re PR c++/92695 (P1064R0 - virtual constexpr fails if object taken from array)

	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.

From-SVN: r278921

gcc/cp/ChangeLog

+2019-12-03  Jakub Jelinek  <jakub@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.
+
 2019-12-02  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/92695

gcc/cp/constexpr.c

@@ -1441,6 +1441,26 @@ cxx_bind_parameters_in_call (const constexpr_ctx *ctx, tree t,
 	    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/ChangeLog

+2019-12-03  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/92695
+	* g++.dg/cpp2a/constexpr-virtual14.C: New test.
+
 2019-12-03  Luo Xiong Hu  <luoxhu@linux.ibm.com>
 
 	* gcc.target/powerpc/pr72804.c: Fix missing space.

gcc/testsuite/g++.dg/cpp2a/constexpr-virtual14.C

+// 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);