[PATCH] c++: memfn pointer as NTTP argument considered unused [PR119233]

[Patrick Palka]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
OK for trunk/backports?

-- >8 --

This is just the member function pointer version of PR c++/105848,
wherein our non-dependent call pruning may cause us to not mark an
otherwise unused function pointer template argument as used.

        PR c++/119233

gcc/cp/ChangeLog:

        * pt.cc (mark_template_arguments_used): Also handle member
        function pointers.

gcc/testsuite/ChangeLog:

        * g++.dg/template/fn-ptr5.C: New test.
---
 gcc/cp/pt.cc                            |  6 ++++++
 gcc/testsuite/g++.dg/template/fn-ptr5.C | 28 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr5.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 8aaae446868..50eda189c43 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -22491,6 +22491,12 @@ mark_template_arguments_used (tree tmpl, tree args)
              gcc_checking_assert (ok || seen_error ());
            }
        }
+      /* A member function pointer.  */
+      else if (TREE_CODE (arg) == PTRMEM_CST)
+       {
+         bool ok = mark_used (PTRMEM_CST_MEMBER (arg), tf_none);
+         gcc_checking_assert (ok || seen_error ());
+       }
       /* A class NTTP argument.  */
       else if (VAR_P (arg)
               && DECL_NTTP_OBJECT_P (arg))
diff --git a/gcc/testsuite/g++.dg/template/fn-ptr5.C 
b/gcc/testsuite/g++.dg/template/fn-ptr5.C
new file mode 100644
index 00000000000..db3113109ef
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/fn-ptr5.C
@@ -0,0 +1,28 @@
+// PR c++/119233
+// A version of fn-ptr3a.C using member instead of non-member function
+// pointers.
+
+struct B {
+  template<class T>
+  void f(T) { T::fail; } // { dg-error "fail" }
+};
+
+template<void (B::*P)(int)>
+struct A {
+  // P not called
+};
+
+template<void (B::*P)(char)>
+void wrap() {
+  // P not called
+}
+
+template<int>
+void g() {
+  A<&B::f> a; // { dg-message "required from" }
+  wrap<&B::f>(); // { dg-message "required from" }
+}
+
+int main() {
+  g<0>();
+}
-- 
2.49.0.rc1.37.ge969bc8759