On Mon, Jan 21, 2019 at 03:14:53PM -0500, Jason Merrill wrote:
> On 1/18/19 9:12 AM, Marek Polacek wrote:
> > On Thu, Jan 17, 2019 at 04:17:29PM -0500, Jason Merrill wrote:
> > > On 1/17/19 2:09 PM, Marek Polacek wrote:
> > > > This patch ought to fix the rest of 78244, a missing narrowing warning
> > > > in
> > > > decltype.
> > > >
> > > > As I explained in Bugzilla, there can be three scenarios:
> > > >
> > > > 1) decltype is in a template and it has no dependent expressions, which
> > > > is the problematical case. finish_compound_literal just returns the
> > > > compound literal without checking narrowing if processing_template_decl.
> > >
> > > This is the sort of thing that we've been gradually fixing: if the
> > > compound
> > > literal isn't dependent at all, we want to do the normal processing. And
> > > then usually return a result based on the original trees rather than the
> > > result of processing. For instance, finish_call_expr. Something like
> > > that
> > > ought to work here, too, and be more generally applicable; this shouldn't
> > > be
> > > limited to casting to a scalar type, casting to a known class type can
> > > also
> > > involve narrowing.
> >
> > Great, that works just fine. I also had to check if the type is
> > type-dependent, otherwise complete_type could fail.
> >
> > > The check in the other patch that changes instantiation_dependent_r should
> > > be more similar to the one in finish_compound_literal. Or perhaps you
> > > could
> > > set a flag here in finish_compound_literal to indicate that it's
> > > instantiation-dependent, and just check that in instantiation_dependent_r.
> >
> > Done, but I feel bad about adding another flag. But I guess it's cheaper
> > this way. Thanks!
> >
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >
> > 2019-01-18 Marek Polacek <pola...@redhat.com>
> >
> > PR c++/88815 - narrowing conversion lost in decltype.
> > PR c++/78244 - narrowing conversion in template not detected.
> > * cp-tree.h (CONSTRUCTOR_IS_DEPENDENT): New.
> > * pt.c (instantiation_dependent_r): Consider a CONSTRUCTOR with
> > CONSTRUCTOR_IS_DEPENDENT instantiation-dependent.
> > * semantics.c (finish_compound_literal): When the compound literal
> > isn't instantiation-dependent and the type isn't type-dependent,
> > fall back to the normal processing. Don't only call check_narrowing
> > for scalar types. Set CONSTRUCTOR_IS_DEPENDENT.
> >
> > * g++.dg/cpp0x/Wnarrowing15.C: New test.
> > * g++.dg/cpp0x/constexpr-decltype3.C: New test.
> > * g++.dg/cpp1y/Wnarrowing1.C: New test.
> >
> > diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
> > index 5cc8f88d522..778874cccd6 100644
> > --- gcc/cp/cp-tree.h
> > +++ gcc/cp/cp-tree.h
> > @@ -424,6 +424,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
> > DECL_FINAL_P (in FUNCTION_DECL)
> > QUALIFIED_NAME_IS_TEMPLATE (in SCOPE_REF)
> > DECLTYPE_FOR_INIT_CAPTURE (in DECLTYPE_TYPE)
> > + CONSTRUCTOR_IS_DEPENDENT (in CONSTRUCTOR)
> > TINFO_USED_TEMPLATE_ID (in TEMPLATE_INFO)
> > PACK_EXPANSION_SIZEOF_P (in *_PACK_EXPANSION)
> > OVL_USING_P (in OVERLOAD)
> > @@ -4202,6 +4203,11 @@ more_aggr_init_expr_args_p (const
> > aggr_init_expr_arg_iterator *iter)
> > B b{1,2}, not B b({1,2}) or B b = {1,2}. */
> > #define CONSTRUCTOR_IS_DIRECT_INIT(NODE) (TREE_LANG_FLAG_0
> > (CONSTRUCTOR_CHECK (NODE)))
> > +/* True if this CONSTRUCTOR is instantiation-dependent and needs to be
> > + substituted. */
> > +#define CONSTRUCTOR_IS_DEPENDENT(NODE) \
> > + (TREE_LANG_FLAG_1 (CONSTRUCTOR_CHECK (NODE)))
> > +
> > /* True if this CONSTRUCTOR should not be used as a variable initializer
> > because it was loaded from a constexpr variable with mutable fields.
> > */
> > #define CONSTRUCTOR_MUTABLE_POISON(NODE) \
> > diff --git gcc/cp/pt.c gcc/cp/pt.c
> > index e4f76478f54..ae77bae6b29 100644
> > --- gcc/cp/pt.c
> > +++ gcc/cp/pt.c
> > @@ -25800,6 +25800,11 @@ instantiation_dependent_r (tree *tp, int
> > *walk_subtrees,
> > return *tp;
> > break;
> > + case CONSTRUCTOR:
> > + if (CONSTRUCTOR_IS_DEPENDENT (*tp))
> > + return *tp;
> > + break;
> > +
> > default:
> > break;
> > }
> > diff --git gcc/cp/semantics.c gcc/cp/semantics.c
> > index e654750d249..4ff09ad3fb7 100644
> > --- gcc/cp/semantics.c
> > +++ gcc/cp/semantics.c
> > @@ -2795,11 +2795,14 @@ finish_compound_literal (tree type, tree
> > compound_literal,
> > return error_mark_node;
> > }
> > - if (processing_template_decl)
> > + if (instantiation_dependent_expression_p (compound_literal)
> > + || dependent_type_p (type))
> > {
> > TREE_TYPE (compound_literal) = type;
> > /* Mark the expression as a compound literal. */
> > TREE_HAS_CONSTRUCTOR (compound_literal) = 1;
> > + /* And as instantiation-dependent. */
> > + CONSTRUCTOR_IS_DEPENDENT (compound_literal) = true;
> > if (fcl_context == fcl_c99)
> > CONSTRUCTOR_C99_COMPOUND_LITERAL (compound_literal) = 1;
> > return compound_literal;
> > @@ -2822,8 +2825,7 @@ finish_compound_literal (tree type, tree
> > compound_literal,
> > && check_array_initializer (NULL_TREE, type, compound_literal))
> > return error_mark_node;
> > compound_literal = reshape_init (type, compound_literal, complain);
> > - if (SCALAR_TYPE_P (type)
> > - && !BRACE_ENCLOSED_INITIALIZER_P (compound_literal)
> > + if (!BRACE_ENCLOSED_INITIALIZER_P (compound_literal)
> > && !check_narrowing (type, compound_literal, complain))
> > return error_mark_node;
>
> Hmm, I wonder why we would want to call check_narrowing here at all; we
> ought to get the narrowing warning from the normal conversion process.
> Perhaps the issue is that we need to pass LOOKUP_NO_NARROWING to
> digest_init.
reshape_init never ends up calling convert_for_assignment or convert_like_real,
so even if we signalled to check narrowing to it, it wouldn't help.
reshape_init calls check_narrowing just for enum initialization.
Marek
