https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99009
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:1dabbfb0f4a9fbdc77e1ea4db7302586f00895e1 commit r11-7483-g1dabbfb0f4a9fbdc77e1ea4db7302586f00895e1 Author: Marek Polacek <pola...@redhat.com> Date: Fri Feb 12 12:21:15 2021 -0500 c++: ICE with deduction guide in checking type-dep [PR99009, PR97034] We represent deduction guides with FUNCTION_DECLs, but they are built without DECL_CONTEXT, leading to an ICE in type_dependent_expression_p on the assert that the type of a function template with no dependent (innermost!) template arguments must be non-dependent. Consider the attached class-deduction79.C: we create a deduction guide: template<class T> G(T)-> E<Z>::G<T> we deduce T and create a partial instantiation: G(T) -> E<Z>::G<T> [with T = int] And then do_class_deduction wants to create a CALL_EXPR from the above using build_new_function_call -> build_over_call which calls mark_used -> maybe_instantiate_noexcept -> type_dependent_expression_p. There, the innermost template arguments are non-dependent (<int>), but the fntype is dependent -- the return type is a TYPENAME_TYPE, and since we have no DECL_CONTEXT, this check holds: /* Otherwise, if the function decl isn't from a dependent scope, it can't be type-dependent. Checking this is important for functions with auto return type, which looks like a dependent type. */ if (TREE_CODE (expression) == FUNCTION_DECL && !(DECL_CLASS_SCOPE_P (expression) && dependent_type_p (DECL_CONTEXT (expression))) whereupon we ICE. This patch fixes it by deferring the class deduction until the enclosing scope is non-dependent. build_deduction_guide and maybe_aggr_guide needed a little tweaking to make the deduction work in a member template. Co-Authored-By: Jason Merrill <ja...@redhat.com> gcc/cp/ChangeLog: PR c++/97034 PR c++/99009 * pt.c (build_deduction_guide): Use INNERMOST_TEMPLATE_ARGS. (maybe_aggr_guide): Use the original template type where needed. In a class member template, partially instantiate the result of collect_ctor_idx_types. (do_class_deduction): Defer the deduction until the enclosing scope is non-dependent. gcc/testsuite/ChangeLog: PR c++/97034 PR c++/99009 * g++.dg/cpp1z/class-deduction81.C: New test. * g++.dg/cpp1z/class-deduction82.C: New test. * g++.dg/cpp2a/class-deduction-aggr8.C: New test. * g++.dg/cpp2a/class-deduction-aggr9.C: New test. * g++.dg/cpp2a/class-deduction-aggr10.C: New test.
