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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id b11-20020ac87fcb000000b002f39b99f671sm3681061qtk.11.2022.06.02.12.53.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Jun 2022 12:53:45 -0700 (PDT) Message-ID: <5cdbdb4b-09d2-f86c-63b8-7d1c44021c1d@redhat.com> Date: Thu, 2 Jun 2022 15:53:44 -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++: don't substitute TEMPLATE_PARM_CONSTRAINT [PR100374] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org References: <20220527180543.2908762-1-ppalka@redhat.com> <89dc1f48-0c65-a4e7-8791-3d541e074bb7@redhat.com> <9366f773-368b-2957-c3ff-0fb8d17c240d@idea> <1fe00521-20fb-5673-7a00-1d3dc28def56@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: 8bit 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, 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: Thu, 02 Jun 2022 19:53:52 -0000 On 6/2/22 11:40, Patrick Palka wrote: > On Tue, 31 May 2022, Jason Merrill wrote: > >> On 5/31/22 08:56, Patrick Palka wrote: >>> On Sun, 29 May 2022, Jason Merrill wrote: >>> >>>> On 5/29/22 22:10, Jason Merrill wrote: >>>>> On 5/27/22 14:05, Patrick Palka wrote: >>>>>> This makes us avoid substituting into the TEMPLATE_PARM_CONSTRAINT of >>>>>> each template parameter except as necessary for (friend) declaration >>>>>> matching, like we already do for the overall >>>>>> TEMPLATE_PARMS_CONSTRAINTS >>>>>> of a template parameter list. >>>>>> >>>>>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK >>>>>> for >>>>>> trunk and perhaps 12.2?  Also tested on range-v3 and cmcstl2. >>>>> >>>>> Are there already tests that cover the friend cases? >>> >>> Yes, by cpp2a/concepts-friend{2,3,7}.C I think. >>> >>>> >>>> Also, don't you also need to handle specialization of partial >>>> instantiations? >>> >>> Hmm, do you have an example? IIUC we call tsubst_friend_function and >>> tsubst_friend_class only from instantiate_class_template_1, which always >>> uses the most general template and full template argument set to >>> instantiate any friend declarations. So friend declarations are never >>> partially instantiated I think. (And IIUC non-friends are irrelevant >>> here since we don't ever want to substitute their constraints outside of >>> satisfaction.) >> >> From C++20 CA104: >> >> template struct A { >> template U f(U) requires C; >> template U f(U) requires C; >> }; >> >> // Substitute int for T in above requirements to find match. >> template <> template U A::f(U) requires C { } > > Aha, thanks. In this case of declaration matching, it looks like > determine_specialization ignores all but the trailing requirement > clause. I think it's doable if a little messy to precisely handle > this case but in the meantime it seems we could get 90% of the way there > by considering the overall constraints instead of just the trailing > constraints? Something like the following. > > (Either way, IIUC the tsubst_template_parm change shouldn't affect this > case at all since determine_specialization uses comp_template_parms > instead of template_heads_equivalent_p and so it ignores > TEMPLATE_PARM_CONSTRAINT.) OK. > -- >8 -- > > Subject: [PATCH] c++: don't substitute TEMPLATE_PARM_CONSTRAINT [PR100374] > > This makes us avoid substituting into the TEMPLATE_PARM_CONSTRAINT of > each template parameter except as necessary for friend declaration > matching, like we already do for the overall associated constraints. > > In passing this improves upon the CA104 implementation of explicit > specialization mathing of a constrained function template inside > a class template, by considering the overall constraints instead of > just the trailing constraints. This allows us to correctly handle the > first three explicit specializations in concepts-spec2.C below, but > because we compare the constraints as a whole, it means we incorrectly > accept the fourth explicit specialization. For complete correctness, > we should be using tsubst_each_template_parm_constraint and > template_parameter_heads_equivalent_p in determine_specialization. > > PR c++/100374 > > gcc/cp/ChangeLog: > > * pt.cc (determine_specialization): Compare overall constraints, > not just the trailing constraints, in the CA104 case. > (tsubst_each_template_parm_constraint): Define. > (tsubst_friend_function): Use it. > (tsubst_friend_class): Use it. > (tsubst_template_parm): Don't substitute TEMPLATE_PARM_CONSTRAINT. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp2a/concepts-template-parm11.C: New test. > --- > gcc/cp/pt.cc | 41 +++++++++++++++---- > gcc/testsuite/g++.dg/cpp2a/concepts-spec2.C | 15 +++++++ > .../g++.dg/cpp2a/concepts-template-parm11.C | 20 +++++++++ > 3 files changed, 69 insertions(+), 7 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-spec2.C > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-template-parm11.C > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > index 45dd036c2d5..d867ce8e141 100644 > --- a/gcc/cp/pt.cc > +++ b/gcc/cp/pt.cc > @@ -184,6 +184,7 @@ static int unify_pack_expansion (tree, tree, tree, > tree, unification_kind_t, bool, bool); > static tree copy_template_args (tree); > static tree tsubst_template_parms (tree, tree, tsubst_flags_t); > +static void tsubst_each_template_parm_constraint (tree, tree, tsubst_flags_t); > tree most_specialized_partial_spec (tree, tsubst_flags_t); > static tree tsubst_aggr_type (tree, tree, tsubst_flags_t, tree, int); > static tree tsubst_arg_types (tree, tree, tree, tsubst_flags_t, tree); > @@ -2323,8 +2324,8 @@ determine_specialization (tree template_id, > if (!compparms (fn_arg_types, decl_arg_types)) > continue; > > - tree freq = get_trailing_function_requirements (fn); > - tree dreq = get_trailing_function_requirements (decl); > + tree freq = get_constraints (fn); > + tree dreq = get_constraints (decl); > if (!freq != !dreq) > continue; > if (freq) > @@ -2333,7 +2334,7 @@ determine_specialization (tree template_id, > constraint-expression. */ > tree fargs = DECL_TI_ARGS (fn); > tsubst_flags_t complain = tf_none; > - freq = tsubst_constraint (freq, fargs, complain, fn); > + freq = tsubst_constraint_info (freq, fargs, complain, fn); > if (!cp_tree_equal (freq, dreq)) > continue; > } > @@ -11235,7 +11236,12 @@ tsubst_friend_function (tree decl, tree args) > tree parms = DECL_TEMPLATE_PARMS (new_friend); > tree treqs = TEMPLATE_PARMS_CONSTRAINTS (parms); > treqs = maybe_substitute_reqs_for (treqs, new_friend); > - TEMPLATE_PARMS_CONSTRAINTS (parms) = treqs; > + if (treqs != TEMPLATE_PARMS_CONSTRAINTS (parms)) > + { > + TEMPLATE_PARMS_CONSTRAINTS (parms) = treqs; > + /* As well as each TEMPLATE_PARM_CONSTRAINT. */ > + tsubst_each_template_parm_constraint (parms, args, tf_warning_or_error); > + } > } > > /* The mangled name for the NEW_FRIEND is incorrect. The function > @@ -11481,6 +11487,8 @@ tsubst_friend_class (tree friend_tmpl, tree args) > { > tree parms = tsubst_template_parms (DECL_TEMPLATE_PARMS (friend_tmpl), > args, tf_warning_or_error); > + tsubst_each_template_parm_constraint (parms, args, > + tf_warning_or_error); > location_t saved_input_location = input_location; > input_location = DECL_SOURCE_LOCATION (friend_tmpl); > tree cons = get_constraints (tmpl); > @@ -11515,6 +11523,8 @@ tsubst_friend_class (tree friend_tmpl, tree args) > DECL_FRIEND_CONTEXT (friend_tmpl)); > --processing_template_decl; > set_constraints (tmpl, ci); > + tsubst_each_template_parm_constraint (DECL_TEMPLATE_PARMS (tmpl), > + args, tf_warning_or_error); > } > > /* Inject this template into the enclosing namspace scope. */ > @@ -13627,7 +13637,6 @@ tsubst_template_parm (tree t, tree args, tsubst_flags_t complain) > > default_value = TREE_PURPOSE (t); > parm_decl = TREE_VALUE (t); > - tree constraint = TEMPLATE_PARM_CONSTRAINTS (t); > > parm_decl = tsubst (parm_decl, args, complain, NULL_TREE); > if (TREE_CODE (parm_decl) == PARM_DECL > @@ -13635,13 +13644,31 @@ tsubst_template_parm (tree t, tree args, tsubst_flags_t complain) > parm_decl = error_mark_node; > default_value = tsubst_template_arg (default_value, args, > complain, NULL_TREE); > - constraint = tsubst_constraint (constraint, args, complain, NULL_TREE); > > tree r = build_tree_list (default_value, parm_decl); > - TEMPLATE_PARM_CONSTRAINTS (r) = constraint; > + TEMPLATE_PARM_CONSTRAINTS (r) = TEMPLATE_PARM_CONSTRAINTS (t); > return r; > } > > +/* Substitute in-place the TEMPLATE_PARM_CONSTRAINT of each template > + parameter in PARMS for sake of declaration matching. */ > + > +static void > +tsubst_each_template_parm_constraint (tree parms, tree args, > + tsubst_flags_t complain) > +{ > + ++processing_template_decl; > + for (; parms; parms = TREE_CHAIN (parms)) > + { > + tree level = TREE_VALUE (parms); > + for (tree parm : tree_vec_range (level)) > + TEMPLATE_PARM_CONSTRAINTS (parm) > + = tsubst_constraint (TEMPLATE_PARM_CONSTRAINTS (parm), args, > + complain, NULL_TREE); > + } > + --processing_template_decl; > +} > + > /* Substitute the ARGS into the indicated aggregate (or enumeration) > type T. If T is not an aggregate or enumeration type, it is > handled as if by tsubst. IN_DECL is as for tsubst. If > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-spec2.C b/gcc/testsuite/g++.dg/cpp2a/concepts-spec2.C > new file mode 100644 > index 00000000000..e95a5c10c9c > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-spec2.C > @@ -0,0 +1,15 @@ > +// { dg-do compile { target c++20 } } > + > +template concept C = true; > + > +template struct A { > + template U> void f(); > + template U> void f(); > + template U> void f(); > +}; > + > +constexpr int n = sizeof(int); > +template<> template U> void A::f() { } > +template<> template U> void A::f() { } > +template<> template U> void A::f() { } // { dg-error "match" } > +template<> template void A::f() requires C { } // { dg-error "match" "" { xfail *-*-* } } > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-template-parm11.C b/gcc/testsuite/g++.dg/cpp2a/concepts-template-parm11.C > new file mode 100644 > index 00000000000..498e3c175cf > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-template-parm11.C > @@ -0,0 +1,20 @@ > +// PR c++/100374 > +// { dg-do compile { target c++20 } } > + > +template > +concept C = requires { typename T; }; > + > +template > +struct A { > + template U> > + void f(); > + > + template U> > + struct B; > +}; > + > +int main() { > + A a; > + a.f(); > + using type = A::B; > +}