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 104EB3858D28 for ; Wed, 25 Jan 2023 20:35:25 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 104EB3858D28 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=1674678924; 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=PbLN2M2dx/7IrkSomCVt00TNHq2rdF1Dn0hLtbWmeMk=; b=TSBv2AECPa7eZjqIofQIlnlaCEqyTx9o00Aq3m/wbYqwlmvG9DZwaZ+Z35hKD5vHbB7O+C MS5KiXugXQvnB4FqBLxRQa6RBXXLVKku8cfJEV4xOkeO7PtmvLUuEVO1OoRvBECuB2f7dC LtQkRYbMksyyvG60EKGwnnbfNK5PrMo= Received: from mail-vk1-f198.google.com (mail-vk1-f198.google.com [209.85.221.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-612-NwC_X8iyOhm3jmbXIOiSnQ-1; Wed, 25 Jan 2023 15:35:23 -0500 X-MC-Unique: NwC_X8iyOhm3jmbXIOiSnQ-1 Received: by mail-vk1-f198.google.com with SMTP id u187-20020a1fabc4000000b003ca3e899f8fso7842695vke.22 for ; Wed, 25 Jan 2023 12:35:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; 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=PbLN2M2dx/7IrkSomCVt00TNHq2rdF1Dn0hLtbWmeMk=; b=XcGEbflawPU6hQtp7H2dsWjGymTAEt2GJdrCEcJ3XfYDx5IBNPZYH9jgBGkvNDvVgx H9wP78QZZoFbJiPcHVSdGiVoIl+iNzQxm9vJCzSt8LtuEm36WfvZYZOR9uhpcO5NK2TP NkFPoO0XJZT8wSLPz10x7+xPsixGmWAI+3FRaTWm2EuMw9AU+/Z4BKarJm60+6Fe2tgJ Zb40NzuQ6jBuxt9py8ZffhVBaw5rmPo2QcMLvMheLx+DZjzY+iVEu9kI4jlgOoivIl6s bPLxBPZa+gLB6uVDtSrUsH9wYeosmUs3hld9gOokbUH3F6f1hk+xYm4ufaKw9XJXZJRt wpYQ== X-Gm-Message-State: AFqh2krU9EqASuMBQMNtVmxPttDGglP6hbHJDS0LQDiSEwS6OzrOx7Dj MwVUUFlICBF9HnPQLRuAkxpNLq29a052rYwAVhiDTosURxTtHY8nfw567WgSpIw0l3/IF6pSzoW Oq0DvI9NoG6kqp9ahpQ== X-Received: by 2002:a05:6102:c88:b0:3c6:d639:f1ac with SMTP id f8-20020a0561020c8800b003c6d639f1acmr23980552vst.22.1674678922624; Wed, 25 Jan 2023 12:35:22 -0800 (PST) X-Google-Smtp-Source: AMrXdXviPzEbDQUGzbNSrPclzTLV4ugJcMzt+iKHu8tPJFdbVpVBTxm4Hbo3cvr5x3jcbiiVtXzTDg== X-Received: by 2002:a05:6102:c88:b0:3c6:d639:f1ac with SMTP id f8-20020a0561020c8800b003c6d639f1acmr23980525vst.22.1674678922150; Wed, 25 Jan 2023 12:35:22 -0800 (PST) Received: from [192.168.1.130] (ool-457670bb.dyn.optonline.net. [69.118.112.187]) by smtp.gmail.com with ESMTPSA id s28-20020a05620a081c00b00705e7daf6f0sm4092435qks.129.2023.01.25.12.35.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Jan 2023 12:35:21 -0800 (PST) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Wed, 25 Jan 2023 15:35:20 -0500 (EST) To: Jason Merrill cc: Patrick Palka , Jonathan Wakely , libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org, Marek Polacek Subject: Re: [PATCH] c++: Define built-in for std::tuple_element [PR100157] In-Reply-To: <235cd04b-dd0d-9a3d-c371-f72baf407d7e@redhat.com> Message-ID: References: <20220707171436.1419387-1-jwakely@redhat.com> <2c2d32db-170d-d6b7-d04f-6cf27e157321@idea> <5ea335c0-c12a-59d6-4dfb-d62b402654d2@idea> <235cd04b-dd0d-9a3d-c371-f72baf407d7e@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-14.0 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 Tue, 17 Jan 2023, Jason Merrill wrote: > On 1/9/23 14:25, Patrick Palka via Gcc-patches wrote: > > On Mon, 9 Jan 2023, Patrick Palka wrote: > > > > > On Wed, 5 Oct 2022, Patrick Palka wrote: > > > > > > > On Thu, 7 Jul 2022, Jonathan Wakely via Gcc-patches wrote: > > > > > > > > > This adds a new built-in to replace the recursive class template > > > > > instantiations done by traits such as std::tuple_element and > > > > > std::variant_alternative. The purpose is to select the Nth type from a > > > > > list of types, e.g. __builtin_type_pack_element(1, char, int, float) > > > > > is > > > > > int. > > > > > > > > > > For a pathological example tuple_element_t<1000, tuple<2000 types...>> > > > > > the compilation time is reduced by more than 90% and the memory used > > > > > by > > > > > the compiler is reduced by 97%. In realistic examples the gains will > > > > > be > > > > > much smaller, but still relevant. > > > > > > > > > > Clang has a similar built-in, __type_pack_element, but that's > > > > > a > > > > > "magic template" built-in using <> syntax, which GCC doesn't support. > > > > > So > > > > > this provides an equivalent feature, but as a built-in function using > > > > > parens instead of <>. I don't really like the name "type pack element" > > > > > (it gives you an element from a pack of types) but the > > > > > semi-consistency > > > > > with Clang seems like a reasonable argument in favour of keeping the > > > > > name. I'd be open to alternative names though, e.g. __builtin_nth_type > > > > > or __builtin_type_at_index. > > > > > > > > Rather than giving the trait a different name from __type_pack_element, > > > > I wonder if we could just special case cp_parser_trait to expect <> > > > > instead of parens for this trait? > > > > > > > > Btw the frontend recently got a generic TRAIT_TYPE tree code, which gets > > > > rid of much of the boilerplate of adding a new type-yielding built-in > > > > trait, see e.g. cp-trait.def. > > > > > > Here's a tested patch based on Jonathan's original patch that implements > > > the built-in in terms of TRAIT_TYPE, names it __type_pack_element > > > instead of __builtin_type_pack_element, and treats invocations of it > > > like a template-id instead of a call (to match Clang). > > > > > > -- >8 -- > > > > > > Subject: [PATCH] c++: Define built-in for std::tuple_element [PR100157] > > > > > > This adds a new built-in to replace the recursive class template > > > instantiations done by traits such as std::tuple_element and > > > std::variant_alternative. The purpose is to select the Nth type from a > > > list of types, e.g. __type_pack_element<1, char, int, float> is int. > > > We implement it as a special kind of TRAIT_TYPE. > > > > > > For a pathological example tuple_element_t<1000, tuple<2000 types...>> > > > the compilation time is reduced by more than 90% and the memory used by > > > the compiler is reduced by 97%. In realistic examples the gains will be > > > much smaller, but still relevant. > > > > > > Unlike the other built-in traits, __type_pack_element uses template-id > > > syntax instead of call syntax and is SFINAE-enabled, matching Clang's > > > implementation. And like the other built-in traits, it's not mangleable > > > so we can't use it directly in function signatures. > > > > > > Some caveats: > > > > > > * Clang's version of the built-in seems to act like a "magic template" > > > that can e.g. be used as a template template argument. For > > > simplicity > > > we implement it in a more ad-hoc way. > > > * Our parsing of the <>'s in __type_pack_element<...> is currently > > > rudimentary and doesn't try to disambiguate a trailing >> vs > > > > > as cp_parser_enclosed_template_argument_list does. > > > > Hmm, this latter caveat turns out to be inconvenient (for code such as > > type_pack_element3.C) and admits an easy workaround inspired by what > > cp_parser_enclosed_template_argument_list does. > > > > v2: Consider the >> in __type_pack_element<0, int, char>> to be two >'s. > > Handle non-type TRAIT_TYPE_TYPE1 in strip_typedefs (for sake of > > CPTK_TYPE_PACK_ELEMENT). > > Why not use cp_parser_enclosed_template_argument_list directly? If we used cp_parser_enclosed_template_argument_list we would then need to convert the returned TREE_VEC into a TREE_LIST and also diagnose argument kind mismatches (i.e. verify the first argument is an expression and the rest are types). It seemed like more complexity overall then just duplicating the >> splitting logic, but I can do that if you prefer? > > > -- >8 -- > > > > Subject: [PATCH] c++: Define built-in for std::tuple_element [PR100157] > > > > This adds a new built-in to replace the recursive class template > > instantiations done by traits such as std::tuple_element and > > std::variant_alternative. The purpose is to select the Nth type from a > > list of types, e.g. __type_pack_element<1, char, int, float> is int. > > We implement it as a special kind of TRAIT_TYPE. > > > > For a pathological example tuple_element_t<1000, tuple<2000 types...>> > > the compilation time is reduced by more than 90% and the memory used by > > the compiler is reduced by 97%. In realistic examples the gains will be > > much smaller, but still relevant. > > > > Unlike the other built-in traits, __type_pack_element uses template-id > > syntax instead of call syntax and is SFINAE-enabled, matching Clang's > > implementation. And like the other built-in traits, it's not mangleable > > so we can't use it directly in function signatures. > > > > N.B. Clang seems to implement __type_pack_element as a first-class > > template that can e.g. be used as a template template argument. For > > simplicity we implement it in a more ad-hoc way. > > > > Co-authored-by: Jonathan Wakely > > > > PR c++/100157 > > > > gcc/cp/ChangeLog: > > > > * cp-trait.def (TYPE_PACK_ELEMENT): Define. > > * cp-tree.h (finish_trait_type): Add complain parameter. > > * cxx-pretty-print.cc (pp_cxx_trait): Handle > > CPTK_TYPE_PACK_ELEMENT. > > * parser.cc (cp_parser_constant_expression): Document default > > arguments. > > (cp_parser_trait): Handle CPTK_TYPE_PACK_ELEMENT. Pass > > tf_warning_or_error to finish_trait_type. > > * pt.cc (tsubst) : Handle > > CPTK_TYPE_PACK_ELEMENT. > > * semantics.cc (finish_type_pack_element): Define. > > (finish_trait_type): Add complain parameter. Handle > > CPTK_TYPE_PACK_ELEMENT. > > * tree.cc (strip_typedefs): Handle non-type TRAIT_TYPE_TYPE1. > > Pass tf_warning_or_error to finish_trait_type. > > * typeck.cc (structural_comptypes) : Use > > cp_tree_equal instead of same_type_p for TRAIT_TYPE_TYPE1. > > > > libstdc++-v3/ChangeLog: > > > > * include/bits/utility.h (_Nth_type): Conditionally define in > > terms of __type_pack_element if available. > > > > gcc/testsuite/ChangeLog: > > > > * g++.dg/ext/type_pack_element1.C: New test. > > * g++.dg/ext/type_pack_element2.C: New test. > > * g++.dg/ext/type_pack_element3.C: New test. > > --- > > gcc/cp/cp-trait.def | 1 + > > gcc/cp/cp-tree.h | 2 +- > > gcc/cp/cxx-pretty-print.cc | 17 +++++-- > > gcc/cp/parser.cc | 46 +++++++++++++++---- > > gcc/cp/pt.cc | 8 +++- > > gcc/cp/semantics.cc | 39 +++++++++++++++- > > gcc/cp/tree.cc | 10 ++-- > > gcc/cp/typeck.cc | 2 +- > > gcc/testsuite/g++.dg/ext/type_pack_element1.C | 19 ++++++++ > > gcc/testsuite/g++.dg/ext/type_pack_element2.C | 14 ++++++ > > gcc/testsuite/g++.dg/ext/type_pack_element3.C | 22 +++++++++ > > libstdc++-v3/include/bits/utility.h | 6 +++ > > 12 files changed, 165 insertions(+), 21 deletions(-) > > create mode 100644 gcc/testsuite/g++.dg/ext/type_pack_element1.C > > create mode 100644 gcc/testsuite/g++.dg/ext/type_pack_element2.C > > create mode 100644 gcc/testsuite/g++.dg/ext/type_pack_element3.C > > > > diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def > > index 823899a26c5..63f6b101eeb 100644 > > --- a/gcc/cp/cp-trait.def > > +++ b/gcc/cp/cp-trait.def > > @@ -89,6 +89,7 @@ DEFTRAIT_TYPE (REMOVE_CV, "__remove_cv", 1) > > DEFTRAIT_TYPE (REMOVE_REFERENCE, "__remove_reference", 1) > > DEFTRAIT_TYPE (REMOVE_CVREF, "__remove_cvref", 1) > > DEFTRAIT_TYPE (UNDERLYING_TYPE, "__underlying_type", 1) > > +DEFTRAIT_TYPE (TYPE_PACK_ELEMENT, "__type_pack_element", -1) > > /* These traits yield a type pack, not a type, and are represented by > > cp_parser_trait as a special BASES tree instead of a TRAIT_TYPE tree. > > */ > > diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h > > index 1f4967c2ba0..f3cc2c5874c 100644 > > --- a/gcc/cp/cp-tree.h > > +++ b/gcc/cp/cp-tree.h > > @@ -7764,7 +7764,7 @@ extern tree finish_decltype_type (tree, > > bool, tsubst_flags_t); > > extern tree fold_builtin_is_corresponding_member (location_t, int, tree > > *); > > extern tree fold_builtin_is_pointer_inverconvertible_with_class > > (location_t, int, tree *); > > extern tree finish_trait_expr (location_t, enum > > cp_trait_kind, tree, tree); > > -extern tree finish_trait_type (enum cp_trait_kind, > > tree, tree); > > +extern tree finish_trait_type (enum cp_trait_kind, > > tree, tree, tsubst_flags_t); > > extern tree build_lambda_expr (void); > > extern tree build_lambda_object (tree); > > extern tree begin_lambda_type (tree); > > diff --git a/gcc/cp/cxx-pretty-print.cc b/gcc/cp/cxx-pretty-print.cc > > index 8ca1b8f234a..07a0406e491 100644 > > --- a/gcc/cp/cxx-pretty-print.cc > > +++ b/gcc/cp/cxx-pretty-print.cc > > @@ -2625,8 +2625,16 @@ pp_cxx_trait (cxx_pretty_printer *pp, tree t) > > #undef DEFTRAIT > > } > > - pp_cxx_left_paren (pp); > > - pp->type_id (type1); > > + if (kind == CPTK_TYPE_PACK_ELEMENT) > > + { > > + pp_cxx_begin_template_argument_list (pp); > > + pp->expression (type1); > > + } > > + else > > + { > > + pp_cxx_left_paren (pp); > > + pp->type_id (type1); > > + } > > if (type2) > > { > > if (TREE_CODE (type2) != TREE_LIST) > > @@ -2641,7 +2649,10 @@ pp_cxx_trait (cxx_pretty_printer *pp, tree t) > > pp->type_id (TREE_VALUE (arg)); > > } > > } > > - pp_cxx_right_paren (pp); > > + if (kind == CPTK_TYPE_PACK_ELEMENT) > > + pp_cxx_end_template_argument_list (pp); > > + else > > + pp_cxx_right_paren (pp); > > } > > // requires-clause: > > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc > > index 8b1658decba..0a88d83d955 100644 > > --- a/gcc/cp/parser.cc > > +++ b/gcc/cp/parser.cc > > @@ -10683,9 +10683,9 @@ cp_parser_expression (cp_parser* parser, cp_id_kind > > * pidk, > > static cp_expr > > cp_parser_constant_expression (cp_parser* parser, > > - int allow_non_constant_p, > > - bool *non_constant_p, > > - bool strict_p) > > + int allow_non_constant_p /* = 0 */, > > + bool *non_constant_p /* = NULL */, > > + bool strict_p /* = false */) > > { > > bool saved_integral_constant_expression_p; > > bool saved_allow_non_integral_constant_expression_p; > > @@ -10912,12 +10912,25 @@ cp_parser_trait (cp_parser* parser, enum rid > > keyword) > > cp_lexer_consume_token (parser->lexer); > > matching_parens parens; > > - parens.require_open (parser); > > - { > > - type_id_in_expr_sentinel s (parser); > > - type1 = cp_parser_type_id (parser); > > - } > > + /* Unlike the other built-in traits, __type_pack_element is unique in > > that > > + it takes an expression as its first argument and it uses template-id > > + syntax instead of function call syntax (for compatibility with Clang). > > + We special case these properties of __type_pack_element here and > > elsewhere. > > + > > + TODO: Generalize the trait infrastructure so that __type_pack_element > > + is no longer a special case. */ > > + if (kind == CPTK_TYPE_PACK_ELEMENT) > > + { > > + cp_parser_require (parser, CPP_LESS, RT_LESS); > > + type1 = cp_parser_constant_expression (parser); > > + } > > + else > > + { > > + parens.require_open (parser); > > + type_id_in_expr_sentinel s (parser); > > + type1 = cp_parser_type_id (parser); > > + } > > if (type1 == error_mark_node) > > return error_mark_node; > > @@ -10953,7 +10966,20 @@ cp_parser_trait (cp_parser* parser, enum rid > > keyword) > > } > > location_t finish_loc = cp_lexer_peek_token (parser->lexer)->location; > > - parens.require_close (parser); > > + if (kind == CPTK_TYPE_PACK_ELEMENT) > > + { > > + /* As in cp_parser_enclosed_template_argument_list, a trailing > > + '>>' here is considered to be two separate '>' tokens. */ > > + if (cp_lexer_next_token_is (parser->lexer, CPP_RSHIFT)) > > + { > > + cp_token *token = cp_lexer_peek_token (parser->lexer); > > + token->type = CPP_GREATER; > > + } > > + else > > + cp_parser_require (parser, CPP_GREATER, RT_GREATER); > > + } > > + else > > + parens.require_close (parser); > > /* Construct a location of the form: > > __is_trivially_copyable(_Tp) > > @@ -10971,7 +10997,7 @@ cp_parser_trait (cp_parser* parser, enum rid > > keyword) > > return cp_expr (finish_bases (type1, true), trait_loc); > > default: > > if (type) > > - return finish_trait_type (kind, type1, type2); > > + return finish_trait_type (kind, type1, type2, tf_warning_or_error); > > else > > return finish_trait_expr (trait_loc, kind, type1, type2); > > } > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > > index cbe5898b553..2e83970a252 100644 > > --- a/gcc/cp/pt.cc > > +++ b/gcc/cp/pt.cc > > @@ -16576,9 +16576,13 @@ tsubst (tree t, tree args, tsubst_flags_t complain, > > tree in_decl) > > case TRAIT_TYPE: > > { > > - tree type1 = tsubst (TRAIT_TYPE_TYPE1 (t), args, complain, in_decl); > > + tree type1 = TRAIT_TYPE_TYPE1 (t); > > + if (TRAIT_TYPE_KIND (t) != CPTK_TYPE_PACK_ELEMENT) > > + type1 = tsubst (type1, args, complain, in_decl); > > + else > > + type1 = tsubst_copy_and_build (type1, args, complain, in_decl); > > tree type2 = tsubst (TRAIT_TYPE_TYPE2 (t), args, complain, in_decl); > > - type = finish_trait_type (TRAIT_TYPE_KIND (t), type1, type2); > > + type = finish_trait_type (TRAIT_TYPE_KIND (t), type1, type2, > > complain); > > return cp_build_qualified_type (type, > > cp_type_quals (t) | cp_type_quals > > (type), > > complain | tf_ignore_bad_quals); > > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc > > index ef5bf2430b1..af9edf59b3b 100644 > > --- a/gcc/cp/semantics.cc > > +++ b/gcc/cp/semantics.cc > > @@ -4457,6 +4457,36 @@ finish_underlying_type (tree type) > > return underlying_type; > > } > > +/* Implement the __type_pack_element keyword: Return the type > > + at index IDX within TYPES. */ > > + > > +static tree > > +finish_type_pack_element (tree idx, tree types, tsubst_flags_t complain) > > +{ > > + idx = maybe_constant_value (idx); > > + if (TREE_CODE (idx) != INTEGER_CST || !INTEGRAL_TYPE_P (TREE_TYPE (idx))) > > + { > > + if (complain & tf_error) > > + error ("%<__type_pack_element%> index is not an integral constant"); > > + return error_mark_node; > > + } > > + HOST_WIDE_INT val = tree_to_shwi (idx); > > + if (val < 0) > > + { > > + if (complain & tf_error) > > + error ("%<__type_pack_element%> index is negative"); > > + return error_mark_node; > > + } > > + tree result = chain_index (val, types); > > + if (!result) > > + { > > + if (complain & tf_error) > > + error ("%<__type_pack_element%> index is out of range"); > > + return error_mark_node; > > + } > > + return TREE_VALUE (result); > > +} > > + > > /* Implement the __direct_bases keyword: Return the direct base classes > > of type. */ > > @@ -12213,7 +12243,8 @@ finish_trait_expr (location_t loc, cp_trait_kind > > kind, tree type1, tree type2) > > /* Process a trait type. */ > > tree > > -finish_trait_type (cp_trait_kind kind, tree type1, tree type2) > > +finish_trait_type (cp_trait_kind kind, tree type1, tree type2, > > + tsubst_flags_t complain) > > { > > if (type1 == error_mark_node > > || type2 == error_mark_node) > > @@ -12237,17 +12268,23 @@ finish_trait_type (cp_trait_kind kind, tree type1, > > tree type2) > > { > > case CPTK_UNDERLYING_TYPE: > > return finish_underlying_type (type1); > > + > > case CPTK_REMOVE_CV: > > return cv_unqualified (type1); > > + > > case CPTK_REMOVE_REFERENCE: > > if (TYPE_REF_P (type1)) > > type1 = TREE_TYPE (type1); > > return type1; > > + > > case CPTK_REMOVE_CVREF: > > if (TYPE_REF_P (type1)) > > type1 = TREE_TYPE (type1); > > return cv_unqualified (type1); > > + case CPTK_TYPE_PACK_ELEMENT: > > + return finish_type_pack_element (type1, type2, complain); > > + > > #define DEFTRAIT_EXPR(CODE, NAME, ARITY) \ > > case CPTK_##CODE: > > #include "cp-trait.def" > > diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc > > index faf01616f87..d834a0fd38b 100644 > > --- a/gcc/cp/tree.cc > > +++ b/gcc/cp/tree.cc > > @@ -1792,14 +1792,18 @@ strip_typedefs (tree t, bool *remove_attributes /* = > > NULL */, > > break; > > case TRAIT_TYPE: > > { > > - tree type1 = strip_typedefs (TRAIT_TYPE_TYPE1 (t), > > - remove_attributes, flags); > > + tree type1 = TRAIT_TYPE_TYPE1 (t); > > + if (TYPE_P (type1)) > > + type1 = strip_typedefs (type1, remove_attributes, flags); > > + else > > + type1 = strip_typedefs_expr (type1, remove_attributes, flags); > > tree type2 = strip_typedefs (TRAIT_TYPE_TYPE2 (t), > > remove_attributes, flags); > > if (type1 == TRAIT_TYPE_TYPE1 (t) && type2 == TRAIT_TYPE_TYPE2 (t)) > > result = NULL_TREE; > > else > > - result = finish_trait_type (TRAIT_TYPE_KIND (t), type1, type2); > > + result = finish_trait_type (TRAIT_TYPE_KIND (t), type1, type2, > > + tf_warning_or_error); > > } > > break; > > case TYPE_PACK_EXPANSION: > > diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc > > index 69b1268cfec..f5548737e4c 100644 > > --- a/gcc/cp/typeck.cc > > +++ b/gcc/cp/typeck.cc > > @@ -1632,7 +1632,7 @@ structural_comptypes (tree t1, tree t2, int strict) > > case TRAIT_TYPE: > > if (TRAIT_TYPE_KIND (t1) != TRAIT_TYPE_KIND (t2)) > > return false; > > - if (!same_type_p (TRAIT_TYPE_TYPE1 (t1), TRAIT_TYPE_TYPE1 (t2)) > > + if (!cp_tree_equal (TRAIT_TYPE_TYPE1 (t1), TRAIT_TYPE_TYPE1 (t2)) > > || !cp_tree_equal (TRAIT_TYPE_TYPE2 (t1), TRAIT_TYPE_TYPE2 (t2))) > > return false; > > break; > > diff --git a/gcc/testsuite/g++.dg/ext/type_pack_element1.C > > b/gcc/testsuite/g++.dg/ext/type_pack_element1.C > > new file mode 100644 > > index 00000000000..46858555502 > > --- /dev/null > > +++ b/gcc/testsuite/g++.dg/ext/type_pack_element1.C > > @@ -0,0 +1,19 @@ > > +// { dg-do compile { target c++11 } } > > + > > +using ty0 = __type_pack_element<0, int>; > > +using ty0 = __type_pack_element<0, int, char>; > > +using ty0 = int; > > + > > +using ty1 = __type_pack_element<1, int, char>; > > +using ty1 = __type_pack_element<(6 - 5) * 1, int, char>; > > +using ty1 = char; > > + > > +template > > +using __const_type_pack_element_t = const __type_pack_element; > > + > > +using ty2 = __const_type_pack_element_t<2, int, char, long>; > > +using ty2 = const long; > > + > > +template struct A { }; > > +using ty3 = __type_pack_element<3, int, int, int, A>; > > +using ty3 = A; > > diff --git a/gcc/testsuite/g++.dg/ext/type_pack_element2.C > > b/gcc/testsuite/g++.dg/ext/type_pack_element2.C > > new file mode 100644 > > index 00000000000..363cfa92514 > > --- /dev/null > > +++ b/gcc/testsuite/g++.dg/ext/type_pack_element2.C > > @@ -0,0 +1,14 @@ > > +// { dg-do compile { target c++11 } } > > + > > +int p; > > + > > +using type = __type_pack_element<&p, int>; // { dg-error "not an integral > > constant" } > > +using type = __type_pack_element<1, int>; // { dg-error "out of range" } > > +using type = __type_pack_element<-1, int>; // { dg-error "negative" } > > +using type = __type_pack_element<2, int, char>; // { dg-error "out of > > range" } > > + > > +template > > +using __type_pack_element_t = __type_pack_element; > > +// { dg-error "out of range" "" { target *-*-* } .-1 } > > + > > +using type = __type_pack_element_t<3, int, char, long>; // { dg-message > > "here" } > > diff --git a/gcc/testsuite/g++.dg/ext/type_pack_element3.C > > b/gcc/testsuite/g++.dg/ext/type_pack_element3.C > > new file mode 100644 > > index 00000000000..269f84f464f > > --- /dev/null > > +++ b/gcc/testsuite/g++.dg/ext/type_pack_element3.C > > @@ -0,0 +1,22 @@ > > +// { dg-do compile { target c++11 } } > > + > > +template> > > +constexpr int f(int) { return 1; } > > + > > +template > > +constexpr int f(...) { return 2; }; > > + > > +int p; > > + > > +static_assert(f(0) == 1, ""); > > +static_assert(f(0) == 1, ""); > > +static_assert(f(0) == 2, ""); > > +static_assert(f(0) == 2, ""); > > + > > +template struct A; > > +template struct A> { > > }; > > +template struct A; > > + > > +template struct B; > > +template struct B> { }; > > +template struct B; > > diff --git a/libstdc++-v3/include/bits/utility.h > > b/libstdc++-v3/include/bits/utility.h > > index 6a192e27836..5d524d33b4c 100644 > > --- a/libstdc++-v3/include/bits/utility.h > > +++ b/libstdc++-v3/include/bits/utility.h > > @@ -224,6 +224,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > #endif // C++17 > > #endif // C++14 > > +#if __has_builtin(__type_pack_element) > > + template > > + struct _Nth_type > > + { using type = __type_pack_element<_Np, _Types...>; }; > > +#else > > template > > struct _Nth_type > > { }; > > @@ -262,6 +267,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...> > > { using type = _Tp1; }; > > #endif > > +#endif > > _GLIBCXX_END_NAMESPACE_VERSION > > } // namespace > >