From: Marek Polacek <polacek@redhat.com>
To: Jason Merrill <jason@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>, Andreas Schwab <schwab@suse.de>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: C++ PATCH to implement P1064R0, Virtual Function Calls in Constant Expressions (v4)
Date: Thu, 27 Sep 2018 23:18:00 -0000 [thread overview]
Message-ID: <20180927230841.GH5587@redhat.com> (raw)
In-Reply-To: <CADzB+2mVErikeJfPEFuAi9iiBRXqXgkM75CaRV7VT0sh3Mwtmg@mail.gmail.com>
On Thu, Sep 27, 2018 at 01:15:46AM -0400, Jason Merrill wrote:
> On Thu, Sep 20, 2018 at 5:20 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> > On Thu, Sep 20, 2018 at 09:12:53AM +0200, Andreas Schwab wrote:
> >> On Sep 19 2018, Jason Merrill <jason@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
next prev parent reply other threads:[~2018-09-27 23:08 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-14 17:21 C++ PATCH to implement P1064R0, Virtual Function Calls in Constant Expressions Marek Polacek
2018-09-14 17:41 ` Jakub Jelinek
2018-09-14 19:43 ` C++ PATCH to implement P1064R0, Virtual Function Calls in Constant Expressions (v2) Marek Polacek
2018-09-14 20:32 ` C++ PATCH to implement P1064R0, Virtual Function Calls in Constant Expressions Jason Merrill
2018-09-14 20:46 ` Marek Polacek
2018-09-17 21:51 ` Marek Polacek
2018-09-18 3:48 ` Jason Merrill
2018-09-18 15:37 ` C++ PATCH to implement P1064R0, Virtual Function Calls in Constant Expressions (v4) Marek Polacek
2018-09-18 18:36 ` Jason Merrill
2018-09-18 18:58 ` Marek Polacek
2018-09-19 13:27 ` Andreas Schwab
2018-09-19 14:19 ` Marek Polacek
2018-09-19 15:10 ` Andreas Schwab
2018-09-19 15:11 ` Marek Polacek
2018-09-19 17:35 ` Jason Merrill
2018-09-20 8:26 ` Andreas Schwab
2018-09-20 9:23 ` Jakub Jelinek
2018-09-27 7:16 ` Jason Merrill
2018-09-27 23:18 ` Marek Polacek [this message]
2018-09-28 5:44 ` Jason Merrill
2018-09-28 6:48 ` Jakub Jelinek
2018-12-08 9:07 ` [C++ PATCH] FIx constexpr virtual function call handling on ia64 (PR c++/87861) Jakub Jelinek
2018-12-11 18:53 ` Jason Merrill
2018-10-08 14:18 ` C++ PATCH to implement P1064R0, Virtual Function Calls in Constant Expressions (v4) Andreas Schwab
2018-10-10 11:53 ` Jakub Jelinek
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