c++: Fix behaviour of nested maybe_push_to_top_level [PR123663]

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.

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.

This also seems to fix PR123354.

	PR c++/123663
	PR c++/123354

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.
	* g++.dg/template/pr123354.C

Reviewed-by: Jason Merrill <jason@redhat.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>

diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index a1f0a0ff38e17fae1744ae3af7968a1394879487..a187d65b509ee4d39606ddc441352d03996bce5a 100644 (file)
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -8960,6 +8960,7 @@ 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 ()
@@ -8971,6 +8972,9 @@ 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;
   }
 
@@ -8980,6 +8984,8 @@ 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 ();
   }
 };
 
@@ -9008,7 +9014,6 @@ 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 ());
     }
 
@@ -9023,10 +9028,7 @@ 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 (file)
index 0000000..8ac3036
--- /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>;
+  }
+};

diff --git a/gcc/testsuite/g++.dg/template/pr123354.C b/gcc/testsuite/g++.dg/template/pr123354.C
new file mode 100644 (file)
index 0000000..f87956a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr123354.C
@@ -0,0 +1,18 @@
+// PR c++/123354
+// { dg-do compile { target c++11 } }
+// ICE with static local var referenced in NSDMI of local class
+
+template<typename T>
+void foo() {
+    static constexpr int value = 42;
+    struct s1_t {
+        struct s2_t {
+            int dummy { 0 };
+            char* ptr { static_cast<char*>(::operator new(sizeof(value)))};
+        } s2;
+    } object;
+}
+
+int main() {
+    foo<void>();
+}