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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id i4-20020a05622a08c400b002fac21ffd71sm2621758qte.6.2022.05.27.06.57.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 May 2022 06:57:36 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Fri, 27 May 2022 09:57:36 -0400 (EDT) To: Patrick Palka cc: Jason Merrill , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: cv-quals of dummy obj for non-dep memfn call [PR105637] In-Reply-To: <1874d5e6-8a87-2b90-d9a2-95be5831af16@idea> Message-ID: 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> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-14.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, 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, 27 May 2022 13:57:44 -0000 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); + 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; -- 2.36.1.195.g8ddf593a25 > > > > > > > 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; > > > > -- > > > > 2.36.1.182.g6afdb07b7b > > > > > > > > > > > > > > > >