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

[Simon Martin]

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 teaches cxx_bind_parameters_in_call to handle the __in_chrg
and __vtt_parm parameters that {con,de}structors might have.

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].

Successfully tested on x86_64-pc-linux-gnu.

        PR c++/116722

gcc/cp/ChangeLog:

        * constexpr.cc (cxx_bind_parameters_in_call): Leave artificial
        constructor parameters as is.

gcc/testsuite/ChangeLog:

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

---
 gcc/cp/constexpr.cc                           | 10 +++++++++-
 gcc/testsuite/g++.dg/cpp0x/constexpr-ctor22.C | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-ctor22.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index f6fd059be46..815f93b1d47 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1871,13 +1871,21 @@ 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))
        {
          x = ctx->object;
          x = build_address (x);
        }
+      /* Leave the __in_chrg and __vtt_parm parameters of *structors of classes
+        with virtual bases as is.  */
+      if ((i == 1 && DECL_HAS_IN_CHARGE_PARM_P (fun))
+         || (i == 2 && DECL_HAS_VTT_PARM_P (fun)))
+       {
+         TREE_VEC_ELT (binds, i) = arg;
+         continue;
+       }
       if (TREE_ADDRESSABLE (type))
        {
          /* Undo convert_for_arg_passing work here.  */
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 00000000000..279f6ec4454
--- /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.);
+}
-- 
2.44.0