[PATCH 1/2] c++: potentiality of templated memfn call [PR109480]

[Patrick Palka <ppalka@redhat.com>]

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