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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id i7-20020a0cab47000000b0063c71b62239sm1451472qvb.42.2023.07.21.10.44.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Jul 2023 10:44:52 -0700 (PDT) Message-ID: Date: Fri, 21 Jul 2023 13:44:51 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] c++: fix ICE with is_really_empty_class [PR110106] To: Marek Polacek Cc: Patrick Palka , GCC Patches References: <20230718211458.858343-1-polacek@redhat.com> <7007162f-c356-cbde-575e-1cbbd545323d@idea> <03d798a6-0951-1d11-5ae4-476e85f5636e@redhat.com> From: Jason Merrill In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TRACKER_ID,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 7/20/23 15:51, Marek Polacek wrote: > On Thu, Jul 20, 2023 at 02:37:07PM -0400, Jason Merrill wrote: >> On 7/20/23 14:13, Marek Polacek wrote: >>> On Wed, Jul 19, 2023 at 10:11:27AM -0400, Patrick Palka wrote: >>>> On Tue, 18 Jul 2023, Marek Polacek via Gcc-patches wrote: >>>> >>>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk and branches? >>>> >>>> Looks reasonable to me. >>> >>> Thanks. >>>> Though I wonder if we could also fix this by not checking potentiality >>>> at all in this case? The problematic call to is_rvalue_constant_expression >>>> happens from cp_parser_constant_expression with 'allow_non_constant' != 0 >>>> and with 'non_constant_p' being a dummy out argument that comes from >>>> cp_parser_functional_cast, so the result of is_rvalue_constant_expression >>>> is effectively unused in this case, and we should be able to safely elide >>>> it when 'allow_non_constant && non_constant_p == nullptr'. >>> >>> Sounds plausible. I think my patch could be applied first since it >>> removes a tiny bit of code, then I can hopefully remove the flag below, >>> then maybe go back and optimize the call to is_rvalue_constant_expression. >>> Does that sound sensible? >>> >>>> Relatedly, ISTM the member cp_parser::non_integral_constant_expression_p >>>> is also effectively unused and could be removed? >>> >>> It looks that way. Seems it's only used in cp_parser_constant_expression: >>> 10806 if (allow_non_constant_p) >>> 10807 *non_constant_p = parser->non_integral_constant_expression_p; >>> but that could be easily replaced by a local var. I'd be happy to see if >>> we can actually do away with it. (I wonder why it was introduced and when >>> it actually stopped being useful.) >> >> It was for the C++98 notion of constant-expression, which was more of a >> parser-level notion, and has been supplanted by the C++11 version. I'm >> happy to remove it, and therefore remove the is_rvalue_constant_expression >> call. > > Wonderful. I'll do that next. > >>>>> -- >8 -- >>>>> >>>>> is_really_empty_class is liable to crash when it gets an incomplete >>>>> or dependent type. Since r11-557, we pass the yet-uninstantiated >>>>> class type S<0> of the PARM_DECL s to is_really_empty_class -- because >>>>> of the potential_rvalue_constant_expression -> is_rvalue_constant_expression >>>>> change in cp_parser_constant_expression. Here we're not parsing >>>>> a template so we did not check COMPLETE_TYPE_P as we should. >>>>> >>>>> PR c++/110106 >>>>> >>>>> gcc/cp/ChangeLog: >>>>> >>>>> * constexpr.cc (potential_constant_expression_1): Check COMPLETE_TYPE_P >>>>> even when !processing_template_decl. >>>>> >>>>> gcc/testsuite/ChangeLog: >>>>> >>>>> * g++.dg/cpp0x/noexcept80.C: New test. >>>>> --- >>>>> gcc/cp/constexpr.cc | 2 +- >>>>> gcc/testsuite/g++.dg/cpp0x/noexcept80.C | 12 ++++++++++++ >>>>> 2 files changed, 13 insertions(+), 1 deletion(-) >>>>> create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept80.C >>>>> >>>>> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc >>>>> index 6e8f1c2b61e..1f59c5472fb 100644 >>>>> --- a/gcc/cp/constexpr.cc >>>>> +++ b/gcc/cp/constexpr.cc >>>>> @@ -9116,7 +9116,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, >>>>> if (now && want_rval) >>>>> { >>>>> tree type = TREE_TYPE (t); >>>>> - if ((processing_template_decl && !COMPLETE_TYPE_P (type)) >>>>> + if (!COMPLETE_TYPE_P (type) >>>>> || dependent_type_p (type) >> >> There shouldn't be a problem completing the type here, so it seems to me >> that we're missing a call to complete_type_p, at least when >> !processing_template_decl. Probably need to move the dependent_type_p check >> up as a result. > > Like so? > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? OK. > -- >8 -- > is_really_empty_class is liable to crash when it gets an incomplete > or dependent type. Since r11-557, we pass the yet-uninstantiated > class type S<0> of the PARM_DECL s to is_really_empty_class -- because > of the potential_rvalue_constant_expression -> is_rvalue_constant_expression > change in cp_parser_constant_expression. Here we're not parsing > a template so we did not check COMPLETE_TYPE_P as we should. > > It should work to complete the type before checking COMPLETE_TYPE_P. > > PR c++/110106 > > gcc/cp/ChangeLog: > > * constexpr.cc (potential_constant_expression_1): Try to complete the > type when !processing_template_decl. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/noexcept80.C: New test. > --- > gcc/cp/constexpr.cc | 5 +++-- > gcc/testsuite/g++.dg/cpp0x/noexcept80.C | 12 ++++++++++++ > 2 files changed, 15 insertions(+), 2 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept80.C > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > index 6e8f1c2b61e..fb94f3cefcb 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -9116,8 +9116,9 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, > if (now && want_rval) > { > tree type = TREE_TYPE (t); > - if ((processing_template_decl && !COMPLETE_TYPE_P (type)) > - || dependent_type_p (type) > + if (dependent_type_p (type) > + || !COMPLETE_TYPE_P (processing_template_decl > + ? type : complete_type (type)) > || is_really_empty_class (type, /*ignore_vptr*/false)) > /* An empty class has no data to read. */ > return true; > diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept80.C b/gcc/testsuite/g++.dg/cpp0x/noexcept80.C > new file mode 100644 > index 00000000000..3e90af747e2 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept80.C > @@ -0,0 +1,12 @@ > +// PR c++/110106 > +// { dg-do compile { target c++11 } } > + > +template struct S > +{ > +}; > + > +struct G { > + G(S<0>); > +}; > + > +void y(S<0> s) noexcept(noexcept(G{s})); > > base-commit: 4b8878fbf7b74ea5c3405c9f558df0517036f131