On Mar 1, 2018 4:57 PM, "Jason Merrill" <ja...@redhat.com> wrote:
> Ok.
>
> On Mar 1, 2018 4:40 PM, "Marek Polacek" <pola...@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 <pola...@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 <pola...@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 <
>> pola...@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 <pola...@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 <pola...@redhat.com>
>> > >> > Jason Merrill <ja...@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_ex
>> pression,
>> > > 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 <pola...@redhat.com>
>> Jason Merrill <ja...@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)
>
>
Actually, this is redundant; an expression can only be dependent if
processing_template_decl. I'll fix.
Jason
