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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id t10-20020a37460a000000b0074e17456a87sm9942169qka.7.2023.05.02.12.53.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 May 2023 12:53:32 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Tue, 2 May 2023 15:53:31 -0400 (EDT) To: Patrick Palka cc: Jason Merrill , gcc-patches@gcc.gnu.org Subject: Re: [PATCH 1/2] c++: potentiality of templated memfn call [PR109480] In-Reply-To: <2aea65a6-eef7-d171-8790-bbb5b9c45d8a@idea> Message-ID: <3744435a-11ea-f9bf-c8de-b040e98b3c0b@idea> References: <20230501195902.1915703-1-ppalka@redhat.com> <6da23365-02cd-8ac1-2fdc-91b284af6a68@redhat.com> <2aea65a6-eef7-d171-8790-bbb5b9c45d8a@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=-13.9 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,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 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: 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; > > > > >