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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id n206-20020a3740d7000000b006a65c58db99sm5196693qka.64.2022.06.03.07.53.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Jun 2022 07:53:11 -0700 (PDT) Message-ID: Date: Fri, 3 Jun 2022 10:53:10 -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> <7b8d13d3-cdab-a749-287a-8770e7f00d41@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=-13.3 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: Fri, 03 Jun 2022 14:53:18 -0000 On 6/3/22 10:46, Patrick Palka wrote: > On Thu, 2 Jun 2022, Jason Merrill wrote: > >> 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>>>>>>>> va_gc> >>>>>>>>> **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? > > I'm afraid I'm not sure how to do that :/ In particular for the case > where add_capture_p is nonzero and the given lambda lacks a > lambda_function. I suppose we can relax the assert in the !add_capture_p > case but that seems somewhat hacky. > > I noticed that finish_this_expr, another user of lambda_expr_this_capture, > isn't guarded by resolvable_dummy_lambda. I believe it gets away with > this because it checks lambda-ness of TREE_TYPE (current_class_ref) instead > of current_class_type. Perhaps we should do the same in maybe_dummy_object? > This avoids the ICE in lambda-ice11.C without needing to check lambda_function, > and seems like a cleaner approach overall. > > -- >8 -- > > Subject: [PATCH] c++: cv-quals of dummy obj for non-dep memfn call [PR105637] > > 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 | 31 ++++++++++++++----- > .../g++.dg/cpp0x/lambda/lambda-this22.C | 20 ++++++++++++ > .../g++.dg/template/non-dependent23.C | 25 +++++++++++++++ > 3 files changed, 69 insertions(+), 7 deletions(-) > 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 2b9cb7e1c7b..183febffb5d 100644 > --- a/gcc/cp/tree.cc > +++ b/gcc/cp/tree.cc > @@ -4319,15 +4319,32 @@ maybe_dummy_object (tree type, tree* binfop) > if (binfop) > *binfop = binfo; > > - if (current_class_ref > - /* current_class_ref might not correspond to current_class_type if > - we're in tsubst_default_argument or a lambda-declarator; in either > - case, we want to use current_class_ref if it matches CONTEXT. */ > - && (same_type_ignoring_top_level_qualifiers_p > - (TREE_TYPE (current_class_ref), context))) > + /* current_class_ref might not correspond to current_class_type if > + we're in tsubst_default_argument or a lambda-declarator; in either > + case, we want to use current_class_ref if it matches CONTEXT. */ > + tree ctype = current_class_ref ? TREE_TYPE (current_class_ref) : NULL_TREE; > + if (ctype > + && same_type_ignoring_top_level_qualifiers_p (ctype, 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 (ctype) > + { > + int quals = 0; > + if (LAMBDA_TYPE_P (ctype)) > + { > + tree lambda = CLASSTYPE_LAMBDA_EXPR (ctype); And just checking CLASSTYPE_LAMBDA_EXPR (ctype) still isn't enough? > + if (tree cap = lambda_expr_this_capture (lambda, false)) > + quals = cp_type_quals (TREE_TYPE (TREE_TYPE (cap))); > + } > + else > + quals = cp_type_quals (ctype); > + 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;