On 1/24/26 6:38 PM, Nathaniel Shead wrote:
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'.
Ah, well. The patch is OK.
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>;
+ }
+};
