On Thu, Sep 27, 2018 at 01:15:46AM -0400, Jason Merrill wrote:
> On Thu, Sep 20, 2018 at 5:20 AM, Jakub Jelinek <ja...@redhat.com> wrote:
> > On Thu, Sep 20, 2018 at 09:12:53AM +0200, Andreas Schwab wrote:
> >> On Sep 19 2018, Jason Merrill <ja...@redhat.com> wrote:
> >>
> >> > Andreas, do the new testcases pass? That would surprise me, but OK if
> >> > so.
> >>
> >> No, they don't.
> >>
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:29:26:
> >> error: non-constant condition for static assertion
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:29:23:
> >> error: expression '((& X2::_ZTV2X2) + 16)' does not designate a
> >> 'constexpr' function
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:33:26:
> >> error: non-constant condition for static assertion
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:33:23:
> >> error: expression '((& X2::_ZTV2X2) + 16)' does not designate a
> >> 'constexpr' function
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:37:27:
> >> error: non-constant condition for static assertion
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:37:24:
> >> error: expression '((& X2::_ZTV2X2) + 16)' does not designate a
> >> 'constexpr' function
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:41:26:
> >> error: non-constant condition for static assertion
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:41:23:
> >> error: expression '((& X4::_ZTV2X4) + 16)' does not designate a
> >> 'constexpr' function
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:45:26:
> >> error: non-constant condition for static assertion
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:45:23:
> >> error: expression '((& X4::_ZTV2X4) + 16)' does not designate a
> >> 'constexpr' function
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:49:27:
> >> error: non-constant condition for static assertion
> >> /usr/local/gcc/gcc-20180920/gcc/testsuite/g++.dg/cpp2a/constexpr-virtual2.C:49:24:
> >> error: expression '((& X4::_ZTV2X4) + 16)' does not designate a
> >> 'constexpr' function
> >> compiler exited with status 1
> >> FAIL: g++.dg/cpp2a/constexpr-virtual2.C (test for excess errors)
> >
> > I think the primary problem here is:
> > /* When using function descriptors, the address of the
> > vtable entry is treated as a function pointer. */
> > if (TARGET_VTABLE_USES_DESCRIPTORS)
> > e2 = build1 (NOP_EXPR, TREE_TYPE (e2),
> > cp_build_addr_expr (e2, complain));
> > in typeck.c, on non-descriptor targets we have an INDIRECT_REF where we
> > read the vtable function pointer. On ia64, the above optimizes the
> > INDIRECT_REF away, so what the cxx_eval_call_expression actually gets
> > after constexpr evaluating the CALL_FN is not ADDR_EXPR of a function,
> > but the address of the function descriptor (e.g. &_ZTV2X2 + 16 ).
> >
> > So, perhaps in cxx_eval_call_expression we need:
> > if (TREE_CODE (fun) == ADDR_EXPR)
> > fun = TREE_OPERAND (fun, 0);
> > + else if (TARGET_VTABLE_USES_DESCRIPTORS
> > + && TREE_CODE (fun) == POINTER_PLUS_EXPR
> > + && ...)
> > where we verify that p+ first argument is ADDR_EXPR of a virtual table,
> > second arg is INTEGER_CST and just walk the DECL_INITIAL of that, finding
> > the FDESC_EXPR at the right offset (therefore, I believe you need following
> > rather than the patch you've posted, so that you can actually find it) and
> > finally pick the function from the FDESC_EXPR entry.
> > Makes me wonder what happens with indirect calls in constexpr evaluation,
> > e.g. if I do:
> > constexpr int bar () { return 42; }
> > constexpr int foo () { int (*fn) () = bar; return fn (); }
> > static_assert (foo () == 42);
> > but apparently this works.
> >
> > --- gcc/cp/class.c.jj 2018-09-20 09:56:59.229751895 +0200
> > +++ gcc/cp/class.c 2018-09-20 10:12:17.447370890 +0200
> > @@ -9266,7 +9266,6 @@ build_vtbl_initializer (tree binfo,
> > tree vcall_index;
> > tree fn, fn_original;
> > tree init = NULL_TREE;
> > - tree idx = size_int (jx++);
> >
> > fn = BV_FN (v);
> > fn_original = fn;
> > @@ -9370,7 +9369,7 @@ build_vtbl_initializer (tree binfo,
> > int i;
> > if (init == size_zero_node)
> > for (i = 0; i < TARGET_VTABLE_USES_DESCRIPTORS; ++i)
> > - CONSTRUCTOR_APPEND_ELT (*inits, idx, init);
> > + CONSTRUCTOR_APPEND_ELT (*inits, size_int (jx++), init);
> > else
> > for (i = 0; i < TARGET_VTABLE_USES_DESCRIPTORS; ++i)
> > {
> > @@ -9378,11 +9377,11 @@ build_vtbl_initializer (tree binfo,
> > fn, build_int_cst (NULL_TREE, i));
> > TREE_CONSTANT (fdesc) = 1;
> >
> > - CONSTRUCTOR_APPEND_ELT (*inits, idx, fdesc);
> > + CONSTRUCTOR_APPEND_ELT (*inits, size_int (jx++), fdesc);
> > }
> > }
> > else
> > - CONSTRUCTOR_APPEND_ELT (*inits, idx, init);
> > + CONSTRUCTOR_APPEND_ELT (*inits, size_int (jx++), init);
> > }
> > }
>
> This patch is OK. And your suggestion for cxx_eval_call_expression
> sounds right, too. Marek, will you follow up on that?
Ok, I will (provided I can get a box that has TARGET_VTABLE_USES_DESCRIPTORS, I
think ppc64 BE should be enough).
Marek
