On Wed, Jan 23, 2019 at 03:34:04PM -0500, Jason Merrill wrote:
> On Wed, Jan 23, 2019 at 12:57 PM Marek Polacek <pola...@redhat.com> wrote:
> >
> > On Wed, Jan 23, 2019 at 09:00:36AM -0500, Jason Merrill wrote:
> > > I was talking about digest_init, not reshape_init. digest_init calls
> > > convert_for_initialization.
> >
> > /facepalm
> >
> > So yes, digest_init calls convert_for_initialization which will end up
> > calling perform_implicit_conversion_flags which could call convert_like_real
> > where the narrowing warnings are given, but it doesn't, we go to this case:
> >
> > else if (processing_template_decl && conv->kind != ck_identity)
> > {
> > /* In a template, we are only concerned about determining the
> > type of non-dependent expressions, so we do not have to
> > perform the actual conversion. But for initializers, we
> > need to be able to perform it at instantiation
> > (or instantiate_non_dependent_expr) time. */
> > expr = build1 (IMPLICIT_CONV_EXPR, type, expr);
> >
> > finish_decltype_type throws away the expression because it's not dependent,
> > and
> > only uses its type. So narrowing remains undetected. Not sure if I should
> > mess
> > with perform_implicit_conversion_flags.
>
> Let's try that; this is a situation where the comment is incorrect.
> Perhaps just call check_narrowing here if appropriate, rather than go
> through the whole conversion machinery.
I have not been successful.
First, I modified perform_implicit_conversion_flags to go the convert_like
route when dealing with something non-dependent. That breaks e.g. in
build_value_init:
346 /* The AGGR_INIT_EXPR tweaking below breaks in templates. */
347 gcc_assert (!processing_template_decl
348 || (SCALAR_TYPE_P (type) || TREE_CODE (type) == ARRAY_TYPE));
Even if I restrict the convert_like way for non-dependent exprs in a template
for scalars, it still breaks elsewhere, e.g. constexpr-template3.C where it
complains about taking the address of an rvalue.
Second, I added check_narrowing to the processing_template_decl case in
perform_implicit_conversion_flags. That works except it breaks
constexpr-inst1.C -- we no longer get the error. That's because currently
check_narrowing in finish_compound_literal calls maybe_constant_init, which
calls instantiate_constexpr_fns and we get the desired diagnostic. But if
I move check_narrowing to perform_implicit_conversion_flags, we no longer
call it in this case -- processing_template_decl is 0 so we call convert_like
but that doesn't do the trick.
So, back to the patch that leaves check_narrowing in finish_compound_literal?
Marek
