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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id m10-20020ae9e70a000000b0060ded8d915csm2968540qka.29.2022.03.04.14.34.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Mar 2022 14:34:32 -0800 (PST) Message-ID: Date: Fri, 4 Mar 2022 17:34:30 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH] c++: detecting copy-init context during CTAD [PR102137] To: Patrick Palka , gcc-patches@gcc.gnu.org References: <20220304182436.122498-1-ppalka@redhat.com> From: Jason Merrill In-Reply-To: <20220304182436.122498-1-ppalka@redhat.com> 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=-13.1 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_LOW, RCVD_IN_MSPIKE_H5, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) 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, 04 Mar 2022 22:34:43 -0000 On 3/4/22 14:24, Patrick Palka wrote: > Here we're failing to communicate to cp_finish_decl from tsubst_expr > that we're in a copy-initialization context (via the LOOKUP_ONLYCONVERTING > flag), which causes do_class_deduction to always consider explicit > deduction guides when performing CTAD for a templated variable initializer. > > We could fix this by passing LOOKUP_ONLYCONVERTING appropriately when > calling cp_finish_decl from tsubst_expr, but it seems do_class_deduction > can determine if we're in a copy-init context by simply inspecting the > initializer, and thus render its flags parameter unnecessary, which is > what this patch implements. (If we were to fix this in tsubst_expr > instead, I think we'd have to inspect the initializer in the same way > in order to detect a copy-init context?) Hmm, does this affect conversions as well? Looks like it does: struct A { explicit operator int(); }; template void f() { T t = A(); } int main() { f(); // wrongly accepted } The reverse, initializing via an explicit constructor, is caught by code in build_aggr_init much like the code your patch adds to do_auto_deduction; perhaps we should move/copy that code to cp_finish_decl? > Bootstrapped and regtestd on x86_64-pc-linux-gnu, does this look OK for > trunk? > > PR c++/102137 > > gcc/cp/ChangeLog: > > * cp-tree.h (do_auto_deduction): Remove flags parameter. > * decl.cc (cp_finish_decl): Adjust call to do_auto_deduction. > * pt.cc (convert_template_argument): Likewise. > (do_class_deduction): Remove flags parameter and instead > determine if we're in a copy-init context by inspecting the > initializer. > (do_auto_deduction): Adjust call to do_class_deduction. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp1z/class-deduction108.C: New test. > --- > gcc/cp/cp-tree.h | 3 +- > gcc/cp/decl.cc | 2 +- > gcc/cp/pt.cc | 23 +++++++------ > .../g++.dg/cpp1z/class-deduction108.C | 32 +++++++++++++++++++ > 4 files changed, 48 insertions(+), 12 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction108.C > > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h > index ac723901098..c2ef6544389 100644 > --- a/gcc/cp/cp-tree.h > +++ b/gcc/cp/cp-tree.h > @@ -7279,8 +7279,7 @@ extern tree do_auto_deduction (tree, tree, tree, > = tf_warning_or_error, > auto_deduction_context > = adc_unspecified, > - tree = NULL_TREE, > - int = LOOKUP_NORMAL); > + tree = NULL_TREE); > extern tree type_uses_auto (tree); > extern tree type_uses_auto_or_concept (tree); > extern void append_type_to_template_for_access_check (tree, tree, tree, > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc > index 199ac768d43..152f657e9f2 100644 > --- a/gcc/cp/decl.cc > +++ b/gcc/cp/decl.cc > @@ -8039,7 +8039,7 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p, > outer_targs = DECL_TI_ARGS (decl); > type = TREE_TYPE (decl) = do_auto_deduction (type, d_init, auto_node, > tf_warning_or_error, adc, > - outer_targs, flags); > + outer_targs); > if (type == error_mark_node) > return; > if (TREE_CODE (type) == FUNCTION_TYPE) > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > index d94d4538faa..66fc8cacdc6 100644 > --- a/gcc/cp/pt.cc > +++ b/gcc/cp/pt.cc > @@ -8567,8 +8567,7 @@ convert_template_argument (tree parm, > can happen in the context of -fnew-ttp-matching. */; > else if (tree a = type_uses_auto (t)) > { > - t = do_auto_deduction (t, arg, a, complain, adc_unify, args, > - LOOKUP_IMPLICIT); > + t = do_auto_deduction (t, arg, a, complain, adc_unify, args); > if (t == error_mark_node) > return error_mark_node; > } > @@ -29832,8 +29831,7 @@ ctad_template_p (tree tmpl) > type. */ > > static tree > -do_class_deduction (tree ptype, tree tmpl, tree init, > - int flags, tsubst_flags_t complain) > +do_class_deduction (tree ptype, tree tmpl, tree init, tsubst_flags_t complain) > { > /* We should have handled this in the caller. */ > if (DECL_TEMPLATE_TEMPLATE_PARM_P (tmpl)) > @@ -29881,6 +29879,13 @@ do_class_deduction (tree ptype, tree tmpl, tree init, > if (type_dependent_expression_p (init)) > return ptype; > > + bool copy_init_p = true; > + if (!init > + || TREE_CODE (init) == TREE_LIST > + || (BRACE_ENCLOSED_INITIALIZER_P (init) > + && CONSTRUCTOR_IS_DIRECT_INIT (init))) > + copy_init_p = false; > + > tree type = TREE_TYPE (tmpl); > > bool try_list_ctor = false; > @@ -29929,7 +29934,7 @@ do_class_deduction (tree ptype, tree tmpl, tree init, > /* Prune explicit deduction guides in copy-initialization context (but > not copy-list-initialization). */ > bool elided = false; > - if (!list_init_p && (flags & LOOKUP_ONLYCONVERTING)) > + if (!list_init_p && copy_init_p) > { > for (lkp_iterator iter (cands); !elided && iter; ++iter) > if (DECL_NONCONVERTING_P (STRIP_TEMPLATE (*iter))) > @@ -30007,7 +30012,7 @@ do_class_deduction (tree ptype, tree tmpl, tree init, > } > /* [over.match.list]/1: In copy-list-initialization, if an explicit > constructor is chosen, the initialization is ill-formed. */ > - else if (flags & LOOKUP_ONLYCONVERTING) > + else if (copy_init_p) > { > if (DECL_NONCONVERTING_P (fndecl)) > { > @@ -30045,7 +30050,7 @@ do_class_deduction (tree ptype, tree tmpl, tree init, > /* Replace occurrences of 'auto' in TYPE with the appropriate type deduced > from INIT. AUTO_NODE is the TEMPLATE_TYPE_PARM used for 'auto' in TYPE. > The CONTEXT determines the context in which auto deduction is performed > - and is used to control error diagnostics. FLAGS are the LOOKUP_* flags. > + and is used to control error diagnostics. > > OUTER_TARGS is used during template argument deduction (context == adc_unify) > to properly substitute the result. It's also used in the adc_unify and > @@ -30058,7 +30063,7 @@ do_class_deduction (tree ptype, tree tmpl, tree init, > tree > do_auto_deduction (tree type, tree init, tree auto_node, > tsubst_flags_t complain, auto_deduction_context context, > - tree outer_targs, int flags) > + tree outer_targs) > { > if (init == error_mark_node) > return error_mark_node; > @@ -30079,7 +30084,7 @@ do_auto_deduction (tree type, tree init, tree auto_node, > > if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node)) > /* C++17 class template argument deduction. */ > - return do_class_deduction (type, tmpl, init, flags, complain); > + return do_class_deduction (type, tmpl, init, complain); > > if (init == NULL_TREE || TREE_TYPE (init) == NULL_TREE) > /* Nothing we can do with this, even in deduction context. */ > diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction108.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction108.C > new file mode 100644 > index 00000000000..f76671c287a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction108.C > @@ -0,0 +1,32 @@ > +// PR c++/102137 > +// { dg-do compile { target c++17 } } > + > +template > +struct A { > + A(); > + A(int); > +}; > + > +explicit A(int) -> A; > +explicit A() -> A; > + > +template class T> > +void f() { > + T x1 = 0; // { dg-error "deduction|no match" } > + T x2 = {0}; // { dg-error "explicit deduction guide" } > + T x3(0); > + T x4{0}; > + T x5; > +} > + > +template > +void g(T t) { > + A a1 = t; // { dg-error "deduction|no match" } > + A a2 = {t}; // { dg-error "explicit deduction guide" } > + A a3(t); > + A a4{t}; > + A a5; > +} > + > +template void f(); > +template void g(int);