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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id x19-20020ac87313000000b003e302c1f498sm696059qto.37.2023.03.31.08.55.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Mar 2023 08:55:06 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Fri, 31 Mar 2023 11:55:05 -0400 (EDT) To: Patrick Palka cc: Jason Merrill , gcc-patches@gcc.gnu.org Subject: Re: [PATCH 1/2] c++: improve "NTTP argument considered unused" fix [PR53164, PR105848] In-Reply-To: Message-ID: <1aca5d63-ec57-abc2-422f-68b197bb6c47@idea> 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 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 :/ 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(); +}; -- 2.40.0.153.g6369acd968