On Fri, Jan 25, 2019 at 4:20 PM Marek Polacek <pola...@redhat.com> wrote: > On Fri, Jan 25, 2019 at 10:05:00AM -0500, Jason Merrill wrote: > > On 1/24/19 7:17 PM, Marek Polacek wrote: > > > 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? > > > > That patch still needs a test for the aggregate case. > > Ok, this is a version with Wnarrowing16.C added. > > ...but we still don't warn for the TYPE_NON_AGGREGATE_CLASS case in > finish_compound_literal, so the nightmare continues.
Alas. Are you going to keep looking at that, or would you like me to take over? > - 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; Does this hunk actually make a difference? It looks like check_narrowing only does anything for arithmetic types. OK with or without this hunk. Jason