+ g();
+ h();
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-nondep3.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-nondep3.C
new file mode 100644
index 00000000000..ec2d60a43b3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-nondep3.C
@@ -0,0 +1,9 @@
+// DR 2446
+// { dg-do compile { target c++20 } }
+
+template <typename T> concept C = true;
+template <typename T> struct A;
+template <> struct A<bool> { using type = bool; };
+
+template <typename T>
+void f(A<decltype(C<T>)>::type); // OK: no 'typename' needed
--
2.33.0.363.g4c719308ce
