From 01aff2ba18a654324957af446a3065db489c0f14 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Thu, 23 Jun 2022 16:18:55 -0400 Subject: [PATCH] c++: context completion in lookup_template_class [PR105982] The below testcase demonstrates that completion of the substituted context during lookup_template_class can end up registering the desired specialization for us in more cases than r13-1045-gcb7fd1ea85feea anticipated. In particular this can happen for a non-dependent specialization of a nested class as well. For this testcase, during overload resolution with A's guides, we substitute the deduced argument T=int into the TYPENAME_TYPE B::C, during which we call lookup_template_class for A::B with T=int, which completes A for the first time, which recursively registers the desired specialization of B already. The parent call to lookup_template_class then tries to register the same specialization, triggering an ICE. This patch fixes this by making lookup_template_class determine more directly whether we need to recheck the specializations table after completion of the context -- when and only when the call to complete_type had an effect. PR c++/105982 gcc/cp/ChangeLog: * pt.cc (lookup_template_class): After calling complete_type for the substituted context, check the table again iff the type was previously incomplete and complete_type made it complete. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/class-deduction111.C: New test. --- gcc/cp/pt.cc | 21 ++++++++++++--------- gcc/testsuite/g++.dg/cpp1z/class-deduction111.C | 10 ++++++++++ 2 files changed, 22 insertions(+), 9 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction111.C diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 12a2b57..8672da1 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -10089,16 +10089,19 @@ lookup_template_class (tree d1, tree arglist, tree in_decl, tree context, { context = tsubst_aggr_type (context, arglist, complain, in_decl, true); - context = complete_type (context); - if (is_dependent_type && arg_depth > 1) + /* Try completing the enclosing context if it's not already so. */ + if (context != error_mark_node + && !COMPLETE_TYPE_P (context)) { - /* If this is a dependent nested specialization such as - A::B [with T=int, U=U], then completion of A - could have caused to register the desired specialization - of B already, so check the table again (33959). */ - entry = type_specializations->find_with_hash (&elt, hash); - if (entry) - return entry->spec; + context = complete_type (context); + if (COMPLETE_TYPE_P (context)) + { + /* Completion could have caused us to register the desired + specialization already, so check the table again. */ + entry = type_specializations->find_with_hash (&elt, hash); + if (entry) + return entry->spec; + } } } } diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction111.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction111.C new file mode 100644 index 0000000..2406529 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction111.C @@ -0,0 +1,10 @@ +// PR c++/105982 +// { dg-do compile { target c++17 } } + +template +struct A { + struct B { struct C { }; }; + A(T, typename B::C); +}; + +A a(0, {}); -- 2.7.4