From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 82788 invoked by alias); 25 Jan 2019 00:17:59 -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 82766 invoked by uid 89); 25 Jan 2019 00:17:58 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-0.4 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,KAM_NUMSUBJECT,SPF_HELO_PASS autolearn=no version=3.3.2 spammy= 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; Fri, 25 Jan 2019 00:17:57 +0000 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 77CC6A7875 for ; Fri, 25 Jan 2019 00:17:56 +0000 (UTC) Received: from redhat.com (ovpn-125-95.rdu2.redhat.com [10.10.125.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E400B60BE0; Fri, 25 Jan 2019 00:17:55 +0000 (UTC) Date: Fri, 25 Jan 2019 00:51:00 -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: <20190125001757.GH26714@redhat.com> 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> 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/msg01481.txt.bz2 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? Marek