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[130.44.159.43]) by smtp.gmail.com with ESMTPSA id r1-20020ac87941000000b003e1f984c9f3sm11697450qtt.93.2023.03.29.14.36.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Mar 2023 14:36:15 -0700 (PDT) Message-ID: Date: Wed, 29 Mar 2023 17:36:13 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH 1/2] c++: improve "NTTP argument considered unused" fix [PR53164, PR105848] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org References: <20230323211803.396326-1-ppalka@redhat.com> <4a04306f-faa9-5dd8-c850-05aa4a21d36e@idea> From: Jason Merrill In-Reply-To: <4a04306f-faa9-5dd8-c850-05aa4a21d36e@idea> 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=-12.6 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,RCVD_IN_MSPIKE_H2,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 3/27/23 09:30, Patrick Palka wrote: > On Thu, 23 Mar 2023, Patrick Palka wrote: > >> r13-995-g733a792a2b2e16 worked around the problem of FUNCTION_DECL >> template arguments not always getting marked as odr-used by redundantly >> calling mark_used on the substituted ADDR_EXPR callee of a CALL_EXPR. >> This is just a narrow workaround however, since using a FUNCTION_DECL as >> a template argument alone should constitutes an odr-use; we shouldn't >> need to subsequently e.g. call the function or take its address. Agreed. But why didn't we already wrap it in an ADDR_EXPR? Even for reference tparms convert_nontype_argument should do that. >> This patch fixes this in a more general way at template specialization >> time by walking the template arguments of the specialization and calling >> mark_used on all entities used within. As before, the call to mark_used >> as it worst a no-op, but it compensates for the situation where we end up >> forming a specialization from a template context in which mark_used is >> inhibited. Another approach would be to call mark_used whenever we >> substitute a TEMPLATE_PARM_INDEX, but that would result in many more >> redundant calls to mark_used compared to this approach. >> >> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for >> trunk? >> >> PR c++/53164 >> PR c++/105848 >> >> gcc/cp/ChangeLog: >> >> * pt.cc (instantiate_class_template): Call >> mark_template_arguments_used. >> (tsubst_copy_and_build) : Revert r13-995 change. >> (mark_template_arguments_used): Define. >> (instantiate_template): Call mark_template_arguments_used. >> >> gcc/testsuite/ChangeLog: >> >> * g++.dg/template/fn-ptr3a.C: New test. >> * g++.dg/template/fn-ptr4.C: New test. >> --- >> gcc/cp/pt.cc | 51 ++++++++++++++++-------- >> gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 ++++++++++++ >> gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 +++++++ >> 3 files changed, 74 insertions(+), 16 deletions(-) >> create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C >> create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr4.C >> >> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc >> index 7e4a8de0c8b..9b3cc33331c 100644 >> --- a/gcc/cp/pt.cc >> +++ b/gcc/cp/pt.cc >> @@ -220,6 +220,7 @@ static tree make_argument_pack (tree); >> static tree enclosing_instantiation_of (tree tctx); >> static void instantiate_body (tree pattern, tree args, tree d, bool nested); >> static tree maybe_dependent_member_ref (tree, tree, tsubst_flags_t, tree); >> +static void mark_template_arguments_used (tree); >> >> /* Make the current scope suitable for access checking when we are >> processing T. T can be FUNCTION_DECL for instantiated function >> @@ -12142,6 +12143,9 @@ instantiate_class_template (tree type) >> cp_unevaluated_operand = 0; >> c_inhibit_evaluation_warnings = 0; >> } >> + >> + mark_template_arguments_used (INNERMOST_TEMPLATE_ARGS (args)); >> + >> /* Use #pragma pack from the template context. */ >> saved_maximum_field_alignment = maximum_field_alignment; >> maximum_field_alignment = TYPE_PRECISION (pattern); >> @@ -21173,22 +21177,10 @@ tsubst_copy_and_build (tree t, >> } >> >> /* Remember that there was a reference to this entity. */ >> - if (function != NULL_TREE) >> - { >> - tree inner = function; >> - if (TREE_CODE (inner) == ADDR_EXPR >> - && TREE_CODE (TREE_OPERAND (inner, 0)) == FUNCTION_DECL) >> - /* We should already have called mark_used when taking the >> - address of this function, but do so again anyway to make >> - sure it's odr-used: at worst this is a no-op, but if we >> - obtained this FUNCTION_DECL as part of ahead-of-time overload >> - resolution then that call to mark_used wouldn't have marked it >> - odr-used yet (53164). */ >> - inner = TREE_OPERAND (inner, 0); >> - if (DECL_P (inner) >> - && !mark_used (inner, complain) && !(complain & tf_error)) >> - RETURN (error_mark_node); >> - } >> + if (function != NULL_TREE >> + && DECL_P (function) >> + && !mark_used (function, complain) && !(complain & tf_error)) >> + RETURN (error_mark_node); >> >> if (!maybe_fold_fn_template_args (function, complain)) >> return error_mark_node; >> @@ -21883,6 +21875,31 @@ check_instantiated_args (tree tmpl, tree args, tsubst_flags_t complain) >> return result; >> } >> >> +/* Call mark_used on each entity within the template arguments ARGS of some >> + template specialization, to ensure that each such entity is considered >> + odr-used regardless of whether the specialization was first formed in a >> + template context. >> + >> + This function assumes push_to_top_level has been called beforehand, and >> + that processing_template_decl has been set iff the template arguments >> + are dependent. */ >> + >> +static void >> +mark_template_arguments_used (tree args) >> +{ >> + gcc_checking_assert (TMPL_ARGS_DEPTH (args) == 1); >> + >> + if (processing_template_decl) >> + return; >> + >> + auto mark_used_r = [](tree *tp, int *, void *) { >> + if (DECL_P (*tp)) >> + mark_used (*tp, tf_none); >> + return NULL_TREE; >> + }; >> + cp_walk_tree_without_duplicates (&args, mark_used_r, nullptr); > > Here's v2 which optimizes this function by not walking if > !PRIMARY_TEMPLATE_P (since in that case the innermost arguments have > already been walked when instantiating the context), and walking only > non-type arguments: > > -- >8 > > Subject: [PATCH] c++: improve "NTTP argument considered unused" fix [PR53164, > PR105848] > > PR c++/53164 > PR c++/105848 > > gcc/cp/ChangeLog: > > * pt.cc (instantiate_class_template): Call > mark_template_arguments_used. > (tsubst_copy_and_build) : Revert r13-995 change. > (mark_template_arguments_used): Define. > (instantiate_template): Call mark_template_arguments_used. > > gcc/testsuite/ChangeLog: > > * g++.dg/template/fn-ptr3a.C: New test. > * g++.dg/template/fn-ptr4.C: New test. > --- > gcc/cp/pt.cc | 57 +++++++++++++++++------- > gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 +++++++++++ > gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 ++++++ > 3 files changed, 80 insertions(+), 16 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr4.C > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > index 3bb98ebeac1..a87366bb616 100644 > --- a/gcc/cp/pt.cc > +++ b/gcc/cp/pt.cc > @@ -220,6 +220,7 @@ static tree make_argument_pack (tree); > static tree enclosing_instantiation_of (tree tctx); > static void instantiate_body (tree pattern, tree args, tree d, bool nested); > static tree maybe_dependent_member_ref (tree, tree, tsubst_flags_t, tree); > +static void mark_template_arguments_used (tree, tree); > > /* Make the current scope suitable for access checking when we are > processing T. T can be FUNCTION_DECL for instantiated function > @@ -12152,6 +12153,9 @@ instantiate_class_template (tree type) > cp_unevaluated_operand = 0; > c_inhibit_evaluation_warnings = 0; > } > + > + mark_template_arguments_used (templ, CLASSTYPE_TI_ARGS (type)); > + > /* Use #pragma pack from the template context. */ > saved_maximum_field_alignment = maximum_field_alignment; > maximum_field_alignment = TYPE_PRECISION (pattern); > @@ -21192,22 +21196,10 @@ tsubst_copy_and_build (tree t, > } > > /* Remember that there was a reference to this entity. */ > - if (function != NULL_TREE) > - { > - tree inner = function; > - if (TREE_CODE (inner) == ADDR_EXPR > - && TREE_CODE (TREE_OPERAND (inner, 0)) == FUNCTION_DECL) > - /* We should already have called mark_used when taking the > - address of this function, but do so again anyway to make > - sure it's odr-used: at worst this is a no-op, but if we > - obtained this FUNCTION_DECL as part of ahead-of-time overload > - resolution then that call to mark_used wouldn't have marked it > - odr-used yet (53164). */ > - inner = TREE_OPERAND (inner, 0); > - if (DECL_P (inner) > - && !mark_used (inner, complain) && !(complain & tf_error)) > - RETURN (error_mark_node); > - } > + if (function != NULL_TREE > + && DECL_P (function) > + && !mark_used (function, complain) && !(complain & tf_error)) > + RETURN (error_mark_node); > > if (!maybe_fold_fn_template_args (function, complain)) > return error_mark_node; > @@ -21902,6 +21894,37 @@ check_instantiated_args (tree tmpl, tree args, tsubst_flags_t complain) > return result; > } > > +/* Call mark_used on each entity within the non-type template arguments in > + ARGS for a specialization of TMPL, to ensure that each such entity is > + considered odr-used regardless of whether the specialization was first > + formed in a template context. > + > + This function assumes push_to_top_level has been called beforehand, and > + that processing_template_decl is set iff the template arguments are > + dependent. */ > + > +static void > +mark_template_arguments_used (tree tmpl, tree args) > +{ > + /* It suffices to do this only when fully specializing a primary template. */ > + if (processing_template_decl || !PRIMARY_TEMPLATE_P (tmpl)) > + return; > + > + /* We already marked outer arguments when specializing the context. */ > + args = INNERMOST_TEMPLATE_ARGS (args); > + > + for (tree arg : tree_vec_range (args)) > + if (!TYPE_P (arg)) > + { > + auto mark_used_r = [](tree *tp, int *, void *) { > + if (DECL_P (*tp)) > + mark_used (*tp, tf_none); > + return NULL_TREE; > + }; > + cp_walk_tree_without_duplicates (&args, mark_used_r, nullptr); Do we really need to walk into the args? > + } > +} > + > /* We're out of SFINAE context now, so generate diagnostics for the access > errors we saw earlier when instantiating D from TMPL and ARGS. */ > > @@ -22031,6 +22054,8 @@ instantiate_template (tree tmpl, tree orig_args, tsubst_flags_t complain) > push_nested_class (ctx); > } > > + mark_template_arguments_used (gen_tmpl, targ_ptr); > + > tree pattern = DECL_TEMPLATE_RESULT (gen_tmpl); > > fndecl = NULL_TREE; > diff --git a/gcc/testsuite/g++.dg/template/fn-ptr3a.C b/gcc/testsuite/g++.dg/template/fn-ptr3a.C > new file mode 100644 > index 00000000000..7456be5d51f > --- /dev/null > +++ b/gcc/testsuite/g++.dg/template/fn-ptr3a.C > @@ -0,0 +1,25 @@ > +// PR c++/53164 > +// PR c++/105848 > +// A stricter version of fn-ptr3.C that verifies using f as a template > +// argument alone constitutes an odr-use. > + > +template > +void f(T) { T::fail; } // { dg-error "fail" } > + > +template > +struct A { > + static void wrap(); > +}; > + > +template > +void wrap(); > + > +template > +void g() { > + A::wrap(); // { dg-message "required from here" } > + wrap(); // { dg-message "required from here" } > +} > + > +int main() { > + g<0>(); > +} > diff --git a/gcc/testsuite/g++.dg/template/fn-ptr4.C b/gcc/testsuite/g++.dg/template/fn-ptr4.C > new file mode 100644 > index 00000000000..36551ec5d7f > --- /dev/null > +++ b/gcc/testsuite/g++.dg/template/fn-ptr4.C > @@ -0,0 +1,14 @@ > +// { dg-do compile } > + > +template > +void wrap() { > + P(); // OK, despite A::g not being accessible from here. > +} > + > +struct A { > + static void f() { > + wrap(); > + } > +private: > + static void g(); > +};