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From: Patrick Palka <ppalka@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-3822] c++: concept-ids and value-dependence [PR102412] Date: Wed, 22 Sep 2021 15:18:10 +0000 (GMT) [thread overview] Message-ID: <20210922151810.3186E385841E@sourceware.org> (raw) https://gcc.gnu.org/g:9329344a6d81a6a5e3bd171167ebc7b158bb44f4 commit r12-3822-g9329344a6d81a6a5e3bd171167ebc7b158bb44f4 Author: Patrick Palka <ppalka@redhat.com> Date: Wed Sep 22 11:16:53 2021 -0400 c++: concept-ids and value-dependence [PR102412] The problem here is that uses_template_parms returns true for all concept-ids (even those with non-dependent arguments), so when a concept-id is used as a default template argument then during deduction the default argument is considered dependent even after substituting into it, which leads to deduction failure (from type_unification_real). This patch fixes this by implementing the resolution of CWG 2446 which says a concept-id is dependent only if its arguments are. 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. Diff: --- 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(-) 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 28ba32f416c..6bd6ceb29be 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -27247,7 +27247,8 @@ 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: { @@ -27654,18 +27655,6 @@ 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..4aae2871d0c --- /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
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