On Mon, Dec 02, 2019 at 02:29:56PM -0500, Jason Merrill wrote:
> On 11/27/19 6:38 PM, Jakub Jelinek wrote:
> > + if (i == 0 && DECL_VIRTUAL_P (fun))
> > + {
> > + tree addr = arg;
> > + STRIP_NOPS (addr);
> > + if (TREE_CODE (addr) == ADDR_EXPR)
> > + {
> > + tree obj = TREE_OPERAND (addr, 0);
> > + while (TREE_CODE (obj) == COMPONENT_REF
> > + && DECL_FIELD_IS_BASE (TREE_OPERAND (obj, 1)))
> > + obj = TREE_OPERAND (obj, 0);
>
> Shouldn't this loop stop when we reach DECL_CONTEXT (fun)?
I guess it can, patch I can test tonight attached. I thought it doesn't matter
much, because cxx_eval_indirect_ref would be able to go from further derived
class to the base if we want too far, but maybe that is not the case
with multiple inheritance.
> Relatedly, I notice that the OBJ_TYPE_REF code breaks with multiple
> inheritance: Adding a virtual function to Y in constexpr-virtual6.C leads to
I'm afraid I'd be lost with that. There is another bug in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92695#c12 about constexpr
defaulted virtual destructors not being synthetized until end of TU.
2019-12-02 Jakub Jelinek <ja...@redhat.com>
PR c++/92695
* constexpr.c (cxx_bind_parameters_in_call): For virtual calls,
adjust the first argument to point to the derived object rather
than its base.
* g++.dg/cpp2a/constexpr-virtual14.C: New test.
--- gcc/cp/constexpr.c.jj 2019-12-02 22:30:31.608306270 +0100
+++ gcc/cp/constexpr.c 2019-12-02 22:35:42.374501609 +0100
@@ -1441,6 +1441,26 @@ cxx_bind_parameters_in_call (const const
arg = adjust_temp_type (type, arg);
if (!TREE_CONSTANT (arg))
*non_constant_args = true;
+ /* For virtual calls, adjust the this argument, so that it is
+ the object on which the method is called, rather than
+ one of its bases. */
+ if (i == 0 && DECL_VIRTUAL_P (fun))
+ {
+ tree addr = arg;
+ STRIP_NOPS (addr);
+ if (TREE_CODE (addr) == ADDR_EXPR)
+ {
+ tree obj = TREE_OPERAND (addr, 0);
+ while (TREE_CODE (obj) == COMPONENT_REF
+ && DECL_FIELD_IS_BASE (TREE_OPERAND (obj, 1))
+ && !same_type_ignoring_top_level_qualifiers_p
+ (TREE_TYPE (obj), DECL_CONTEXT (fun)))
+ obj = TREE_OPERAND (obj, 0);
+ if (obj != TREE_OPERAND (addr, 0))
+ arg = build_fold_addr_expr_with_type (obj,
+ TREE_TYPE (arg));
+ }
+ }
TREE_VEC_ELT (binds, i) = arg;
}
parms = TREE_CHAIN (parms);
--- gcc/testsuite/g++.dg/cpp2a/constexpr-virtual14.C.jj 2019-12-02
22:34:05.554998508 +0100
+++ gcc/testsuite/g++.dg/cpp2a/constexpr-virtual14.C 2019-12-02
22:34:05.554998508 +0100
@@ -0,0 +1,27 @@
+// PR c++/92695
+// { dg-do compile { target c++2a } }
+
+struct A {
+ virtual int get () = 0;
+ virtual int set (A *o) = 0;
+};
+struct B : A {
+ constexpr int get () override { return 10; }
+ constexpr int set (A *o) override { a = o; return 20; }
+ A *a {};
+};
+constexpr auto addressof = [] (A &n) { return &n; };
+struct C {
+ B b;
+ A *c { addressof (b) };
+ constexpr int add () { return c->set (addressof (b)); }
+};
+struct D {
+ B b[2];
+ A *c { addressof (b[0]) };
+ constexpr int add () { return c->set (addressof (b[0])); }
+};
+template <typename T>
+constexpr int get () { T f; return f.add (); }
+static_assert (get<C> () == 20);
+static_assert (get<D> () == 20);
Jakub
