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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id bs14-20020a05620a470e00b006b58d8f6181sm6339747qkb.72.2022.09.16.08.05.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Sep 2022 08:05:49 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Fri, 16 Sep 2022 11:05:48 -0400 (EDT) To: Patrick Palka cc: Jason Merrill , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: constraint matching, TEMPLATE_ID_EXPR, current inst In-Reply-To: <8abd55bf-7f1e-5ab5-895e-a3f42631ec56@idea> Message-ID: <568de6fa-810c-2b6e-63c7-0d2f208cc8c0@idea> References: <20220915155822.4021344-1-ppalka@redhat.com> <549844d1-be60-592b-5e2b-1e4071f6a7f8@redhat.com> <8abd55bf-7f1e-5ab5-895e-a3f42631ec56@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_LOW,SPF_HELO_NONE,SPF_NONE,TXREP 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 Fri, 16 Sep 2022, Patrick Palka wrote: > On Fri, 16 Sep 2022, Jason Merrill wrote: > > > On 9/15/22 11:58, Patrick Palka wrote: > > > Here we're crashing during constraint matching for the instantiated > > > hidden friends due to two issues with dependent substitution into a > > > TEMPLATE_ID_EXPR naming a template from the current instantiation > > > (as performed from maybe_substitute_reqs_for for C<3> with T=T): > > > > > > * tsubst_copy substitutes into such a TEMPLATE_DECL by looking it > > > up from the substituted class scope. But for this to not fail when > > > the args are dependent, we need to pass entering_scope=true for the > > > class scope substitution so that we obtain the primary template type > > > A (which has TYPE_BINFO) instead of the implicit instantiation > > > A (which doesn't). > > > * lookup_and_finish_template_variable shouldn't instantiate a > > > TEMPLATE_ID_EXPR that names a TEMPLATE_DECL which has more than > > > one level of (unsubstituted) parameters (such as A::C). > > > > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > > > trunk? > > > > > > gcc/cp/ChangeLog: > > > > > > * pt.cc (lookup_and_finish_template_variable): Don't > > > instantiate if the template's scope is dependent. > > > (tsubst_copy) : Pass entering_scope=true > > > when substituting the class scope. > > > > > > gcc/testsuite/ChangeLog: > > > > > > * g++.dg/cpp2a/concepts-friend10.C: New test. > > > --- > > > gcc/cp/pt.cc | 14 +++++++------ > > > .../g++.dg/cpp2a/concepts-friend10.C | 21 +++++++++++++++++++ > > > 2 files changed, 29 insertions(+), 6 deletions(-) > > > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend10.C > > > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > > > index db4e808adec..bfcbe0b8670 100644 > > > --- a/gcc/cp/pt.cc > > > +++ b/gcc/cp/pt.cc > > > @@ -10475,14 +10475,15 @@ tree > > > lookup_and_finish_template_variable (tree templ, tree targs, > > > tsubst_flags_t complain) > > > { > > > - templ = lookup_template_variable (templ, targs); > > > - if (!any_dependent_template_arguments_p (targs)) > > > + tree var = lookup_template_variable (templ, targs); > > > + if (TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (templ)) == 1 > > > + && !any_dependent_template_arguments_p (targs)) > > > > I notice that finish_id_expression_1 uses the equivalent of > > type_dependent_expression_p (var). Does that work here? > > Hmm, it does, but kind of by accident: type_dependent_expression_p > returns true for all variable TEMPLATE_ID_EXPRs because of their empty > TREE_TYPE (as set by finish_template_variable). ... as set by lookup_template_variable, rather > So testing t_d_e_p here > is equivalent to testing processing_template_decl, it seems -- maximally > conservative. > > We can improve type_dependent_expression_p for variable TEMPLATE_ID_EXPR > by ignoring its (always empty) TREE_TYPE and just considering dependence > of its template and args directly. > > Doing so exposes that value_dependent_expression_p is wrong for > (non-type-dependent) variable template specializations -- since we don't > set/track DECL_DEPENDENT_INIT_P for them, the VAR_DECL branch ends up > returning false even if the initializer depends on outer args. Instead, > I suppose we can give a reasonably conservative answer by considering > dependence of its enclosing scope as we do for FUNCTION_DECL. > > Does the following seem reasonable? Bootstrapped and regtested on > x86_64-pc-linux-gnu. > > -- >8 -- > > gcc/cp/ChangeLog: > > * pt.cc (finish_template_variable): Consider only the innermost > template parms since we have only the innermost args. > (lookup_and_finish_template_variable): Check > type_dependent_expression_p instead. > (tsubst_copy) : Pass entering_scope=true > when substituting the class scope. > (value_dependent_expression_p) : Move below ... > : ... here. Fall through for variable template > specializations. > (type_dependent_expression_p): Handle variable TEMPLATE_ID_EXPR > precisely. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp1y/noexcept1.C: Expect another ahead of time error. > * g++.dg/cpp1y/var-templ70.C: New test. > * g++.dg/cpp2a/concepts-friend10.C: New test. > --- > gcc/cp/pt.cc | 53 ++++++++++++------- > gcc/testsuite/g++.dg/cpp1y/noexcept1.C | 2 +- > gcc/testsuite/g++.dg/cpp1y/var-templ70.C | 22 ++++++++ > .../g++.dg/cpp2a/concepts-friend10.C | 24 +++++++++ > 4 files changed, 82 insertions(+), 19 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ70.C > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend10.C > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > index db4e808adec..88a09891a00 100644 > --- a/gcc/cp/pt.cc > +++ b/gcc/cp/pt.cc > @@ -10447,10 +10447,10 @@ finish_template_variable (tree var, tsubst_flags_t complain) > tree templ = TREE_OPERAND (var, 0); > tree arglist = TREE_OPERAND (var, 1); > > - tree parms = DECL_TEMPLATE_PARMS (templ); > - arglist = coerce_innermost_template_parms (parms, arglist, templ, complain, > - /*req_all*/true, > - /*use_default*/true); > + tree parms = DECL_INNERMOST_TEMPLATE_PARMS (templ); > + arglist = coerce_template_parms (parms, arglist, templ, complain, > + /*req_all*/true, > + /*use_default*/true); > if (arglist == error_mark_node) > return error_mark_node; > > @@ -10475,14 +10475,14 @@ tree > lookup_and_finish_template_variable (tree templ, tree targs, > tsubst_flags_t complain) > { > - templ = lookup_template_variable (templ, targs); > - if (!any_dependent_template_arguments_p (targs)) > + tree var = lookup_template_variable (templ, targs); > + if (!type_dependent_expression_p (var)) > { > - templ = finish_template_variable (templ, complain); > - mark_used (templ); > + var = finish_template_variable (var, complain); > + mark_used (var); > } > > - return convert_from_reference (templ); > + return convert_from_reference (var); > } > > /* If the set of template parameters PARMS contains a template parameter > @@ -17282,7 +17282,8 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl) > TEMPLATE_DECL with `D' as its DECL_CONTEXT. Now we > have to substitute this with one having context `D'. */ > > - tree context = tsubst (DECL_CONTEXT (t), args, complain, in_decl); > + tree context = tsubst_aggr_type (DECL_CONTEXT (t), args, complain, > + in_decl, /*entering_scope=*/true); > return lookup_field (context, DECL_NAME(t), 0, false); > } > else > @@ -27684,13 +27685,6 @@ value_dependent_expression_p (tree expression) > /* A dependent member function of the current instantiation. */ > return dependent_type_p (BINFO_TYPE (BASELINK_BINFO (expression))); > > - case FUNCTION_DECL: > - /* A dependent member function of the current instantiation. */ > - if (DECL_CLASS_SCOPE_P (expression) > - && dependent_type_p (DECL_CONTEXT (expression))) > - return true; > - break; > - > case IDENTIFIER_NODE: > /* A name that has not been looked up -- must be dependent. */ > return true; > @@ -27725,7 +27719,19 @@ value_dependent_expression_p (tree expression) > && value_expr == error_mark_node)) > return true; > } > - return false; > + if (!variable_template_specialization_p (expression)) > + /* For variable template specializations, also consider dependence > + of the enclosing scope. For other specializations it seems we > + can trust DECL_DEPENDENT_INIT_P. */ > + return false; > + /* Fall through. */ > + > + case FUNCTION_DECL: > + /* A dependent member of the current instantiation. */ > + if (DECL_CLASS_SCOPE_P (expression) > + && dependent_type_p (DECL_CONTEXT (expression))) > + return true; > + break; > > case DYNAMIC_CAST_EXPR: > case STATIC_CAST_EXPR: > @@ -28095,6 +28101,17 @@ type_dependent_expression_p (tree expression) > expression = BASELINK_FUNCTIONS (expression); > } > > + /* A variable TEMPLATE_ID_EXPR is type-dependent iff the template or > + arguments are. */ > + if (TREE_CODE (expression) == TEMPLATE_ID_EXPR) > + { > + tree tmpl = TREE_OPERAND (expression, 0); > + tree args = TREE_OPERAND (expression, 1); > + if (variable_template_p (tmpl) && !variable_concept_p (tmpl)) > + return type_dependent_expression_p (tmpl) > + || any_dependent_template_arguments_p (args); > + } > + > /* A function or variable template-id is type-dependent if it has any > dependent template arguments. */ > if (VAR_OR_FUNCTION_DECL_P (expression) > diff --git a/gcc/testsuite/g++.dg/cpp1y/noexcept1.C b/gcc/testsuite/g++.dg/cpp1y/noexcept1.C > index 86e46c96148..a660b9d6c9e 100644 > --- a/gcc/testsuite/g++.dg/cpp1y/noexcept1.C > +++ b/gcc/testsuite/g++.dg/cpp1y/noexcept1.C > @@ -8,6 +8,6 @@ struct C { > template friend int foo() noexcept(b<1>); // { dg-error "not usable in a constant expression|different exception specifier" } > }; > > -template int foo() noexcept(b<1>); > +template int foo() noexcept(b<1>); // { dg-error "not usable in a constant expression" } > > auto a = C(); > diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ70.C b/gcc/testsuite/g++.dg/cpp1y/var-templ70.C > new file mode 100644 > index 00000000000..e1040165c34 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ70.C > @@ -0,0 +1,22 @@ > +// Verify we correctly compute value dependence for variable template > +// specializations. > +// { dg-do compile { target c++17 } } > + > +template static constexpr int value = false; > + > +template > +void f() { > + // value is not dependent, so we can check this ahead of time. > + static_assert(value, ""); // { dg-error "assertion failed" } > +} > + > +template > +struct A { > + template static constexpr bool member = T(); > + auto f() { > + // member is not type dependent, but we consider it value dependent > + // since it's a member of the current instantiation, so we don't check > + // this ahead of time. > + static_assert(member, ""); > + } > +}; > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend10.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend10.C > new file mode 100644 > index 00000000000..bb5e1e6038b > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend10.C > @@ -0,0 +1,24 @@ > +// Verify we don't crash during constraint matching containing a > +// TEMPLATE_ID_EXPR that names a template from the current instantiation. > +// { dg-do compile { target c++20 } } > + > +template static constexpr bool False = false; > + > +template > +struct A { > + template static constexpr bool C = sizeof(T) > N; > + friend constexpr void f(A) requires C<1> { } > + friend constexpr void f(A) requires C<1> && False { } > +}; > + > +template > +struct A { > + template static constexpr bool C = sizeof(T) > N; > + friend constexpr void g(A) requires C<1> { } > + friend constexpr void g(A) requires C<1> && False { } > +}; > + > +int main() { > + f(A{}); > + g(A{}); > +} > -- > 2.38.0.rc0 > >