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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 919533858D28 for ; Wed, 6 Jul 2022 19:26:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 919533858D28 Received: from mail-qt1-f200.google.com (mail-qt1-f200.google.com [209.85.160.200]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-269-9QuUpSLWPzKyDFxlD65Xdg-1; Wed, 06 Jul 2022 15:26:13 -0400 X-MC-Unique: 9QuUpSLWPzKyDFxlD65Xdg-1 Received: by mail-qt1-f200.google.com with SMTP id f14-20020ac8068e000000b0031e899fabdcso4630911qth.5 for ; Wed, 06 Jul 2022 12:26:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:date:to:cc:subject:in-reply-to:message-id :references:mime-version; bh=e2muCUIPXMJGUva2mLzBxyANNebYqjIb0ZJ1+RFn+O8=; b=yBuzzY7fi6UQemKREZSPUdp0cOo7QrqH6HUblli4rnPOhd48LRNIq/O31+V/pLS/zi B00LjdBzmtH/fA3h8uF0MzfMrNVk8Wq/c25z0Z6usVl2yEraAEJYksWaA0fkOSfwwzE/ QSxzCHoc8msSAvhSpKs3+IXqNZ5qfad54veUkPc+fJDmnU9uFXDO42LQUyhaZ6h0KpGM SRvjNJdgXP+A7R5QWKxywY3NNxOIEbrW8S52NOC15Xj2dij3vWid5VvcZ1WOo3uPbGtK jE1vGE+vhF2xN0A/EdNUax9aDR8or8olizGrRE2LnQXz81zFumRj3poTTGGfNrAKWo8Y Dzyg== X-Gm-Message-State: AJIora+Gtfc5+lLBK1hcJBUDpOBq0jAOf1WW7GWu2/doM0oTw5Y76q/t oFqSGSBxFBu3dGAaqibewgrGydxKIlvDNzYB3ZDJohhJ73JofTHjZv6T+qHSnw+9PSxme236B6Q vJXPLQUaDKfjH0v7C4A== X-Received: by 2002:a05:6214:1ccd:b0:46e:7427:2626 with SMTP id g13-20020a0562141ccd00b0046e74272626mr39118688qvd.101.1657135572386; Wed, 06 Jul 2022 12:26:12 -0700 (PDT) X-Google-Smtp-Source: AGRyM1uI6K0RYVBhRza8KIqzGuPIecMOhTmykVNhBQqII6WRkmg/OrMGKgzepjFN45+YO0cXDX/pRw== X-Received: by 2002:a05:6214:1ccd:b0:46e:7427:2626 with SMTP id g13-20020a0562141ccd00b0046e74272626mr39118648qvd.101.1657135571809; Wed, 06 Jul 2022 12:26:11 -0700 (PDT) Received: from [192.168.1.130] (ool-457670bb.dyn.optonline.net. [69.118.112.187]) by smtp.gmail.com with ESMTPSA id o19-20020a05622a045300b00304ecf35b50sm26269052qtx.97.2022.07.06.12.26.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Jul 2022 12:26:11 -0700 (PDT) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Wed, 6 Jul 2022 15:26:10 -0400 (EDT) To: Jason Merrill cc: Patrick Palka , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] c++: generic targs and identity substitution [PR105956] In-Reply-To: <07a63134-41bb-4467-57b3-59d514940fb7@redhat.com> Message-ID: References: <20220629174236.3390391-1-ppalka@redhat.com> <9bc79bbc-bbe5-e8c9-2d09-ff02308ec754@idea> <07a63134-41bb-4467-57b3-59d514940fb7@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=-14.8 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_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 06 Jul 2022 19:26:19 -0000 On Tue, 5 Jul 2022, Jason Merrill wrote: > On 7/5/22 10:06, Patrick Palka wrote: > > On Fri, 1 Jul 2022, Jason Merrill wrote: > > > > > On 6/29/22 13:42, Patrick Palka wrote: > > > > In r13-1045-gcb7fd1ea85feea I assumed that substitution into generic > > > > DECL_TI_ARGS corresponds to an identity mapping of the given arguments, > > > > and hence its safe to always elide such substitution. But this PR > > > > demonstrates that such a substitution isn't always the identity mapping, > > > > in particular when there's an ARGUMENT_PACK_SELECT argument, which gets > > > > handled specially during substitution: > > > > > > > > * when substituting an APS into a template parameter, we strip the > > > > APS to its underlying argument; > > > > * and when substituting an APS into a pack expansion, we strip the > > > > APS to its underlying argument pack. > > > > > > Ah, right. For instance, in variadic96.C we have > > > > > > 10 template < typename... T > > > > 11 struct derived > > > 12 : public base< T, derived< T... > >... > > > > > > so when substituting into the base-specifier, we're approaching it from > > > the > > > outside in, so when we get to the inner T... we need some way to find the > > > T > > > pack again. It might be possible to remove the need for APS by > > > substituting > > > inner pack expansions before outer ones, which could improve worst-case > > > complexity, but I don't know how relevant that is in real code; I imagine > > > most > > > inner pack expansions are as simple as this one. > > > > Aha, that makes sense. > > > > > > > > > In this testcase, when expanding the pack expansion pattern (idx + > > > > Ns)... > > > > with Ns={0,1}, we specialize idx twice, first with Ns=APS<0,{0,1}> and > > > > then Ns=APS<1,{0,1}>. The DECL_TI_ARGS of idx are the generic template > > > > arguments of the enclosing class template impl, so before r13-1045, > > > > we'd substitute into its DECL_TI_ARGS which gave Ns={0,1} as desired. > > > > But after r13-1045, we elide this substitution and end up attempting to > > > > hash the original Ns argument, an APS, which ICEs. > > > > > > > > So this patch partially reverts this part of r13-1045. I considered > > > > using preserve_args in this case instead, but that'd break the > > > > static_assert in the testcase because preserve_args always strips APS to > > > > its underlying argument, but here we want to strip it to its underlying > > > > argument pack, so we'd incorrectly end up forming the specializations > > > > impl<0>::idx and impl<1>::idx instead of impl<0,1>::idx. > > > > > > > > Although we can't elide the substitution into DECL_TI_ARGS in light of > > > > ARGUMENT_PACK_SELECT, it should still be safe to elide template argument > > > > coercion in the case of a non-template decl, which this patch preserves. > > > > > > > > It's unfortunate that we need to remove this optimization just because > > > > it doesn't hold for one special tree code. So this patch implements a > > > > heuristic in tsubst_template_args to avoid allocating a new TREE_VEC if > > > > the substituted elements are identical to those of a level from ARGS. > > > > It turns out that about 30% of all calls to tsubst_template_args benefit > > > > from this optimization, and it reduces memory usage by about 1.5% for > > > > e.g. stdc++.h (relative to r13-1045). (This is the maybe_reuse stuff, > > > > the rest of the changes to tsubst_template_args are just drive-by > > > > cleanups.) > > > > > > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > > > > trunk? Patch generated with -w to ignore noisy whitespace changes. > > > > > > > > PR c++/105956 > > > > > > > > gcc/cp/ChangeLog: > > > > > > > > * pt.cc (tsubst_template_args): Move variable declarations > > > > closer to their first use. Replace 'orig_t' with 'r'. Rename > > > > 'need_new' to 'const_subst_p'. Heuristically detect if the > > > > substituted elements are identical to that of a level from > > > > 'args' and avoid allocating a new TREE_VEC if so. > > > > (tsubst_decl) : Revert > > > > r13-1045-gcb7fd1ea85feea change for avoiding substitution into > > > > DECL_TI_ARGS, but still avoid coercion in this case. > > > > > > > > gcc/testsuite/ChangeLog: > > > > > > > > * g++.dg/cpp0x/variadic183.C: New test. > > > > --- > > > > gcc/cp/pt.cc | 113 > > > > ++++++++++++++--------- > > > > gcc/testsuite/g++.dg/cpp0x/variadic183.C | 14 +++ > > > > 2 files changed, 85 insertions(+), 42 deletions(-) > > > > create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic183.C > > > > > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc > > > > index 8672da123f4..7898834faa6 100644 > > > > --- a/gcc/cp/pt.cc > > > > +++ b/gcc/cp/pt.cc > > > > @@ -27,6 +27,7 @@ along with GCC; see the file COPYING3. If not see > > > > Fixed by: C++20 modules. */ > > > > #include "config.h" > > > > +#define INCLUDE_ALGORITHM // for std::equal > > > > #include "system.h" > > > > #include "coretypes.h" > > > > #include "cp-tree.h" > > > > @@ -13544,17 +13545,22 @@ tsubst_argument_pack (tree orig_arg, tree > > > > args, > > > > tsubst_flags_t complain, > > > > tree > > > > tsubst_template_args (tree t, tree args, tsubst_flags_t complain, > > > > tree > > > > in_decl) > > > > { > > > > - tree orig_t = t; > > > > - int len, need_new = 0, i, expanded_len_adjust = 0, out; > > > > - tree *elts; > > > > - > > > > if (t == error_mark_node) > > > > return error_mark_node; > > > > - len = TREE_VEC_LENGTH (t); > > > > - elts = XALLOCAVEC (tree, len); > > > > + const int len = TREE_VEC_LENGTH (t); > > > > + tree *elts = XALLOCAVEC (tree, len); > > > > + int expanded_len_adjust = 0; > > > > - for (i = 0; i < len; i++) > > > > + /* True iff no element of T was changed by the substitution. */ > > > > + bool const_subst_p = true; > > > > + > > > > + /* If MAYBE_REUSE is non-NULL, as an optimization we'll try to reuse > > > > and > > > > + return this TREE_VEC instead of allocating a new one if possible. > > > > This > > > > + will either be ARGS or a level from ARGS. */ > > > > + tree maybe_reuse = NULL_TREE; > > > > + > > > > + for (int i = 0; i < len; i++) > > > > { > > > > tree orig_arg = TREE_VEC_ELT (t, i); > > > > tree new_arg; > > > > @@ -13580,56 +13586,90 @@ tsubst_template_args (tree t, tree args, > > > > tsubst_flags_t complain, tree in_decl) > > > > else if (ARGUMENT_PACK_P (orig_arg)) > > > > new_arg = tsubst_argument_pack (orig_arg, args, complain, > > > > in_decl); > > > > else > > > > + { > > > > new_arg = tsubst_template_arg (orig_arg, args, complain, > > > > in_decl); > > > > + /* If T heuristically appears to be a set of generic > > > > template > > > > + arguments, set MAYBE_REUSE to the corresponding level from > > > > + ARGS. */ > > > > + if (maybe_reuse == NULL_TREE && orig_arg != NULL_TREE) > > > > + { > > > > + if (TEMPLATE_PARM_P (orig_arg)) > > > > + { > > > > > > This doesn't handle the case of variadic template parameters, which are > > > represented in the generic args with a pack expansion. If this is a > > > choice, > > > there should be a comment about it. > > > > AFAICT substituting such a pack expansion will never be an identity > > transform -- the relevant targ during tsubst_pack_expansion will be an > > ARGUMENT_PACK, and we'll return the TREE_VEC from that ARGUMENT_PACK > > instead of the ARGUMENT_PACK itself, so there's no way we can reuse (a > > level from) 'args' in this case. > > Hmm, when replacing a level of T... we start with a TREE_VEC containing an > ARGUMENT_PACK around a TREE_VEC containing a PACK_EXPANSION, and substitution > should replace that with the argument level, a TREE_VEC containing an > ARGUMENT_PACK around a TREE_VEC containing an actual set of args, so reuse > ought to be possible? Ah, I think see what you mean. For that, I think it suffices to just handle in tsubst_template_args the case where we're substituting into a single-elt TREE_VEC such as {T...}. That'll allow us to reuse the inner TREE_VEC containing the actual set of args at least. And AFAICT that's the best we can do, since we'll always be creating a new ARGUMENT_PACK which doesn't appear in any other TREE_VEC we have at our disposal. So like this? I also added an assert that 'out' never exceeds 'len', and simplified the test orig_arg && (PACK_EXPANSION_P (orig_arg) || ARGUMENT_PACK_P (orig_arg)) && TREE_CODE (elts[i]) == TREE_VEC to just orig_arg && PACK_EXPANSION_P (orig_arg) && TREE_CODE (elts[i]) == TREE_VEC since substitution into an ARGUMENT_PACK will never yield a TREE_VEC. -- >8 -- Subject: [PATCH] c++: generic targs and identity substitution [PR105956] PR c++/105956 gcc/cp/ChangeLog: * pt.cc (tsubst_template_args): Move variable declarations closer to their first use. Replace 'orig_t' with 'r'. Rename 'need_new' to 'const_subst_p'. Heuristically detect if the substituted elements are identical to that of a level from 'args' and avoid allocating a new TREE_VEC if so. Assert that 'out' doesn't exceed 'len', and remove useless ARGUMENT_PACK_P test. (tsubst_decl) : Revert r13-1045-gcb7fd1ea85feea change for avoiding substitution into DECL_TI_ARGS, but still avoid coercion in this case. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/variadic183.C: New test. --- gcc/cp/pt.cc | 128 +++++++++++++++-------- gcc/testsuite/g++.dg/cpp0x/variadic183.C | 14 +++ 2 files changed, 99 insertions(+), 43 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic183.C diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 8672da123f4..c290174a390 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -27,6 +27,7 @@ along with GCC; see the file COPYING3. If not see Fixed by: C++20 modules. */ #include "config.h" +#define INCLUDE_ALGORITHM // for std::equal #include "system.h" #include "coretypes.h" #include "cp-tree.h" @@ -13544,17 +13545,22 @@ tsubst_argument_pack (tree orig_arg, tree args, tsubst_flags_t complain, tree tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl) { - tree orig_t = t; - int len, need_new = 0, i, expanded_len_adjust = 0, out; - tree *elts; - if (t == error_mark_node) return error_mark_node; - len = TREE_VEC_LENGTH (t); - elts = XALLOCAVEC (tree, len); + const int len = TREE_VEC_LENGTH (t); + tree *elts = XALLOCAVEC (tree, len); + int expanded_len_adjust = 0; - for (i = 0; i < len; i++) + /* True iff the substituted result is identical to T. */ + bool const_subst_p = true; + + /* If MAYBE_REUSE is a TREE_VEC, as an optimization we'll try to reuse and + return this TREE_VEC instead of allocating a new one if possible. This + will either be ARGS or a level from ARGS. */ + tree maybe_reuse = NULL_TREE; + + for (int i = 0; i < len; i++) { tree orig_arg = TREE_VEC_ELT (t, i); tree new_arg; @@ -13580,56 +13586,103 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl) else if (ARGUMENT_PACK_P (orig_arg)) new_arg = tsubst_argument_pack (orig_arg, args, complain, in_decl); else + { new_arg = tsubst_template_arg (orig_arg, args, complain, in_decl); + /* If T heuristically appears to be a set of generic template + arguments, set MAYBE_REUSE to the corresponding level from ARGS. + Otherwise set it to error_mark_node. (Note that this doesn't + handle variadic template parameters, which are represented as a + generic arg by an ARGUMENT_PACK around a one-element TREE_VEC + containing a PACK_EXPANSION. We partially handle that case + later.) */ + if (maybe_reuse == NULL_TREE && orig_arg != NULL_TREE) + { + if (TEMPLATE_PARM_P (orig_arg)) + { + int level, index; + template_parm_level_and_index (orig_arg, &level, &index); + if (index == i && TMPL_ARGS_DEPTH (args) >= level) + maybe_reuse = TMPL_ARGS_LEVEL (args, level); + else + maybe_reuse = error_mark_node; + } + else + maybe_reuse = error_mark_node; + } + } + if (new_arg == error_mark_node) return error_mark_node; elts[i] = new_arg; if (new_arg != orig_arg) - need_new = 1; + const_subst_p = false; } - if (!need_new) + if (const_subst_p) return t; + /* If ARGS and T are both multi-level, the substituted result may be + identical to ARGS (if each level was pairwise identical). */ + if (maybe_reuse == NULL_TREE + && TMPL_ARGS_HAVE_MULTIPLE_LEVELS (t) + && TMPL_ARGS_HAVE_MULTIPLE_LEVELS (args)) + maybe_reuse = args; + + /* Return MAYBE_REUSE and avoid allocating a new TREE_VEC if the substituted + result is identical to it. */ + if (NON_ERROR (maybe_reuse) != NULL_TREE + && TREE_VEC_LENGTH (maybe_reuse) == len + && std::equal (elts, elts+len, TREE_VEC_BEGIN (maybe_reuse))) + return maybe_reuse; + + /* If T consists of only a pack expansion for which substitution resulted + in a TREE_VEC of the expanded elements, then reuse that TREE_VEC instead + of effectively making a copy. */ + if (len == 1 + && PACK_EXPANSION_P (TREE_VEC_ELT (t, 0)) + && TREE_CODE (elts[0]) == TREE_VEC) + return elts[0]; + /* Make space for the expanded arguments coming from template argument packs. */ - t = make_tree_vec (len + expanded_len_adjust); - /* ORIG_T can contain TREE_VECs. That happens if ORIG_T contains the + tree r = make_tree_vec (len + expanded_len_adjust); + /* T can contain TREE_VECs. That happens if T contains the arguments for a member template. - In that case each TREE_VEC in ORIG_T represents a level of template - arguments, and ORIG_T won't carry any non defaulted argument count. + In that case each TREE_VEC in T represents a level of template + arguments, and T won't carry any non defaulted argument count. It will rather be the nested TREE_VECs that will carry one. - In other words, ORIG_T carries a non defaulted argument count only + In other words, T carries a non defaulted argument count only if it doesn't contain any nested TREE_VEC. */ - if (NON_DEFAULT_TEMPLATE_ARGS_COUNT (orig_t)) + if (NON_DEFAULT_TEMPLATE_ARGS_COUNT (t)) { - int count = GET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (orig_t); + int count = GET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (t); count += expanded_len_adjust; - SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (t, count); + SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (r, count); } - for (i = 0, out = 0; i < len; i++) + + int out = 0; + for (int i = 0; i < len; i++) { - tree orig_arg = TREE_VEC_ELT (orig_t, i); + tree orig_arg = TREE_VEC_ELT (t, i); if (orig_arg - && (PACK_EXPANSION_P (orig_arg) || ARGUMENT_PACK_P (orig_arg)) + && PACK_EXPANSION_P (orig_arg) && TREE_CODE (elts[i]) == TREE_VEC) { - int idx; - /* Now expand the template argument pack "in place". */ - for (idx = 0; idx < TREE_VEC_LENGTH (elts[i]); idx++, out++) - TREE_VEC_ELT (t, out) = TREE_VEC_ELT (elts[i], idx); + for (int idx = 0; idx < TREE_VEC_LENGTH (elts[i]); idx++, out++) + TREE_VEC_ELT (r, out) = TREE_VEC_ELT (elts[i], idx); } else { - TREE_VEC_ELT (t, out) = elts[i]; + TREE_VEC_ELT (r, out) = elts[i]; out++; } } + gcc_assert (out <= TREE_VEC_LENGTH (r)); - return t; + return r; } /* Substitute ARGS into one level PARMS of template parameters. */ @@ -14965,32 +15018,21 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain) if (!spec) { - int args_depth = TMPL_ARGS_DEPTH (args); - int parms_depth = TMPL_ARGS_DEPTH (DECL_TI_ARGS (t)); tmpl = DECL_TI_TEMPLATE (t); gen_tmpl = most_general_template (tmpl); - if (args_depth == parms_depth - && !PRIMARY_TEMPLATE_P (gen_tmpl)) - /* The DECL_TI_ARGS in this case are the generic template - arguments for the enclosing class template, so we can - shortcut substitution (which would just be the identity - mapping). */ - argvec = args; - else - { argvec = tsubst (DECL_TI_ARGS (t), args, complain, in_decl); - /* Coerce the innermost arguments again if necessary. If - there's fewer levels of args than of parms, then the - substitution could not have changed the innermost args - (modulo level lowering). */ - if (args_depth >= parms_depth && argvec != error_mark_node) + if (argvec != error_mark_node + && PRIMARY_TEMPLATE_P (gen_tmpl) + && TMPL_ARGS_DEPTH (args) >= TMPL_ARGS_DEPTH (argvec)) + /* We're fully specializing a template declaration, so + we need to coerce the innermost arguments corresponding to + the template. */ argvec = (coerce_innermost_template_parms (DECL_TEMPLATE_PARMS (gen_tmpl), argvec, t, complain, /*all*/true, /*defarg*/true)); if (argvec == error_mark_node) RETURN (error_mark_node); - } hash = spec_hasher::hash (gen_tmpl, argvec); spec = retrieve_specialization (gen_tmpl, argvec, hash); } diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic183.C b/gcc/testsuite/g++.dg/cpp0x/variadic183.C new file mode 100644 index 00000000000..27444ebb594 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/variadic183.C @@ -0,0 +1,14 @@ +// PR c++/105956 +// { dg-do compile { target c++11 } } + +template struct list; + +template struct impl { + static const int idx = 0; + using type = list<(idx + Ns)...>; + + static constexpr const int* a[2] = {(Ns, &idx)...}; + static_assert(a[0] == &idx && a[1] == &idx, ""); +}; + +template struct impl<0, 1>; -- 2.37.0.3.g30cc8d0f14