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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id w138-20020a376290000000b0069fd9de088esm1590601qkb.93.2022.05.26.11.57.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 May 2022 11:57:45 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Thu, 26 May 2022 14:57:44 -0400 (EDT) To: Patrick Palka cc: gcc-patches@gcc.gnu.org, jason@redhat.com Subject: Re: [PATCH] c++: cv-quals of dummy obj for non-dep memfn call [PR105637] In-Reply-To: <20220526183450.2331967-1-ppalka@redhat.com> Message-ID: <527705e5-b69c-f1bd-f531-6bb43e10713b@idea> References: <20220526183450.2331967-1-ppalka@redhat.com> 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=-14.4 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: Thu, 26 May 2022 18:57:49 -0000 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'? > 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 > >