From: Jason Merrill <jason@redhat.com>
To: Marek Polacek <polacek@redhat.com>
Cc: gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: C++ PATCH to fix static init with () in a template (PR c++/84582)
Date: Thu, 01 Mar 2018 21:57:00 -0000 [thread overview]
Message-ID: <CADzB+2kgmi-hWUTGf9BRyMY_7zkAULo1nnV4LbM3bi=RaRnY1A@mail.gmail.com> (raw)
In-Reply-To: <20180301214004.GG16833@redhat.com>
Ok.
On Mar 1, 2018 4:40 PM, "Marek Polacek" <polacek@redhat.com> wrote:
> On Thu, Mar 01, 2018 at 01:56:50PM -0500, Jason Merrill wrote:
> > On Thu, Mar 1, 2018 at 8:17 AM, Marek Polacek <polacek@redhat.com>
> wrote:
> > > On Wed, Feb 28, 2018 at 04:50:39PM -0500, Jason Merrill wrote:
> > >> On Wed, Feb 28, 2018 at 4:19 PM, Marek Polacek <polacek@redhat.com>
> wrote:
> > >> > On Wed, Feb 28, 2018 at 10:51:17AM -0500, Jason Merrill wrote:
> > >> >> On Wed, Feb 28, 2018 at 9:32 AM, Marek Polacek <polacek@redhat.com>
> wrote:
> > >> >> > On Tue, Feb 27, 2018 at 04:16:31PM -0500, Jason Merrill wrote:
> > >> >> >> On 02/27/2018 02:13 PM, Marek Polacek wrote:
> > >> >> >> > My recent change introducing cxx_constant_init caused this
> code
> > >> >> >> >
> > >> >> >> > template <class> class A {
> > >> >> >> > static const long b = 0;
> > >> >> >> > static const unsigned c = (b);
> > >> >> >> > };
> > >> >> >> >
> > >> >> >> > to be rejected. The reason is that force_paren_expr turns
> "b" into "*(const
> > >> >> >> > long int &) &b", where the former is not value-dependent but
> the latter is
> > >> >> >> > value-dependent. So when we get to maybe_constant_init_1:
> > >> >> >> > 5147 if (!is_nondependent_static_init_expression (t))
> > >> >> >> > 5148 /* Don't try to evaluate it. */;
> > >> >> >> > it's not evaluated and we get the non-constant initialization
> error.
> > >> >> >> > (Before we'd always evaluated the expression.)
> > >> >> >> >
> > >> >> >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > >> >> >> >
> > >> >> >> > 2018-02-27 Marek Polacek <polacek@redhat.com>
> > >> >> >> >
> > >> >> >> > PR c++/84582
> > >> >> >> > * semantics.c (force_paren_expr): Avoid creating a static
> cast
> > >> >> >> > when processing a template.
> > >> >> >> >
> > >> >> >> > * g++.dg/cpp1z/static1.C: New test.
> > >> >> >> > * g++.dg/template/static37.C: New test.
> > >> >> >> >
> > >> >> >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > >> >> >> > index 35569d0cb0d..b48de2df4e2 100644
> > >> >> >> > --- gcc/cp/semantics.c
> > >> >> >> > +++ gcc/cp/semantics.c
> > >> >> >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree expr)
> > >> >> >> > expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> > >> >> >> > else if (VAR_P (expr) && DECL_HARD_REGISTER (expr))
> > >> >> >> > /* We can't bind a hard register variable to a
> reference. */;
> > >> >> >> > - else
> > >> >> >> > + else if (!processing_template_decl)
> > >> >> >>
> > >> >> >> Hmm, this means that we forget about the parentheses in a
> template. I'm
> > >> >> >> surprised that this didn't break anything in the testsuite. In
> particular,
> > >> >> >> auto-fn15.C. I've attached an addition to auto-fn15.C to catch
> this issue.
> > >> >> >
> > >> >> > Thanks, you're right. I'll use it.
> > >> >> >
> > >> >> >> Can we use PAREN_EXPR instead of the static_cast in a template?
> > >> >> >
> > >> >> > I don't think so, it would fix the issue you pointed out in
> auto-fn15.C but
> > >> >> > it wouldn't fix the original test. The problem with using
> PAREN_EXPR in a
> > >> >> > template is that instantiate_non_dependent_expr will turn in
> into the
> > >> >> > static cast anyway; tsubst_copy_and_build has
> > >> >> > case PAREN_EXPR:
> > >> >> > RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t,
> 0))));
> > >> >> > so it calls force_paren_expr and this time we're not in a
> template. And
> > >> >> > then when calling cxx_constant_init we have the same issue.
> > >> >>
> > >> >> Then maybe we need something like fold_non_dependent_expr, which
> > >> >> checks for dependency before substitution and then immediately
> > >> >> evaluates the result.
> > >> >
> > >> > I hope you meant something like this. Further testing also
> revealed that
> > >> > maybe_undo_parenthesized_ref should be able to unwrap PAREN_EXPR
> (so that
> > >> > (fn1)(); in paren2.C is handled correctly), and that lvalue_kind
> should look
> > >> > into PAREN_EXPR so as to give the correct answer regarding
> lvalueness: we
> > >> > should accept
> > >> >
> > >> > template<typename T>
> > >> > void foo (int i)
> > >> > {
> > >> > ++(i);
> > >> > }
> > >> >
> > >> > Apologies if I'm on the wrong track.
> > >> >
> > >> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > >> >
> > >> > 2018-02-28 Marek Polacek <polacek@redhat.com>
> > >> > Jason Merrill <jason@redhat.com>
> > >> >
> > >> > PR c++/84582
> > >> > * semantics.c (force_paren_expr): Avoid creating the static
> cast
> > >> > when in a template. Create a PAREN_EXPR when in a template.
> > >> > (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
> > >> > * typeck2.c (store_init_value): Call
> fold_non_dependent_expr instead
> > >> > of instantiate_non_dependent_expr.
> > >> > * tree.c (lvalue_kind): Handle PAREN_EXPR like
> NON_DEPENDENT_EXPR.
> > >> >
> > >> > * g++.dg/cpp1y/auto-fn15.C: Extend testing.
> > >> > * g++.dg/cpp1z/static1.C: New test.
> > >> > * g++.dg/template/static37.C: New test.
> > >> >
> > >> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > >> > index 35569d0cb0d..722e3718a14 100644
> > >> > --- gcc/cp/semantics.c
> > >> > +++ gcc/cp/semantics.c
> > >> > @@ -1697,7 +1697,7 @@ force_paren_expr (tree expr)
> > >> > expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> > >> > else if (VAR_P (expr) && DECL_HARD_REGISTER (expr))
> > >> > /* We can't bind a hard register variable to a reference. */;
> > >> > - else
> > >> > + else if (!processing_template_decl)
> > >> > {
> > >> > cp_lvalue_kind kind = lvalue_kind (expr);
> > >> > if ((kind & ~clk_class) != clk_none)
> > >> > @@ -1713,6 +1713,8 @@ force_paren_expr (tree expr)
> > >> > REF_PARENTHESIZED_P (expr) = true;
> > >> > }
> > >> > }
> > >> > + else
> > >> > + expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> > >>
> > >> There's already a branch for building PAREN_EXPR, let's just replace
> > >> its condition.
> > >
> > > Sure.
> > >
> > >> > - value = instantiate_non_dependent_expr (value);
> > >> > + value = fold_non_dependent_expr (value);
> > >>
> > >> I was thinking that we want a parallel fold_non_dependent_init (that
> > >> hopefully shares most of the implementation). Then we shouldn't need
> > >> the call to maybe_constant_init anymore.
> > >
> > > If you mean fold_non_dependent_init that would be like
> fold_non_dependent_expr
> > > but with maybe_constant_init and not maybe_constant_value
> >
> > And is_nondependent_static_init_expression, and different arguments to
> > cxx_eval_outermost_constant_expression, yes.
>
> Ah. Maybe it'll be useful sometime in the future.
>
> > > then that would break e.g.
> > >
> > > const double d = 9.0; // missing constexpr
> > > constexpr double j = d; // should give error
> > >
> > > because maybe_constant_value checks is_nondependent_constant_expression,
> and
> > > "d" in the example above is not a constant expression, so we don't
> evaluate,
> > > and "d" stays "d", so require_constant_expression gives the error. On
> the
> > > other hand, maybe_constant_init checks is_nondependent_static_init_
> expression,
> > > and "d" is that, so we evaluate "d" to "9.0". Then
> require_constant_expression
> > > doesn't complain.
> >
> > Ah, I see. You're right, let's stick with fold_non_dependent_expr.
>
> Thanks, so this is the final patch then:
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-03-01 Marek Polacek <polacek@redhat.com>
> Jason Merrill <jason@redhat.com>
>
> PR c++/84582
> * semantics.c (force_paren_expr): Create a PAREN_EXPR when in
> a template.
> (maybe_undo_parenthesized_ref): Unwrap PAREN_EXPR.
> * typeck2.c (store_init_value): Call fold_non_dependent_expr
> instead
> of instantiate_non_dependent_expr.
> * tree.c (lvalue_kind): Handle PAREN_EXPR like NON_DEPENDENT_EXPR.
>
> * g++.dg/cpp1y/auto-fn15.C: Extend testing.
> * g++.dg/cpp1z/static1.C: New test.
> * g++.dg/template/static37.C: New test.
>
> diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> index 87c5c669a55..1ac1d23e761 100644
> --- gcc/cp/semantics.c
> +++ gcc/cp/semantics.c
> @@ -1693,7 +1693,8 @@ force_paren_expr (tree expr)
> if (TREE_CODE (expr) == COMPONENT_REF
> || TREE_CODE (expr) == SCOPE_REF)
> REF_PARENTHESIZED_P (expr) = true;
> - else if (type_dependent_expression_p (expr))
> + else if (type_dependent_expression_p (expr)
> + || processing_template_decl)
> expr = build1 (PAREN_EXPR, TREE_TYPE (expr), expr);
> else if (VAR_P (expr) && DECL_HARD_REGISTER (expr))
> /* We can't bind a hard register variable to a reference. */;
> @@ -1724,9 +1725,10 @@ force_paren_expr (tree expr)
> tree
> maybe_undo_parenthesized_ref (tree t)
> {
> - if (cxx_dialect >= cxx14
> - && INDIRECT_REF_P (t)
> - && REF_PARENTHESIZED_P (t))
> + if (cxx_dialect < cxx14)
> + return t;
> +
> + if (INDIRECT_REF_P (t) && REF_PARENTHESIZED_P (t))
> {
> t = TREE_OPERAND (t, 0);
> while (TREE_CODE (t) == NON_LVALUE_EXPR
> @@ -1737,6 +1739,8 @@ maybe_undo_parenthesized_ref (tree t)
> || TREE_CODE (t) == STATIC_CAST_EXPR);
> t = TREE_OPERAND (t, 0);
> }
> + else if (TREE_CODE (t) == PAREN_EXPR)
> + t = TREE_OPERAND (t, 0);
>
> return t;
> }
> diff --git gcc/cp/tree.c gcc/cp/tree.c
> index 9b9e36a1173..19f1c0629c9 100644
> --- gcc/cp/tree.c
> +++ gcc/cp/tree.c
> @@ -239,6 +239,7 @@ lvalue_kind (const_tree ref)
> return lvalue_kind (BASELINK_FUNCTIONS (CONST_CAST_TREE (ref)));
>
> case NON_DEPENDENT_EXPR:
> + case PAREN_EXPR:
> return lvalue_kind (TREE_OPERAND (ref, 0));
>
> case VIEW_CONVERT_EXPR:
> diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
> index 153b46cca77..583c65d4d0a 100644
> --- gcc/cp/typeck2.c
> +++ gcc/cp/typeck2.c
> @@ -822,7 +822,7 @@ store_init_value (tree decl, tree init, vec<tree,
> va_gc>** cleanups, int flags)
> if (decl_maybe_constant_var_p (decl) || TREE_STATIC (decl))
> {
> bool const_init;
> - value = instantiate_non_dependent_expr (value);
> + value = fold_non_dependent_expr (value);
> if (DECL_DECLARED_CONSTEXPR_P (decl)
> || (DECL_IN_AGGR_P (decl) && !DECL_VAR_DECLARED_INLINE_P (decl)))
> {
> diff --git gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> index ba9f3579f62..0db428f7270 100644
> --- gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> +++ gcc/testsuite/g++.dg/cpp1y/auto-fn15.C
> @@ -22,6 +22,8 @@ template <class T>
> decltype(auto) h5(T t) { return t.i; }
> template <class T>
> decltype(auto) h6(T t) { return (t.i); }
> +template <class T>
> +decltype(auto) h7(T t) { return (i); }
>
> int main()
> {
> @@ -48,4 +50,5 @@ int main()
> same_type<decltype(h4()),int&>();
> same_type<decltype(h5(a)),int>();
> same_type<decltype(h6(a)),int&>();
> + same_type<decltype(h7(a)),int&>();
> }
> diff --git gcc/testsuite/g++.dg/cpp1z/static1.C
> gcc/testsuite/g++.dg/cpp1z/static1.C
> index e69de29bb2d..cb872997c5a 100644
> --- gcc/testsuite/g++.dg/cpp1z/static1.C
> +++ gcc/testsuite/g++.dg/cpp1z/static1.C
> @@ -0,0 +1,19 @@
> +// PR c++/84582
> +// { dg-options -std=c++17 }
> +
> +class C {
> + static inline const long b = 0;
> + static inline const unsigned c = (b);
> +};
> +class D {
> + static inline const long b = 0;
> + static inline const unsigned c = b;
> +};
> +template <class> class A {
> + static inline const long b = 0;
> + static inline const unsigned c = (b);
> +};
> +template <class> class B {
> + static inline const long b = 0;
> + static inline const unsigned c = b;
> +};
> diff --git gcc/testsuite/g++.dg/template/static37.C
> gcc/testsuite/g++.dg/template/static37.C
> index e69de29bb2d..90bc65d2fbc 100644
> --- gcc/testsuite/g++.dg/template/static37.C
> +++ gcc/testsuite/g++.dg/template/static37.C
> @@ -0,0 +1,18 @@
> +// PR c++/84582
> +
> +class C {
> + static const long b = 0;
> + static const unsigned c = (b);
> +};
> +class D {
> + static const long b = 0;
> + static const unsigned c = b;
> +};
> +template <class> class A {
> + static const long b = 0;
> + static const unsigned c = (b);
> +};
> +template <class> class B {
> + static const long b = 0;
> + static const unsigned c = b;
> +};
>
> Marek
>
next prev parent reply other threads:[~2018-03-01 21:57 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 19:13 Marek Polacek
2018-02-27 21:16 ` Jason Merrill
2018-02-28 14:32 ` Marek Polacek
2018-02-28 15:51 ` Jason Merrill
2018-02-28 21:19 ` Marek Polacek
2018-02-28 21:51 ` Jason Merrill
2018-03-01 13:17 ` Marek Polacek
2018-03-01 18:57 ` Jason Merrill
2018-03-01 21:40 ` Marek Polacek
2018-03-01 21:57 ` Jason Merrill [this message]
2018-03-02 18:18 ` Jason Merrill
2018-03-02 18:20 ` Marek Polacek
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