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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id ee5-20020a05620a800500b0074df1d74841sm10957006qkb.72.2023.05.03.12.55.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 May 2023 12:55:21 -0700 (PDT) Message-ID: <8dacd562-3441-872f-ab4f-20015694eb8f@redhat.com> Date: Wed, 3 May 2023 15:55:20 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org References: <20230501195902.1915703-1-ppalka@redhat.com> <6da23365-02cd-8ac1-2fdc-91b284af6a68@redhat.com> <2aea65a6-eef7-d171-8790-bbb5b9c45d8a@idea> <3744435a-11ea-f9bf-c8de-b040e98b3c0b@idea> From: Jason Merrill In-Reply-To: <3744435a-11ea-f9bf-c8de-b040e98b3c0b@idea> 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=-15.0 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_H2,SPF_HELO_NONE,SPF_NONE,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 5/2/23 15:53, Patrick Palka wrote: > on Tue, 2 May 2023, Patrick Palka wrote: > >> On Tue, 2 May 2023, Jason Merrill wrote: >> >>> On 5/1/23 15:59, Patrick Palka wrote: >>>> Here we're incorrectly deeming the templated call a.g() inside b's >>>> initializer as potentially constant, despite g being non-constexpr, >>>> which leads to us wastefully instantiating the initializer ahead of time >>>> and triggering a bug in access checking deferral (which will get fixed >>>> in the subsequent patch). >>>> >>>> This patch fixes this by calling get_fns earlier during potentiality >>>> checking so that we also handle the templated form of a member function >>>> call (whose overall callee is a COMPONENT_REF) when checking if the called >>>> function is constexpr etc. >>>> >>>> PR c++/109480 >>>> >>>> gcc/cp/ChangeLog: >>>> >>>> * constexpr.cc (potential_constant_expression_1) : >>>> Reorganize to call get_fns sooner. Remove dead store to 'fun'. >>>> >>>> gcc/testsuite/ChangeLog: >>>> >>>> * g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the >>>> expected "without object" diagnostic isn't replaced by a >>>> "call to non-constexpr function" diagnostic. >>>> * g++.dg/template/non-dependent25.C: New test. >>>> --- >>>> gcc/cp/constexpr.cc | 16 ++++++++-------- >>>> gcc/testsuite/g++.dg/cpp0x/noexcept59.C | 2 +- >>>> gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++ >>>> 3 files changed, 23 insertions(+), 9 deletions(-) >>>> create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C >>>> >>>> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc >>>> index d1097764b10..29d872d0a5e 100644 >>>> --- a/gcc/cp/constexpr.cc >>>> +++ b/gcc/cp/constexpr.cc >>>> @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool >>>> want_rval, bool strict, bool now, >>>> if (fun && is_overloaded_fn (fun)) >>>> { >>>> + if (!RECUR (fun, true)) >>>> + return false; >>>> + fun = get_fns (fun); >>>> + >>>> if (TREE_CODE (fun) == FUNCTION_DECL) >>>> { >>>> if (builtin_valid_in_constant_expr_p (fun)) >>>> @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool >>>> want_rval, bool strict, bool now, >>>> expression the address will be folded away, so look >>>> through it now. */ >>>> if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun) >>>> - && !DECL_CONSTRUCTOR_P (fun)) >>>> + && !DECL_CONSTRUCTOR_P (fun) >>>> + && !processing_template_decl) >>> >>> I don't see any rationale for this hunk? >> >> Now that we call get_fns earlier, we can reach this code path with a >> templated non-static memfn call, but the code that follows assumes >> non-templated form. >> >> I tried teaching it to handle the templated form too, but there's >> apparently two different templated forms for non-static memfn calls, >> one with a COMPONENT_REF callee and one with an ordinary BASELINK >> callee (without a implicit object argument). In the former the implict >> object argument is inside the COMPONENT_REF (and is a reference instead >> of a pointer), and in the latter we don't even have an implicit object >> argument to inspect. >> >> FWIW I think which form we use depends on whether we know if the called >> function is a member of the current instantiation, e.g >> >> struct A { void f(); }; >> >> template struct B; >> >> template >> struct C : B { >> void g(); >> >> void h() { >> A::f(); // templated form has BASELINK callee, no object arg >> C::g(); // templated form has COMPONENT_REF callee >> } >> }; >> >> So it seemed best to punt on templated non-static memfn calls here for >> now and treat that as a separate enhancement. > > And I'm not even sure if the code path in question is necessary at all > anymore: disabling it outright doesn't cause any regressions in the testsuite. > It seems effectively equivalent to the body of the loop over the args a few > lines later: If removing that hunk doesn't regress anything, let's do it. Probably that should have happened in r13-55-ge9d2adc17d0dbe > for (; i < nargs; ++i) > { > tree x = get_nth_callarg (t, i); > /* In a template, reference arguments haven't been converted to > REFERENCE_TYPE and we might not even know if the parameter > is a reference, so accept lvalue constants too. */ > bool rv = processing_template_decl ? any : rval; > /* Don't require an immediately constant value, as constexpr > substitution might not use the value of the argument. */ > bool sub_now = false; > if (!potential_constant_expression_1 (x, rv, strict, > sub_now, fundef_p, flags, > jump_target)) > return false; > } > >> >>> >>>> { >>>> tree x = get_nth_callarg (t, 0); >>>> if (is_this_parameter (x)) >>>> @@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool >>>> want_rval, bool strict, bool now, >>>> i = 1; >>>> } >>>> } >>>> - else >>>> - { >>>> - if (!RECUR (fun, true)) >>>> - return false; >>>> - fun = get_first_fn (fun); >>>> - } >>>> + >>>> + fun = OVL_FIRST (fun); >>>> /* Skip initial arguments to base constructors. */ >>>> if (DECL_BASE_CONSTRUCTOR_P (fun)) >>>> i = num_artificial_parms_for (fun); >>>> - fun = DECL_ORIGIN (fun); >>>> } >>>> else if (fun) >>>> { >>>> diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C >>>> b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C >>>> index c752601ba09..1dc826d3111 100644 >>>> --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C >>>> +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C >>>> @@ -3,7 +3,7 @@ >>>> template class A >>>> { >>>> - void e (); >>>> + constexpr bool e () { return true; }; >>>> bool f (int() noexcept(this->e())); // { dg-error "this" } >>>> bool g (int() noexcept(e())); // { dg-error "without object" } >>>> }; >>>> diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C >>>> b/gcc/testsuite/g++.dg/template/non-dependent25.C >>>> new file mode 100644 >>>> index 00000000000..a2f9801e11f >>>> --- /dev/null >>>> +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C >>>> @@ -0,0 +1,14 @@ >>>> +// PR c++/109480 >>>> + >>>> +template >>>> +struct A { >>>> + void f() { >>>> + A a; >>>> + const bool b = a.g(); >>>> + } >>>> + >>>> +private: >>>> + bool g() const; >>>> +}; >>>> + >>>> +template struct A; >>> >>> >> >