[gcc r12-7291] c++: implicit 'this' in noexcept-spec within class tmpl [PR94944]

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:36278f48cbc08c78e4ed588e5a049bd45fd1c55a

commit r12-7291-g36278f48cbc08c78e4ed588e5a049bd45fd1c55a
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Feb 17 20:20:24 2022 -0500

    c++: implicit 'this' in noexcept-spec within class tmpl [PR94944]
    
    Here when instantiating the noexcept-spec we fail to resolve the
    implicit object for the member call A<T>::f() ultimately because
    maybe_instantiate_noexcept sets current_class_ptr/ref to the dependent
    'this' (of type B<T>) rather than the specialized 'this' (of type B<int>).
    
    This patch fixes this by making maybe_instantiate_noexcept set
    current_class_ptr/ref to the specialized 'this' instead, consistent
    with what tsubst_function_type does when substituting into the trailing
    return type of a non-static member function.
    
            PR c++/94944
    
    gcc/cp/ChangeLog:
    
            * pt.cc (maybe_instantiate_noexcept): For non-static member
            functions, set current_class_ptr/ref to the specialized 'this'
            instead.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/noexcept34.C: Adjusted expected diagnostics.
            * g++.dg/cpp0x/noexcept75.C: New test.

Diff:
---
 gcc/cp/pt.cc                            | 19 +++++++------------
 gcc/testsuite/g++.dg/cpp0x/noexcept34.C |  8 ++++----
 gcc/testsuite/g++.dg/cpp0x/noexcept75.C | 17 +++++++++++++++++
 3 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 352cff944d0..16bedbc4bc7 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -26140,20 +26140,15 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
 	  push_deferring_access_checks (dk_no_deferred);
 	  input_location = DECL_SOURCE_LOCATION (fn);
 
-	  if (!DECL_LOCAL_DECL_P (fn))
+	  if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fn)
+	      && !DECL_LOCAL_DECL_P (fn))
 	    {
 	      /* If needed, set current_class_ptr for the benefit of
-		 tsubst_copy/PARM_DECL.  The exception pattern will
-		 refer to the parm of the template, not the
-		 instantiation.  */
-	      tree tdecl = DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (fn));
-	      if (DECL_NONSTATIC_MEMBER_FUNCTION_P (tdecl))
-		{
-		  tree this_parm = DECL_ARGUMENTS (tdecl);
-		  current_class_ptr = NULL_TREE;
-		  current_class_ref = cp_build_fold_indirect_ref (this_parm);
-		  current_class_ptr = this_parm;
-		}
+		 tsubst_copy/PARM_DECL.  */
+	      tree this_parm = DECL_ARGUMENTS (fn);
+	      current_class_ptr = NULL_TREE;
+	      current_class_ref = cp_build_fold_indirect_ref (this_parm);
+	      current_class_ptr = this_parm;
 	    }
 
 	  /* If this function is represented by a TEMPLATE_DECL, then
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept34.C b/gcc/testsuite/g++.dg/cpp0x/noexcept34.C
index dce35652ef5..86129e7a520 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept34.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept34.C
@@ -7,13 +7,13 @@ template<typename> struct A
 {
   constexpr int f () { return 0; }
   bool b = true;
-  void g () noexcept (f()) { } // { dg-error "use of parameter" }
-  void g2 () noexcept (this->f()) { } // { dg-error "use of parameter" }
+  void g () noexcept (f()) { } // { dg-error ".this. is not a constant" }
+  void g2 () noexcept (this->f()) { } // { dg-error ".this. is not a constant" }
   void g3 () noexcept (b) { } // { dg-error "use of .this. in a constant expression|use of parameter" }
   void g4 (int i) noexcept (i) { } // { dg-error "use of parameter" }
-  void g5 () noexcept (A::f()) { } // { dg-error "use of parameter" }
+  void g5 () noexcept (A::f()) { } // { dg-error ".this. is not a constant" }
   void g6 () noexcept (foo(b)) { } // { dg-error "use of .this. in a constant expression|use of parameter" }
-  void g7 () noexcept (int{f()}) { } // { dg-error "use of parameter" }
+  void g7 () noexcept (int{f()}) { } // { dg-error ".this. is not a constant" }
 };
 
 int main ()
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept75.C b/gcc/testsuite/g++.dg/cpp0x/noexcept75.C
new file mode 100644
index 00000000000..d746f4768d0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept75.C
@@ -0,0 +1,17 @@
+// PR c++/94944
+// { dg-do compile { target c++11 } }
+
+template<class T>
+struct A {
+  void f();
+};
+
+template<class T>
+struct B : A<T> {
+  void g() noexcept(noexcept(A<T>::f()));
+};
+
+int main() {
+  B<int> b;
+  b.g();
+}