On Sat, Jan 24, 2026 at 04:14:52PM +0800, Jason Merrill wrote: > On 1/24/26 3:03 PM, Nathaniel Shead wrote: > > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk? > > > > -- >8 -- > > > > What happens in the linked PR is that when evaluating the concept we > > call 'push_to_top_level', we see cfun is non-null, and so call > > 'push_function_context' which sets cfun to NULL and sets a flag so that > > we remember to pop it later. > > > > Then, when instantiating Foo's default constructor as part of the > > concept, we call 'maybe_push_to_top_level'. Here we see that 'Foo' is > > function-local, so '!push_to_top', and we call 'push_function_context'. > > This allocates a new cfun for some reason, and pushes that empty cfun. > > Perhaps maybe_push_to_top_level should check cfun instead of > current_function_decl when setting push_to_top? >
This doesn't seem to work for e.g. g++.dg/cpp0x/noexcept86.C: in maybe_instantiate_noexcept we call maybe_push_to_top_level, and at this point 'cfun' is null, so we call 'push_to_top_level'; this clears the scope_chain and we end up with 'local_specializations == nullptr', and so crash in 'register_local_specializations'. > > Eventually we 'maybe_pop_from_top_level', and restore that newly > > allocated cfun (instead of a NULL cfun), which means that when we start > > trying to build the new-expression (which requires building a statement > > list) we try accessing the (uninitialized) cfun's x_stmt_tree rather > > than the scope_chain's x_stmt_tree, and so crash. > > > > This fixes the issue by also remembering whether we had a cfun when > > doing maybe_push_to_top_level so that we only do push_function_context > > if needed. > > > > PR c++/123663 > > > > gcc/cp/ChangeLog: > > > > * name-lookup.cc (struct local_state_t): New flag has_cfun. > > (local_state_t::save_and_clear): Set has_cfun, call > > push_function_context iff there's a cfun to save. > > (local_state_t::restore): call pop_function_context if > > has_cfun is set. > > (maybe_push_to_top_level): Delegte push_function_context to > > local_state_t::save_and_clear. > > (maybe_pop_from_top_level): Delegate pop_function_context to > > local_state_t::restore. > > > > gcc/testsuite/ChangeLog: > > > > * g++.dg/cpp2a/concepts-pr123663.C: New test. > > > > Signed-off-by: Nathaniel Shead <[email protected]> > > --- > > gcc/cp/name-lookup.cc | 12 +++++++----- > > gcc/testsuite/g++.dg/cpp2a/concepts-pr123663.C | 13 +++++++++++++ > > 2 files changed, 20 insertions(+), 5 deletions(-) > > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-pr123663.C > > > > diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc > > index 1b3713dc40e..10c45548dc2 100644 > > --- a/gcc/cp/name-lookup.cc > > +++ b/gcc/cp/name-lookup.cc > > @@ -8957,6 +8957,7 @@ struct local_state_t > > int cp_unevaluated_operand; > > int c_inhibit_evaluation_warnings; > > int cp_noexcept_operand_; > > + bool has_cfun; > > static local_state_t > > save_and_clear () > > @@ -8968,6 +8969,9 @@ struct local_state_t > > ::c_inhibit_evaluation_warnings = 0; > > s.cp_noexcept_operand_ = ::cp_noexcept_operand; > > ::cp_noexcept_operand = 0; > > + s.has_cfun = !!cfun; > > + if (s.has_cfun) > > + push_function_context (); > > return s; > > } > > @@ -8977,6 +8981,8 @@ struct local_state_t > > ::cp_unevaluated_operand = this->cp_unevaluated_operand; > > ::c_inhibit_evaluation_warnings = this->c_inhibit_evaluation_warnings; > > ::cp_noexcept_operand = this->cp_noexcept_operand_; > > + if (this->has_cfun) > > + pop_function_context (); > > } > > }; > > @@ -9005,7 +9011,6 @@ maybe_push_to_top_level (tree d) > > else > > { > > gcc_assert (!processing_template_decl); > > - push_function_context (); > > local_state_stack.safe_push (local_state_t::save_and_clear ()); > > } > > @@ -9020,10 +9025,7 @@ maybe_pop_from_top_level (bool push_to_top) > > if (push_to_top) > > pop_from_top_level (); > > else > > - { > > - local_state_stack.pop ().restore (); > > - pop_function_context (); > > - } > > + local_state_stack.pop ().restore (); > > } > > /* Push into the scope of the namespace NS, even if it is deeply > > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr123663.C > > b/gcc/testsuite/g++.dg/cpp2a/concepts-pr123663.C > > new file mode 100644 > > index 00000000000..8ac303683c0 > > --- /dev/null > > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr123663.C > > @@ -0,0 +1,13 @@ > > +// PR c++/123663 > > +// { dg-do compile { target c++20 } } > > + > > +template <typename T> > > +concept TestConcept = requires { > > + new T[1]{}; > > +}; > > +struct base { > > + base() { > > + struct Foo {}; > > + TestConcept<Foo>; > > + } > > +}; >
