From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 102222 invoked by alias); 27 Jan 2019 20:14:31 -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 102212 invoked by uid 89); 27 Jan 2019 20:14:31 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-1.4 required=5.0 tests=BAYES_00,KAM_NUMSUBJECT,SPF_HELO_PASS autolearn=no version=3.3.2 spammy=reviews X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Sun, 27 Jan 2019 20:14:29 +0000 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 560AA58E51 for ; Sun, 27 Jan 2019 20:14:28 +0000 (UTC) Received: from redhat.com (ovpn-120-67.rdu2.redhat.com [10.10.120.67]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A957C102BCEB; Sun, 27 Jan 2019 20:14:26 +0000 (UTC) Date: Sun, 27 Jan 2019 20:18:00 -0000 From: Marek Polacek To: Jason Merrill Cc: GCC Patches Subject: Re: C++ PATCH for c++/78244 - narrowing conversion in template not detected, part 2 Message-ID: <20190127201428.GR26714@redhat.com> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-SW-Source: 2019-01/txt/msg01572.txt.bz2 On Sat, Jan 26, 2019 at 07:22:17PM -0500, Jason Merrill wrote: > 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? I think I should keep poking at it, but I welcome any advice. But perhaps we should leave this for GCC 10? I'll add the new test to the PR. > > - 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. No difference (I ran the testsuite with some additional checking). > OK with or without this hunk. Thanks for the reviews. Marek