Here we're incorrectly deeming the templated call a.g() inside b's
initializer as potentially constant, despite g being non-constexpr,
which leads to us wastefully instantiating the initializer ahead of time
and triggering a bug in access checking deferral (which will get fixed
in the subsequent patch).

This patch fixes this by calling get_fns earlier during potentiality
checking so that we also handle the templated form of a member function
call (whose overall callee is a COMPONENT_REF) when checking if the called
function is constexpr etc.

        PR c++/109480

gcc/cp/ChangeLog:

        * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>:
        Reorganize to call get_fns sooner.  Remove dead store to 'fun'.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the
        expected "without object" diagnostic isn't replaced by a
        "call to non-constexpr function" diagnostic.
        * g++.dg/template/non-dependent25.C: New test.
---
 gcc/cp/constexpr.cc                             | 16 ++++++++--------
 gcc/testsuite/g++.dg/cpp0x/noexcept59.C         |  2 +-
 gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++
 3 files changed, 23 insertions(+), 9 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index d1097764b10..29d872d0a5e 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool want_rval, 
bool strict, bool now,
 
        if (fun && is_overloaded_fn (fun))
          {
+           if (!RECUR (fun, true))
+             return false;
+           fun = get_fns (fun);
+
            if (TREE_CODE (fun) == FUNCTION_DECL)
              {
                if (builtin_valid_in_constant_expr_p (fun))
@@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool want_rval, 
bool strict, bool now,
                   expression the address will be folded away, so look
                   through it now.  */
                if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun)
-                   && !DECL_CONSTRUCTOR_P (fun))
+                   && !DECL_CONSTRUCTOR_P (fun)
+                   && !processing_template_decl)
                  {
                    tree x = get_nth_callarg (t, 0);
                    if (is_this_parameter (x))
@@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool 
want_rval, bool strict, bool now,
                    i = 1;
                  }
              }
-           else
-             {
-               if (!RECUR (fun, true))
-                 return false;
-               fun = get_first_fn (fun);
-             }
+
+           fun = OVL_FIRST (fun);
            /* Skip initial arguments to base constructors.  */
            if (DECL_BASE_CONSTRUCTOR_P (fun))
              i = num_artificial_parms_for (fun);
-           fun = DECL_ORIGIN (fun);
          }
        else if (fun)
           {
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C 
b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
index c752601ba09..1dc826d3111 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C
@@ -3,7 +3,7 @@
 
 template <class ...Ts> class A
 {
-  void e ();
+  constexpr bool e () { return true; };
   bool f (int() noexcept(this->e())); // { dg-error "this" }
   bool g (int() noexcept(e()));              // { dg-error "without object" }
 };
diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C 
b/gcc/testsuite/g++.dg/template/non-dependent25.C
new file mode 100644
index 00000000000..a2f9801e11f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent25.C
@@ -0,0 +1,14 @@
+// PR c++/109480
+
+template<class T>
+struct A {
+  void f() {
+    A<int> a;
+    const bool b = a.g();
+  }
+
+private:
+  bool g() const;
+};
+
+template struct A<int>;
-- 
2.40.1.459.g48d89b51b3

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