[gcc/devel/omp/gcc-14] c++: memfn pointer as NTTP argument considered unused [PR119233]

[Tobias Burnus via Gcc-cvs]

https://gcc.gnu.org/g:f3e458b82b2fb72483ca48a06eadb22784d65b42

commit f3e458b82b2fb72483ca48a06eadb22784d65b42
Author: Patrick Palka <ppa...@redhat.com>
Date:   Tue Mar 18 11:38:33 2025 -0400

    c++: memfn pointer as NTTP argument considered unused [PR119233]
    
    This is just the member function pointer version of PR c++/105848,
    in which 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.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>
    (cherry picked from commit 51b1c0a2dde8ada0856c8a8cf2c1d26ac1657787)

Diff:
---
 gcc/cp/pt.cc                            |  6 ++++++
 gcc/testsuite/g++.dg/template/fn-ptr5.C | 28 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 0630557f5d27..45edf8d03971 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -22369,6 +22369,12 @@ 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 000000000000..db3113109ef9
--- /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>();
+}