On 6/23/21 2:18 PM, Patrick Palka wrote:
We set DECL_CONTEXT on implicitly generated deduction guides so that their access is consistent with that of the constructor. But this apparently leads to excessive instantiation in some cases, ultimately because instantiation of a deduction guide should be independent of instantiation of the resulting class specialization, but setting the DECL_CONTEXT of the former to the latter breaks this independence.To fix this, this patch makes push_access_scope handle artificial deduction guides specifically instead of setting their DECL_CONTEXT in build_deduction_guide. We could alternatively make the class befriend the guide via DECL_BEFRIENDING_CLASSES, but that'd break class-deduction-access3.C below since friendship isn't transitive. Bootstrapped and regtested on x86_64-pc-linxu-gnu, does this look OK for trunk? PR c++/101174 gcc/cp/ChangeLog: * pt.c (push_access_scope): For artificial deduction guides, set the access scope to that of the constructor. (pop_access_scope): Likewise. (build_deduction_guide): Don't set DECL_CONTEXT. libstdc++-v3/ChangeLog: * testsuite/23_containers/multiset/cons/deduction.cc: Uncomment CTAD example that was rejected by this bug. * testsuite/23_containers/set/cons/deduction.cc: Likewise. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction-access3.C: New test. * g++.dg/cpp1z/class-deduction91.C: New test. --- gcc/cp/pt.c | 11 ++++++---- .../g++.dg/cpp1z/class-deduction-access3.C | 22 +++++++++++++++++++ .../g++.dg/cpp1z/class-deduction91.C | 16 ++++++++++++++ .../23_containers/multiset/cons/deduction.cc | 2 -- .../23_containers/set/cons/deduction.cc | 2 -- 5 files changed, 45 insertions(+), 8 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction-access3.C create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction91.C diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 732fb405adf..5c55507203a 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -236,6 +236,10 @@ push_access_scope (tree t) push_nested_class (DECL_FRIEND_CONTEXT (t)); else if (DECL_CLASS_SCOPE_P (t)) push_nested_class (DECL_CONTEXT (t)); + else if (deduction_guide_p (t) && DECL_ARTIFICIAL (t)) + /* An artificial deduction guide should have the same access as + the constructor. */ + push_nested_class (TREE_TYPE (TREE_TYPE (t)));
Let's be more specific and actually push into the access scope of the constructor (DECL_ABSTRACT_ORIGIN) if set.
else push_to_top_level ();@@ -255,7 +259,9 @@ pop_access_scope (tree t)if (TREE_CODE (t) == FUNCTION_DECL) current_function_decl = saved_access_scope->pop();- if (DECL_FRIEND_CONTEXT (t) || DECL_CLASS_SCOPE_P (t))+ if (DECL_FRIEND_CONTEXT (t) + || DECL_CLASS_SCOPE_P (t) + || (deduction_guide_p (t) && DECL_ARTIFICIAL (t))) pop_nested_class (); else pop_from_top_level (); @@ -28804,9 +28810,6 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com DECL_ABSTRACT_ORIGIN (ded_tmpl) = fn_tmpl; if (ci) set_constraints (ded_tmpl, ci); - /* The artificial deduction guide should have same access as the - constructor. */ - DECL_CONTEXT (ded_fn) = type;return ded_tmpl;} diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction-access3.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction-access3.C new file mode 100644 index 00000000000..44b4b5c455f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction-access3.C @@ -0,0 +1,22 @@ +// { dg-do compile { target c++17 } } + +template<typename T> +struct Cont; + +template<typename T> +struct Base +{ +private: + using type = T; + friend Cont<T>; +}; + +template<typename T> +struct Cont +{ + using argument_type = typename Base<T>::type; + + Cont(T, argument_type) { } +}; + +Cont c(1, 1); diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction91.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction91.C new file mode 100644 index 00000000000..f474c8e35ec --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction91.C @@ -0,0 +1,16 @@ +// PR c++/101174 +// { dg-do compile { target c++17 } } + +struct S { using type = int; }; + +template<class T = int, class U = S> +struct multiset { + using type = typename U::type; + multiset(T); + multiset(U); +}; + +template<class T> +multiset(T) -> multiset<T>; + +multiset c(42); diff --git a/libstdc++-v3/testsuite/23_containers/multiset/cons/deduction.cc b/libstdc++-v3/testsuite/23_containers/multiset/cons/deduction.cc index a4ccc6fa467..8b7a16042a4 100644 --- a/libstdc++-v3/testsuite/23_containers/multiset/cons/deduction.cc +++ b/libstdc++-v3/testsuite/23_containers/multiset/cons/deduction.cc @@ -19,11 +19,9 @@ static_assert(std::is_same_v< decltype(std::multiset{{1, 2, 3}, std::less<int>{}, {}}), std::multiset<int>>);-/* FIXME: GCC 12 rejects this due to PR c++/101174static_assert(std::is_same_v< decltype(std::multiset{{1, 2, 3}, std::less<int>{}}), std::multiset<int>>); -*/static_assert(std::is_same_v<decltype(std::multiset{{1, 2, 3}, SimpleAllocator<int>{}}), diff --git a/libstdc++-v3/testsuite/23_containers/set/cons/deduction.cc b/libstdc++-v3/testsuite/23_containers/set/cons/deduction.cc index 0ae4c2a5c5f..14f36b7c05d 100644 --- a/libstdc++-v3/testsuite/23_containers/set/cons/deduction.cc +++ b/libstdc++-v3/testsuite/23_containers/set/cons/deduction.cc @@ -20,12 +20,10 @@ static_assert(std::is_same_v< std::less<int>{}, {}}), std::set<int>>);-/* FIXME: GCC 12 rejects this due to PR c++/101174static_assert(std::is_same_v< decltype(std::set{{1, 2, 3}, std::less<int>{}}), std::set<int>>); -*/static_assert(std::is_same_v<decltype(std::set{{1, 2, 3},
