c++: Don't ICE due to artificial constructor parameters [PR116722]

The following code triggers an ICE

=== cut here ===
class base {};
class derived : virtual public base {
public:
  template<typename Arg> constexpr derived(Arg) {}
};
int main() {
  derived obj(1.);
}
=== cut here ===

The problem is that cxx_bind_parameters_in_call ends up attempting to
convert a REAL_CST (the first non artificial parameter) to INTEGER_TYPE
(the type of the __in_chrg parameter), which ICEs.

This patch changes cxx_bind_parameters_in_call to return early if it's
called with a *structor that has an __in_chrg or __vtt_parm parameter
since the expression won't be a constant expression.

Note that in the test case, the constructor is not constexpr-suitable,
however it's OK since it's a template according to my read of paragraph
(3) of [dcl.constexpr].

	PR c++/116722

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_bind_parameters_in_call): Leave early for
	{con,de}structors of classes with virtual bases.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-ctor22.C: New test.

2 files changed, 25 insertions, 1 deletions

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index f6fd059..5c66967 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1862,6 +1862,15 @@ cxx_bind_parameters_in_call (const constexpr_ctx *ctx, tree t, tree fun,
   int nparms = list_length (parms);
   int nbinds = nargs < nparms ? nargs : nparms;
   tree binds = make_tree_vec (nbinds);
+
+  /* The call is not a constant expression if it involves the cdtor for a type
+     with virtual bases.  */
+  if (DECL_HAS_IN_CHARGE_PARM_P (fun) || DECL_HAS_VTT_PARM_P (fun))
+    {
+      *non_constant_p = true;
+      return binds;
+    }
+
   for (i = 0; i < nargs; ++i)
     {
       tree x, arg;
@@ -1871,7 +1880,7 @@ cxx_bind_parameters_in_call (const constexpr_ctx *ctx, tree t, tree fun,
       x = get_nth_callarg (t, i);
       /* For member function, the first argument is a pointer to the implied
          object.  For a constructor, it might still be a dummy object, in
-         which case we get the real argument from ctx. */
+	 which case we get the real argument from ctx.  */
       if (i == 0 && DECL_CONSTRUCTOR_P (fun)
 	  && is_dummy_object (x))
 	{
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-ctor22.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-ctor22.C
new file mode 100644
index 0000000..279f6ec
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-ctor22.C
@@ -0,0 +1,15 @@
+// PR c++/116722
+// We're now accepting this in spite of the virtual base class. This is OK
+// according to [dcl.constexpr] 3: "Except for instantiated constexpr functions
+// non-templated constexpr functions shall be constexpr-suitable".
+// { dg-do compile { target c++11 } }
+
+class base {};
+class derived : virtual public base {
+public:
+  template<typename Arg>
+  constexpr derived(Arg) {}
+};
+int main() {
+  derived obj(1.);
+}