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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id o2-20020a375a02000000b0074411b03972sm806964qkb.51.2023.03.31.10.28.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 31 Mar 2023 10:28:43 -0700 (PDT) Message-ID: <8fe724c0-aa3c-a35d-63dd-7e5c890969ea@redhat.com> Date: Fri, 31 Mar 2023 13:28:42 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 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> <1aca5d63-ec57-abc2-422f-68b197bb6c47@idea> From: Jason Merrill In-Reply-To: <1aca5d63-ec57-abc2-422f-68b197bb6c47@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=-12.5 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 3/31/23 11:55, Patrick Palka wrote: > On Fri, 31 Mar 2023, Patrick Palka wrote: > >> On Thu, 30 Mar 2023, Jason Merrill wrote: >> >>> On 3/30/23 14:53, Patrick Palka wrote: >>>> On Wed, 29 Mar 2023, Jason Merrill wrote: >>>> >>>>> 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. >>>> >>>> Indeed we do, the commit message was just rather sloppy/inaccurate... >>>> I'll try to correct it. >>>> >>>>> >>>>>>> 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? >>>> >>>> Hmm, I think we might need to some sort for walking for class NTTP >>>> arguments since they could be nested CONSTRUCTORs. But for non-class >>>> arguments we know that an entity will only appear as a pointer- or >>>> reference-to-function/variable, so we could pattern match for such a >>>> structure directly. And doing so should be preferable because >>>> cp_walk_tree is relatively expensive and this is a relatively hot code >>>> path. So maybe the following would be preferable? >>>> >>>> -- >8 -- >>>> >>>> Subject: [PATCH] c++: improve "NTTP argument considered unused" fix >>>> [PR53164, >>>> PR105848] >>>> >>>> r13-995-g733a792a2b2e16 worked around the problem of (pointer to) >>>> function NTTP arguments not always getting marked as odr-used by >>>> redundantly calling mark_used on the substituted ADDR_EXPR callee of a >>>> CALL_EXPR. That is just a narrow workaround however, since it assumes >>>> the function is later called. But the use as a template argument alone >>>> should constitute an odr-use of the function (since template arguments >>>> are an evaluated context, and we need its address); we shouldn't need to >>>> subsequently call or otherwise use the NTTP argument. >>>> >>>> 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 in 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. And as the second testcase >>>> below illustrates, we also need to walk C++20 class NTTP arguments which >>>> can in theory be large and thus expensive to walk repeatedly. The >>>> change to invalid_tparm_referent_p is needed to avoid bogusly rejecting >>>> the testcase's class NTTP arguments containing function pointers. >>>> >>>> (The third testcase is unrelated to this fix, but it helped rule out an >>>> earlier approach I was considering and it seems we don't have existing >>>> test coverage for this situation.) >>>> >>>> PR c++/53164 >>>> PR c++/105848 >>>> >>>> gcc/cp/ChangeLog: >>>> >>>> * pt.cc (invalid_tparm_referent_p): Accept ADDR_EXPR of >>>> FUNCTION_DECL. >>>> (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-ptr3b.C: New test. >>>> * g++.dg/template/fn-ptr4.C: New test. >>>> --- >>>> gcc/cp/pt.cc | 78 ++++++++++++++++++------ >>>> gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 ++++++++ >>>> gcc/testsuite/g++.dg/template/fn-ptr3b.C | 28 +++++++++ >>>> gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 +++++ >>>> 4 files changed, 127 insertions(+), 18 deletions(-) >>>> create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C >>>> create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3b.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 e514a277872..01ab220320c 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 >>>> @@ -7142,12 +7143,13 @@ invalid_tparm_referent_p (tree type, tree expr, >>>> tsubst_flags_t complain) >>>> decl = TREE_OPERAND (decl, 0); >>>> } >>>> - if (!VAR_P (decl)) >>>> + if (!VAR_OR_FUNCTION_DECL_P (decl)) >>>> { >>>> if (complain & tf_error) >>>> error_at (cp_expr_loc_or_input_loc (expr), >>>> "%qE is not a valid template argument of type %qT " >>>> - "because %qE is not a variable", expr, type, decl); >>>> + "because %qE is not a variable or function", >>>> + expr, type, decl); >>>> return true; >>>> } >>>> else if (cxx_dialect < cxx11 && !DECL_EXTERNAL_LINKAGE_P (decl)) >>>> @@ -12152,6 +12154,9 @@ 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 +21197,10 @@ 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 +21895,53 @@ 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)) >>>> + { >>>> + /* A (pointer/reference to) function or variable NTTP argument. */ >>>> + if (TREE_CODE (arg) == ADDR_EXPR >>>> + || TREE_CODE (arg) == INDIRECT_REF) >>>> + { >>>> + while (TREE_CODE (arg) == ADDR_EXPR >>>> + || REFERENCE_REF_P (arg) >>>> + || CONVERT_EXPR_P (arg)) >>>> + arg = TREE_OPERAND (arg, 0); >>>> + if (DECL_P (arg)) >>>> + mark_used (arg, tf_none); >>> >>> Passing tf_none and also ignoring the return value needs a comment justifying >>> why you assume it can't fail. >> >> *nod* Since these calls to mark_used ought to be at worst redundant, it >> should be safe to even assert >> >> bool ok = mark_used (arg, tf_none); >> gcc_checking_assert (ok || seen_error ()); >> >>> >>>> + } >>>> + /* A class NTTP argument. */ >>>> + else if (VAR_P (arg) >>>> + && DECL_NTTP_OBJECT_P (arg)) >>> >>> Maybe avoid doing this multiple times for the same NTTP object by gating it on >>> DECL_ODR_USED (arg)? >> >> Looks like these VAR_DECLs don't have DECL_LANG_SPECIFIC, so we can't >> inspect DECL_ODR_USED for them.. >> >> It occurred to me that instantiate_class_template is perhaps the wrong >> place to do this marking; it'd be more appropriate to do it in >> lookup_template_class when forming the type specialization rather than >> when instantiating its definition. So in order to handle all template >> kinds consistently, I think we should do the marking in either >> instantiate_class_template and instantiate_body (i.e. at instantiation >> time), or in lookup_template_class and instantiate_template (i.e. at >> specialization time), but currently the patch does it in >> instantiate_class_template and instantiate_template which sounds >> consistent but it's sadly not. >> However, lookup_template_class doesn't seem to call push_to_top_level at >> all, so if we want to call mark_used uninhibited on the template >> arguments from there I think we need to add a flag to mark_used that >> simply disables its >> >> if (processing_template_decl || in_template_function ()) >> return true; >> >> early exit. IIUC the purpose of this early exit is to avoid >> instantiating a template due to a use from an uninstantiated template, >> under the assumption that we'll call mark_used again at instantiation >> time for that use, but in this case it seems we need to allow such >> ahead-of-time instantiation since we don't reprocess the template >> arguments of a non-dependent specialization again at instantiation time. >> >> This is quite the can of worms :/ Yes, I think I'd prefer to move toward the instantiate_class_template/instantiate_body consistency, to avoid unnecessary marking in uninstantiated templates. > This is what I have so far, it's imperfect but perhaps good enough? > bootstrapped and regtested on x86_64-pc-linux-gnu: > > -- >8 -- > > Subject: [PATCH] c++: improve "NTTP argument considered unused" fix [PR53164, > PR105848] > > PR c++/53164 > PR c++/105848 > > gcc/cp/ChangeLog: > > * pt.cc (invalid_tparm_referent_p): Accept ADDR_EXPR of > FUNCTION_DECL. > (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-ptr3b.C: New test. > * g++.dg/template/fn-ptr4.C: New test. > --- > gcc/cp/pt.cc | 88 +++++++++++++++++++----- > gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 +++++++ > gcc/testsuite/g++.dg/template/fn-ptr3b.C | 28 ++++++++ > gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 ++++ > 4 files changed, 137 insertions(+), 18 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3b.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 dd7f0db9658..83902b0be8d 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 > @@ -7142,12 +7143,13 @@ invalid_tparm_referent_p (tree type, tree expr, tsubst_flags_t complain) > decl = TREE_OPERAND (decl, 0); > } > > - if (!VAR_P (decl)) > + if (!VAR_OR_FUNCTION_DECL_P (decl)) > { > if (complain & tf_error) > error_at (cp_expr_loc_or_input_loc (expr), > "%qE is not a valid template argument of type %qT " > - "because %qE is not a variable", expr, type, decl); > + "because %qE is not a variable or function", > + expr, type, decl); > return true; > } > else if (cxx_dialect < cxx11 && !DECL_EXTERNAL_LINKAGE_P (decl)) > @@ -12152,6 +12154,9 @@ 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 +21197,10 @@ 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 +21895,63 @@ 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 (and therefore marked for instantiation) regardless of > + whether the specialization was first formed in a template context (which > + inhibits mark_used). > + > + 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)) > + { > + /* A (pointer/reference to) function or variable NTTP argument. */ > + if (TREE_CODE (arg) == ADDR_EXPR > + || TREE_CODE (arg) == INDIRECT_REF) > + { > + while (TREE_CODE (arg) == ADDR_EXPR > + || REFERENCE_REF_P (arg) > + || CONVERT_EXPR_P (arg)) > + arg = TREE_OPERAND (arg, 0); > + if (VAR_OR_FUNCTION_DECL_P (arg)) > + { > + /* Pass tf_none to avoid duplicate diagnostics: the call > + ought to succeed without error, or a previous call > + must have already issued an error. */ > + bool ok = mark_used (arg, tf_none); > + gcc_checking_assert (ok || seen_error ()); > + } > + } > + /* A class NTTP argument. */ > + else if (VAR_P (arg) > + && DECL_NTTP_OBJECT_P (arg)) > + { > + auto mark_used_r = [](tree *tp, int *, void *) { > + if (VAR_OR_FUNCTION_DECL_P (*tp)) > + { > + bool ok = mark_used (*tp, tf_none); > + gcc_checking_assert (ok || seen_error ()); > + } > + return NULL_TREE; > + }; > + cp_walk_tree_without_duplicates (&DECL_INITIAL (arg), > + mark_used_r, nullptr); > + } > + } > +} > + > /* 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 +22081,8 @@ 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-ptr3b.C b/gcc/testsuite/g++.dg/template/fn-ptr3b.C > new file mode 100644 > index 00000000000..90d988ce896 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/template/fn-ptr3b.C > @@ -0,0 +1,28 @@ > +// PR c++/53164 > +// PR c++/105848 > +// A C++20 version of fn-ptr3a.C using class NTTPs. > +// { dg-do compile { target c++20 } } > + > +template > +void f(T) { T::fail; } // { dg-error "fail" } > + > +struct B_int { void (*P)(int); }; > +struct B_char { void (*P)(char); }; > + > +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(); > +};