PR c++/91378 - ICE with noexcept and auto return type.

Here, since the call to g is not type-dependent, we call mark_used on it to
determine its return type.  This also wants to instantiate the
noexcept-expression.  But since nothing in maybe_instantiate_noexcept was
calling push_to_top_level, we substituted b.i with processing_template_decl
set, so we left it unresolved for later access checking.  As a result, the
type of C::g<int> remained instantiation-dependent, leading to an ICE in
type_dependent_expression_p on the assert that the type of a function
template with no dependent template arguments must be non-dependent.

	* pt.c (maybe_instantiate_noexcept): push_to_top_level.

From-SVN: r274143

gcc/cp/ChangeLog

+2019-08-06  Jason Merrill  <jason@redhat.com>
+
+	PR c++/91378 - ICE with noexcept and auto return type.
+	* pt.c (maybe_instantiate_noexcept): push_to_top_level.
+
 2019-08-06  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* decl.c (check_array_designated_initializer): Use

gcc/cp/pt.c

@@ -24315,12 +24315,11 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
 	}
       else if (push_tinst_level (fn))
 	{
+	  push_to_top_level ();
 	  push_access_scope (fn);
 	  push_deferring_access_checks (dk_no_deferred);
 	  input_location = DECL_SOURCE_LOCATION (fn);
 
-	  tree save_ccp = current_class_ptr;
-	  tree save_ccr = current_class_ref;
 	  /* If needed, set current_class_ptr for the benefit of
 	     tsubst_copy/PARM_DECL.  */
 	  tree tdecl = DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (fn));
@@ -24346,9 +24345,6 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
 					/*function_p=*/false,
 					/*i_c_e_p=*/true);
 
-	  current_class_ptr = save_ccp;
-	  current_class_ref = save_ccr;
-
 	  /* Build up the noexcept-specification.  */
 	  spec = build_noexcept_spec (noex, tf_warning_or_error);
 
@@ -24358,6 +24354,7 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
 	  pop_deferring_access_checks ();
 	  pop_access_scope (fn);
 	  pop_tinst_level ();
+	  pop_from_top_level ();
 	}
       else
 	spec = noexcept_false_spec;

gcc/testsuite/g++.dg/cpp1y/auto-fn56.C

+// PR c++/91378
+// { dg-do compile { target c++14 } }
+
+struct B
+{
+  int i;
+};
+
+struct C
+{
+  template <class T> static auto
+  g(B b) noexcept(noexcept(b.i)) { }
+};
+
+template <class T>
+void h(T t)
+{
+  C::g<int>({});
+}