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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id i12-20020a37c20c000000b0069fc13ce20asm3648125qkm.59.2022.06.02.13.30.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Jun 2022 13:30:59 -0700 (PDT) Message-ID: <7b8d13d3-cdab-a749-287a-8770e7f00d41@redhat.com> Date: Thu, 2 Jun 2022 16:30:58 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH] c++: cv-quals of dummy obj for non-dep memfn call [PR105637] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org References: <20220526183450.2331967-1-ppalka@redhat.com> <527705e5-b69c-f1bd-f531-6bb43e10713b@idea> <34d2cabf-523c-098d-633d-8e3d7619f8b1@redhat.com> <1874d5e6-8a87-2b90-d9a2-95be5831af16@idea> <0fcce048-5e2c-4071-43e3-20f9fb72ba52@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=-13.9 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, 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 X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 02 Jun 2022 20:31:08 -0000 On 6/2/22 15:57, Patrick Palka wrote: > On Thu, 2 Jun 2022, Jason Merrill wrote: > >> On 5/27/22 09:57, Patrick Palka wrote: >>> On Thu, 26 May 2022, Patrick Palka wrote: >>> >>>> On Thu, 26 May 2022, Jason Merrill wrote: >>>> >>>>> On 5/26/22 14:57, Patrick Palka wrote: >>>>>> On Thu, 26 May 2022, Patrick Palka wrote: >>>>>> >>>>>>> Here we expect the calls to BaseClass::baseDevice resolve to the >>>>>>> second, >>>>>>> third and fourth overloads respectively in light of the >>>>>>> cv-qualifiers >>>>>>> of 'this' in each case. But ever since r12-6075-g2decd2cabe5a4f, >>>>>>> the >>>>>>> calls incorrectly resolve to the first overload at instantiation >>>>>>> time. >>>>>>> >>>>>>> This happens because the calls to BaseClass::baseDevice are all >>>>>>> deemed >>>>>>> non-dependent (ever since r7-755-g23cb72663051cd made us ignore the >>>>>>> dependentness of 'this' when considering the dependence of a >>>>>>> non-static >>>>>>> memfn call), hence we end up checking the call ahead of time, using >>>>>>> as >>>>>>> the object argument a dummy object of type BaseClass. Since this >>>>>>> object >>>>>>> argument is cv-unqualified, the calls incoherently resolve to the >>>>>>> first >>>>>>> overload of baseDevice. Before r12-6075, this incorrect result >>>>>>> would >>>>>>> just get silently discarded and we'd end up redoing OR at >>>>>>> instantiation >>>>>>> time using 'this' as the object argument. But after r12-6075, we >>>>>>> now >>>>>>> reuse this incorrect result at instantiation time. >>>>>>> >>>>>>> This patch fixes this by making finish_call_expr request from >>>>>>> maybe_dummy_object a cv-qualified object consistent with the >>>>>>> cv-quals of >>>>>>> 'this'. That way, ahead of time OR using a dummy object will give >>>>>>> us >>>>>>> the right answer and we could safely reuse it at instantiation time. >>>>>>> >>>>>>> NB: r7-755 is also the cause of the related issue PR105742. Not >>>>>>> sure >>>>>>> if there's a fix that could resolve both PRs at once.. >>>>>>> >>>>>>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK >>>>>>> for trunk/12? >>>>>>> >>>>>>> PR c++/105637 >>>>>>> >>>>>>> gcc/cp/ChangeLog: >>>>>>> >>>>>>> * semantics.cc (finish_call_expr): Pass a cv-qualified object >>>>>>> type to maybe_dummy_object that is consistent with the >>>>>>> cv-qualifiers of 'this' if available. >>>>>>> >>>>>>> gcc/testsuite/ChangeLog: >>>>>>> >>>>>>> * g++.dg/template/non-dependent23.C: New test. >>>>>>> --- >>>>>>> gcc/cp/semantics.cc | 15 ++++++++--- >>>>>>> .../g++.dg/template/non-dependent23.C | 25 >>>>>>> +++++++++++++++++++ >>>>>>> 2 files changed, 37 insertions(+), 3 deletions(-) >>>>>>> create mode 100644 >>>>>>> gcc/testsuite/g++.dg/template/non-dependent23.C >>>>>>> >>>>>>> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc >>>>>>> index cd7a2818feb..1d9348c6cf1 100644 >>>>>>> --- a/gcc/cp/semantics.cc >>>>>>> +++ b/gcc/cp/semantics.cc >>>>>>> @@ -2802,16 +2802,25 @@ finish_call_expr (tree fn, vec >>>>>>> **args, bool disallow_virtual, >>>>>>> [class.access.base] says that we need to convert 'this' to B* >>>>>>> as >>>>>>> part of the access, so we pass 'B' to maybe_dummy_object. */ >>>>>>> + tree object_type = BINFO_TYPE (BASELINK_ACCESS_BINFO >>>>>>> (fn)); >>>>>>> if (DECL_MAYBE_IN_CHARGE_CONSTRUCTOR_P (get_first_fn (fn))) >>>>>>> { >>>>>>> /* A constructor call always uses a dummy object. (This >>>>>>> constructor >>>>>>> call which has the form A::A () is actually invalid and >>>>>>> we are >>>>>>> going to reject it later in build_new_method_call.) */ >>>>>>> - object = build_dummy_object (BINFO_TYPE >>>>>>> (BASELINK_ACCESS_BINFO >>>>>>> (fn))); >>>>>>> + object = build_dummy_object (object_type); >>>>>>> } >>>>>>> else >>>>>>> - object = maybe_dummy_object (BINFO_TYPE (BASELINK_ACCESS_BINFO >>>>>>> (fn)), >>>>>>> - NULL); >>>>>>> + { >>>>>>> + if (current_class_ref) >>>>>>> + { >>>>>>> + /* Make sure that if maybe_dummy_object gives us a dummy >>>>>>> object, >>>>>>> + it'll have the same cv-quals as '*this'. */ >>>>>>> + int quals = cp_type_quals (TREE_TYPE >>>>>>> (current_class_ref)); >>>>>>> + object_type = cp_build_qualified_type (object_type, >>>>>>> quals); >>>>>>> + } >>>>>>> + object = maybe_dummy_object (object_type, NULL); >>>>>>> + } >>>>>>> result = build_new_method_call (object, fn, args, >>>>>>> NULL_TREE, >>>>>>> (disallow_virtual >>>>>> >>>>>> Drat, this fix doesn't interact well with 'this'-capturing lambdas: >>>>>> >>>>>> struct BaseClass { >>>>>> void baseDevice(); // #1 >>>>>> void baseDevice() const = delete; // #2 >>>>>> }; >>>>>> >>>>>> template >>>>>> struct TopClass : T { >>>>>> void failsToCompile() { >>>>>> [this] { BaseClass::baseDevice(); }(); >>>>>> } >>>>>> }; >>>>>> >>>>>> template struct TopClass; >>>>>> >>>>>> Here after the fix, we'd incorrectly select the const #2 overload at >>>>>> template definition time because current_class_ref is the const 'this' >>>>>> for the lambda rather than the non-const 'this' for TopClass.. I >>>>>> suppose >>>>>> we need something like current_nonlambda_class_type for getting at the >>>>>> innermost non-lambda 'this'? >>>>> >>>>> Do you want maybe_resolve_dummy (ob, false)? >>>> >>>> That sadly doesn't seem to work -- the object type is BaseClass which is >>>> not necessarily a base of the dependent TopClass, so >>>> resolvable_dummy_lambda returns NULL_TREE. I guess it would work at >>>> instantiation time though. >>> >>> Ah, what seems to work well is directly using lambda_expr_this_capture >>> instead of maybe_resolve_dummy. And we might as well handle this in >>> maybe_dummy_object for benefit of all callers. How does the following >>> look? Smoke tested with RUNTESTFLAGS="dg.exp=*.C", full bootstrap and >>> regtesting in progress. >>> >>> -- >8 -- >>> >>> Subject: [PATCH] c++: cv-quals of dummy obj for non-dep memfn call >>> [PR105637] >>> >>> In non-dependent23.C below we expect the BaseClass::baseDevice calls to >>> resolve to the second, third and fourth overloads respectively in light >>> of the cv-qualifiers of 'this' in each case. But ever since >>> r12-6075-g2decd2cabe5a4f, the calls incorrectly resolve to the first >>> overload at instantiation time. >>> >>> This happens because the calls to BaseClass::baseDevice are all deemed >>> non-dependent (ever since r7-755-g23cb72663051cd made us ignore 'this' >>> dependence when considering the dependence of a non-static memfn call), >>> hence we end up checking the call ahead of time, using as the object >>> argument a dummy object of type BaseClass. Since this object argument >>> is cv-unqualified, the calls incoherently resolve to the first overload >>> of baseDevice. Before r12-6075, this incorrect result would just get >>> silently discarded and we'd end up redoing OR at instantiation time >>> using 'this' as the object argument. But after r12-6075, we now reuse >>> this incorrect result at instantiation time. >>> >>> This patch fixes this by making maybe_dummy_object respect the cv-quals >>> of (the non-lambda) 'this' when returning a dummy object. Thus, ahead >>> of time OR using a dummy object will give us the right answer that is >>> consistent with the instantiation time answer. >>> >>> An earlier version of this patch didn't handle 'this'-capturing lambdas >>> correctly, which caused us to mishandle lambda-this22.C below. >>> >>> PR c++/105637 >>> >>> gcc/cp/ChangeLog: >>> >>> * tree.cc (maybe_dummy_object): When returning a dummy >>> object, respect the cv-quals of 'this' if available. >>> >>> gcc/testsuite/ChangeLog: >>> >>> * g++.dg/cpp0x/lambda/lambda-this22.C: New test. >>> * g++.dg/template/non-dependent23.C: New test. >>> --- >>> gcc/cp/tree.cc | 19 +++++++++++++- >>> .../g++.dg/cpp0x/lambda/lambda-this22.C | 20 +++++++++++++++ >>> .../g++.dg/template/non-dependent23.C | 25 +++++++++++++++++++ >>> 3 files changed, 63 insertions(+), 1 deletion(-) >>> create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C >>> create mode 100644 gcc/testsuite/g++.dg/template/non-dependent23.C >>> >>> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc >>> index 09162795801..679bf05b721 100644 >>> --- a/gcc/cp/tree.cc >>> +++ b/gcc/cp/tree.cc >>> @@ -4330,7 +4330,24 @@ maybe_dummy_object (tree type, tree* binfop) >>> (TREE_TYPE (current_class_ref), context))) >>> decl = current_class_ref; >>> else >>> - decl = build_dummy_object (context); >>> + { >>> + /* Return a dummy object whose cv-quals are consistent with (the >>> + non-lambda) 'this' if available. */ >>> + if (current_class_ref) >>> + { >>> + int quals = 0; >>> + if (current == current_class_type) >>> + quals = cp_type_quals (TREE_TYPE (current_class_ref)); >>> + else if (lambda_function (current_class_type)) >>> + { >>> + tree lambda = CLASSTYPE_LAMBDA_EXPR (current_class_type); >> >> How about >> >> else if (tree lambda = CLASSTYPE_LAMBDA_EXPR (current_class_type)) >> >> ? OK with that change. > > Unfortunately the lambda_function test is necessary to avoid crashing > on lambda-ice11.C; the test mirrors what resolvable_dummy_lambda does > ever since r207999 / r208028 to avoid the crash. Hmm, how about adjusting lambda_expr_this_capture to avoid the crash? >>> + if (tree cap = lambda_expr_this_capture (lambda, false)) >>> + quals = cp_type_quals (TREE_TYPE (TREE_TYPE (cap))); >>> + } >>> + context = cp_build_qualified_type (context, quals); >>> + } >>> + decl = build_dummy_object (context); >>> + } >>> return decl; >>> } >>> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C >>> b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C >>> new file mode 100644 >>> index 00000000000..c9e512b1621 >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C >>> @@ -0,0 +1,20 @@ >>> +// PR c++/105637 >>> +// { dg-do compile { target c++11 } } >>> + >>> +struct BaseClass { >>> + void baseDevice(); // #1 >>> + void baseDevice() const = delete; // #2 >>> +}; >>> + >>> +template >>> +struct TopClass : T { >>> + void failsToCompile() { >>> + [this] { BaseClass::baseDevice(); }(); // should select #2, not #1 >>> + } >>> + >>> + void failsToCompile() const { >>> + [this] { BaseClass::baseDevice(); }(); // { dg-error "deleted" } >>> + } >>> +}; >>> + >>> +template struct TopClass; >>> diff --git a/gcc/testsuite/g++.dg/template/non-dependent23.C >>> b/gcc/testsuite/g++.dg/template/non-dependent23.C >>> new file mode 100644 >>> index 00000000000..ef95c591b75 >>> --- /dev/null >>> +++ b/gcc/testsuite/g++.dg/template/non-dependent23.C >>> @@ -0,0 +1,25 @@ >>> +// PR c++/105637 >>> + >>> +struct BaseClass { >>> + void baseDevice(); // #1 >>> + void baseDevice() const; // #2 >>> + void baseDevice() volatile; // #3 >>> + void baseDevice() const volatile; // #4 >>> +}; >>> + >>> +template >>> +struct TopClass : T { >>> + void failsToCompile() const { >>> + BaseClass::baseDevice(); // should select #2, not #1 >>> + } >>> + >>> + void failsToCompile() volatile { >>> + BaseClass::baseDevice(); // should select #3, not #1 >>> + } >>> + >>> + void failsToCompile() const volatile { >>> + BaseClass::baseDevice(); // should select #4, not #1 >>> + } >>> +}; >>> + >>> +template struct TopClass; >> >> >