From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id C2FD03858D28 for ; Fri, 31 Mar 2023 15:26:02 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org C2FD03858D28 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680276362; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zD+BxkLGBZ7Xed8IZwNCN14GOEd/ziguCll6peVQya0=; b=XGEx8/aYUUwSC+U2L7oLCt/N7w8FdgweSdHYcw1Rs08ggGPvzLXifJmeWjToAz/vxohjx0 97Gc54MITch5myyxaggqLMqEfvM2wOq+0MpSAR1cJ7WJULFlOcANUmUP3iNK0xUX26o5fN EOzH0CczvyH0oNta0x6oPSchh9OTgwY= Received: from mail-qv1-f71.google.com (mail-qv1-f71.google.com [209.85.219.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-18-9S5xR0LPNEmbaE7_KlEutQ-1; Fri, 31 Mar 2023 11:26:00 -0400 X-MC-Unique: 9S5xR0LPNEmbaE7_KlEutQ-1 Received: by mail-qv1-f71.google.com with SMTP id f3-20020a0cc303000000b005c9966620daso9809556qvi.4 for ; Fri, 31 Mar 2023 08:26:00 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680276360; h=mime-version:references:message-id:in-reply-to:subject:cc:to:date :from:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=zD+BxkLGBZ7Xed8IZwNCN14GOEd/ziguCll6peVQya0=; b=HauFQiI0BJizcyt361kWBCsnebUsY2eU4edAHKNww+MVRp28u3Duc8LxqDi+M8S2I9 tv83cd4GsqFdo+57YH1uLoALNMHQ5QA8s5BAMhV1lrKlJOiYWaOjwLsnQlsx1pz8EFza WMQ9WKw5biAmX9OBWiu0dyIz7nNsCneNMsmtiVHc97hdQZR6AY00UwjilkayH5h/O+ks SfuSehZd81MuIKySqRJsrpBujY1+/JrGnLI3wdYR+Sbq1oEi5k7Isw0Gdqri6bNcGPWw WE/cLZm+285+91yuY3OYpr8RT0OCSjxsj8Ey3B2jgn4imJ521yAew9bbbrC76u/KJqbE 2m8Q== X-Gm-Message-State: AAQBX9dZLHtvBIO/kPfP42Yvp9HzrD2T2PSgS3XquofOvQ+4xkGbhAPH /Hj6W0QS+GASFuRfWcMSdvGgvifL0qo1qOxjDq+yRjL9IGhixfWUz6j3EfVwjsVR5mwao/deoJ+ mDTmVjFzy+kZFBmxtZg== X-Received: by 2002:a05:6214:27ee:b0:5c8:b343:f749 with SMTP id jt14-20020a05621427ee00b005c8b343f749mr38058194qvb.22.1680276359749; Fri, 31 Mar 2023 08:25:59 -0700 (PDT) X-Google-Smtp-Source: AKy350ZPWZW/nSg0Lbc26wwQcArpXbsbCtO3FGLXdfR0W77eSeDXC5rSJW92YMnG3J2G6p/7hZHUmg== X-Received: by 2002:a05:6214:27ee:b0:5c8:b343:f749 with SMTP id jt14-20020a05621427ee00b005c8b343f749mr38058146qvb.22.1680276359203; Fri, 31 Mar 2023 08:25:59 -0700 (PDT) Received: from [192.168.1.130] (ool-457670bb.dyn.optonline.net. [69.118.112.187]) by smtp.gmail.com with ESMTPSA id ei15-20020ad45a0f000000b005dd8b9345c3sm536546qvb.91.2023.03.31.08.25.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Mar 2023 08:25:58 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Fri, 31 Mar 2023 11:25:58 -0400 (EDT) To: Jason Merrill cc: Patrick Palka , gcc-patches@gcc.gnu.org Subject: Re: [PATCH 1/2] c++: improve "NTTP argument considered unused" fix [PR53164, PR105848] In-Reply-To: Message-ID: References: <20230323211803.396326-1-ppalka@redhat.com> <4a04306f-faa9-5dd8-c850-05aa4a21d36e@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=-13.9 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_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 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 :/ > > > + { > > + 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 (&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 +22071,8 @@ 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(); > > +}; > >