From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21651 invoked by alias); 27 Jan 2019 00:22:31 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 21641 invoked by uid 89); 27 Jan 2019 00:22:31 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-1.4 required=5.0 tests=BAYES_00,KAM_NUMSUBJECT,RCVD_IN_DNSWL_NONE autolearn=no version=3.3.2 spammy=Wed X-HELO: mail-ot1-f48.google.com Received: from mail-ot1-f48.google.com (HELO mail-ot1-f48.google.com) (209.85.210.48) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Sun, 27 Jan 2019 00:22:30 +0000 Received: by mail-ot1-f48.google.com with SMTP id e12so11817511otl.5 for ; Sat, 26 Jan 2019 16:22:29 -0800 (PST) MIME-Version: 1.0 References: <20190117190921.GM19569@redhat.com> <4958169a-e8c8-4ca0-6f99-ce360b4834d5@redhat.com> <20190118141207.GN19569@redhat.com> <20190122211021.GC26714@redhat.com> <33c9ff91-1aff-d328-7349-767b196eaecf@redhat.com> <20190123175735.GF26714@redhat.com> <20190125001757.GH26714@redhat.com> <26ab4b9a-c572-7a9f-7fcd-18bcdc7e3c1d@redhat.com> <20190125212043.GN26714@redhat.com> In-Reply-To: <20190125212043.GN26714@redhat.com> From: Jason Merrill Date: Sun, 27 Jan 2019 00:25:00 -0000 Message-ID: Subject: Re: C++ PATCH for c++/78244 - narrowing conversion in template not detected, part 2 To: Marek Polacek Cc: GCC Patches Content-Type: text/plain; charset="UTF-8" X-IsSubscribed: yes X-SW-Source: 2019-01/txt/msg01559.txt.bz2 On Fri, Jan 25, 2019 at 4:20 PM Marek Polacek 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 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