On Mon, 16 Aug 2021, Marek Polacek wrote:
> On Mon, Aug 16, 2021 at 03:06:08PM -0400, Patrick Palka via Gcc-patches wrote:
> > During aggregate CTAD, collect_ctor_idx_types always recurses into a
> > sub-CONSTRUCTOR, regardless of whether the corresponding pair of braces
> > was elided in the original initializer. This causes us to reject some
> > completely-braced forms of aggregate CTAD as in the first testcase
> > below, because collect_ctor_idx_types effectively assumes that the given
> > initializer is always minimally-braced (hence the aggregate deduction
> > candidate is given a function type that's incompatible with the written
> > initializer).
> >
> > This patch fixes this by making reshape_init flag CONSTRUCTORs that
> > were built to undo brace elision in the original CONSTRUCTOR, so that
> > collect_ctor_idx_types can determine whether to recurse into a
> > sub-CONSTRUCTOR by simply inspecting this flag.
> >
> > This happens to also fix PR101820, which is about aggregate CTAD using
> > designated initializers, for a similar reason as above.
> >
> > A tricky case is the "intermediately-braced" initialization of 'e3'
> > in the first testcase below. It seems to me we're correct to continue
> > to reject this according to [over.match.class.deduct]/1 because here
> > the initializer element {1, 2, 3, 4} corresponds to the subobject E::t,
> > hence the type T_1 of the first funciton parameter of the aggregate
> > deduction candidate is T(&&)[2][2] which the argument {1, 2, 3, 4} isn't
> > compatible with (as opposed to say T(&&)[4]).
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk/11?
> >
> > PR c++/101344
> > PR c++/101820
> >
> > gcc/cp/ChangeLog:
> >
> > * cp-tree.h (CONSTRUCTOR_BRACES_ELIDED_P): Define.
> > * decl.c (reshape_init_r): Set it.
> > * pt.c (collect_ctor_idx_types): Recurse into a sub-CONSTRUCTOR
> > iff CONSTRUCTOR_BRACES_ELIDED_P.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp2a/class-deduction-aggr11.C: New test.
> > * g++.dg/cpp2a/class-deduction-aggr12.C: New test.
> > ---
> > gcc/cp/cp-tree.h | 6 ++++
> > gcc/cp/decl.c | 18 +++++++++---
> > gcc/cp/pt.c | 7 +----
> > .../g++.dg/cpp2a/class-deduction-aggr11.C | 29 +++++++++++++++++++
> > .../g++.dg/cpp2a/class-deduction-aggr12.C | 15 ++++++++++
> > 5 files changed, 65 insertions(+), 10 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr11.C
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr12.C
> >
> > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> > index bd3f12a393e..8cbf6cc30b0 100644
> > --- a/gcc/cp/cp-tree.h
> > +++ b/gcc/cp/cp-tree.h
> > @@ -4502,6 +4502,12 @@ more_aggr_init_expr_args_p (const
> > aggr_init_expr_arg_iterator *iter)
> > #define CONSTRUCTOR_IS_PAREN_INIT(NODE) \
> > (CONSTRUCTOR_CHECK(NODE)->base.private_flag)
> >
> > +/* True if reshape_init built this CONSTRUCTOR to undo the brace elision
> > + of another CONSTRUCTOR. This flag is used during C++20 aggregate
> > + CTAD. */
> > +#define CONSTRUCTOR_BRACES_ELIDED_P(NODE) \
> > + (CONSTRUCTOR_CHECK (NODE)->base.protected_flag)
> > +
> > /* True if NODE represents a conversion for direct-initialization in a
> > template. Set by perform_implicit_conversion_flags. */
> > #define IMPLICIT_CONV_EXPR_DIRECT_INIT(NODE) \
> > diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> > index b3671ee8956..9e257b32e18 100644
> > --- a/gcc/cp/decl.c
> > +++ b/gcc/cp/decl.c
> > @@ -6650,7 +6650,8 @@ reshape_init_r (tree type, reshape_iter *d, tree
> > first_initializer_p,
> > /* A non-aggregate type is always initialized with a single
> > initializer. */
> > if (!CP_AGGREGATE_TYPE_P (type)
> > - /* As is an array with dependent bound. */
> > + /* As is an array with dependent bound, which we can see
> > + during C++20 aggregate CTAD. */
> > || (cxx_dialect >= cxx20
> > && TREE_CODE (type) == ARRAY_TYPE
> > && uses_template_parms (TYPE_DOMAIN (type))))
> > @@ -6767,6 +6768,7 @@ reshape_init_r (tree type, reshape_iter *d, tree
> > first_initializer_p,
> > initializer already, and there is not a CONSTRUCTOR, it means that
> > there
> > is a missing set of braces (that is, we are processing the case for
> > which reshape_init exists). */
> > + bool braces_elided_p = false;
> > if (!first_initializer_p)
> > {
> > if (TREE_CODE (stripped_init) == CONSTRUCTOR)
> > @@ -6802,17 +6804,25 @@ reshape_init_r (tree type, reshape_iter *d, tree
> > first_initializer_p,
> > warning (OPT_Wmissing_braces,
> > "missing braces around initializer for %qT",
> > type);
> > + braces_elided_p = true;
> > }
> >
> > /* Dispatch to specialized routines. */
> > + tree new_init;
> > if (CLASS_TYPE_P (type))
> > - return reshape_init_class (type, d, first_initializer_p, complain);
> > + new_init = reshape_init_class (type, d, first_initializer_p, complain);
> > else if (TREE_CODE (type) == ARRAY_TYPE)
> > - return reshape_init_array (type, d, first_initializer_p, complain);
> > + new_init = reshape_init_array (type, d, first_initializer_p, complain);
> > else if (VECTOR_TYPE_P (type))
> > - return reshape_init_vector (type, d, complain);
> > + new_init = reshape_init_vector (type, d, complain);
> > else
> > gcc_unreachable();
> > +
> > + if (braces_elided_p)
> > + if (TREE_CODE (new_init) == CONSTRUCTOR)
> > + CONSTRUCTOR_BRACES_ELIDED_P (new_init) = 1;
>
> Any reason for the two ifs and not an &&?
Whoops, that's a refactoring artifact from an earlier version of the
patch. Fixed now.
>
> Marek
>
>
