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{ "id": 2226257, "url": "http://patchwork.ozlabs.org/api/1.1/covers/2226257/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/cover/bmm.hhub9plyek.gcc.gcc-TEST.redi.16.1.0@forge-stage.sourceware.org/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/1.1/projects/17/?format=api", "name": "GNU Compiler Collection", "link_name": "gcc", "list_id": "gcc-patches.gcc.gnu.org", "list_email": "gcc-patches@gcc.gnu.org", "web_url": null, "scm_url": null, "webscm_url": null }, "msgid": "<bmm.hhub9plyek.gcc.gcc-TEST.redi.16.1.0@forge-stage.sourceware.org>", "date": "2026-04-22T10:26:25", "name": "[v1,0/1] libstdc++: Refactor std::hash specializations", "submitter": { "id": 93210, "url": "http://patchwork.ozlabs.org/api/1.1/people/93210/?format=api", "name": "Jonathan Wakely via Sourceware Forge", "email": "forge-bot+redi@forge-stage.sourceware.org" }, "mbox": "http://patchwork.ozlabs.org/project/gcc/cover/bmm.hhub9plyek.gcc.gcc-TEST.redi.16.1.0@forge-stage.sourceware.org/mbox/", "series": [ { "id": 500974, "url": "http://patchwork.ozlabs.org/api/1.1/series/500974/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=500974", "date": "2026-04-22T10:26:26", "name": "libstdc++: Refactor std::hash specializations", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/500974/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/covers/2226257/comments/", "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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Wed, 22 Apr 2026 10:27:19 +0000 (GMT)", "from forge-stage.sourceware.org (localhost [IPv6:::1])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange x25519 server-signature ECDSA (prime256v1) server-digest SHA256)\n (No client certificate requested)\n by forge-stage.sourceware.org (Postfix) with ESMTPS id 10CC6405A9\n for <gcc-patches@gcc.gnu.org>; Wed, 22 Apr 2026 10:27:19 +0000 (UTC)" ], "DKIM-Filter": [ "OpenDKIM Filter v2.11.0 sourceware.org D0C1B4335881", "OpenDKIM Filter v2.11.0 sourceware.org 3A5AE4B920DB" ], "DMARC-Filter": "OpenDMARC Filter v1.4.2 sourceware.org 3A5AE4B920DB", "ARC-Filter": "OpenARC Filter v1.0.0 sourceware.org 3A5AE4B920DB", "ARC-Seal": "i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1776853639; cv=none;\n b=rSEEo5UbkH8tAWSusipzysR6895Qcrdq/LTGhSkKQL/c5ejqnJZIjPqt2he7OKucNWUCIXKtgzgu1m5BcfK+dpuIWfAZ1IyLzrm6VO6OxdGpStRJpm5iLE9+bRQQSn1zY5hRP2ydM9PVW/yIyWO4GKhQc36OgAo/ORUrPPhW3ZU=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1776853639; c=relaxed/simple;\n bh=JMIRLLH7kteBua8F1eMeW1JUQjADsksD1ua7YjLAxcQ=;\n h=From:Date:Subject:To:Message-ID;\n b=k0p//zXzlU/sOsNM6tBCQyrV52M0bD3qLrMDzdaLqiYYSJPTwKYjBNyy8TEnhhJ9HL8sggnO2t3tJt6aEve1CAySbGBUVcxmxTRLRBHeaMCxz9/DYAEuyNgSn6aNRv1e8b9eoVB+XNfWNxiFqKLkzTmwEh3J7PiB2TTkkETXxJc=", "ARC-Authentication-Results": "i=1; server2.sourceware.org", "From": "Jonathan Wakely via Sourceware Forge\n <forge-bot+redi@forge-stage.sourceware.org>", "Date": "Wed, 22 Apr 2026 10:26:25 +0000", "Subject": "[PATCH v1 0/1] libstdc++: Refactor std::hash specializations", "To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>", "Message-ID": "\n <bmm.hhub9plyek.gcc.gcc-TEST.redi.16.1.0@forge-stage.sourceware.org>", "X-Mailer": "batrachomyomachia", "X-Pull-Request-Organization": "gcc", "X-Pull-Request-Repository": "gcc-TEST", "X-Pull-Request": "https://forge.sourceware.org/gcc/gcc-TEST/pulls/16", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Reply-To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>, redi@gcc.gnu.org", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "Hi gcc-patches mailing list,\nJonathan Wakely via Sourceware Forge <forge-bot+redi@forge-stage.sourceware.org> has requested that the following forgejo pull request\nbe published on the mailing list.\n\nCreated on: 2024-11-06 15:46:39+00:00\nLatest update: 2025-12-16 09:30:48+00:00\nChanges: 0 changed files, 0 additions, 0 deletions\nHead revision: redi/gcc ref refs/pull/16/head commit 34be1a8927df3aad5db13394a813c60dd83c4e14\nBase revision: gcc/gcc-TEST ref trunk commit 85736ba8e1fc4a5003f958dd268a155e379e059f r15-4983-g85736ba8e1fc4a\nMerge base: 85736ba8e1fc4a5003f958dd268a155e379e059f\nFull diff url: https://forge.sourceware.org/gcc/gcc-TEST/pulls/16.diff\nDiscussion: https://forge.sourceware.org/gcc/gcc-TEST/pulls/16\nRequested Reviewers:\n\nThis attempts to simplify and clean up our std::hash code. The primary\nbenefit is improved diagnostics for users when they do something wrong\ninvolving std::hash or unordered containers. An additional benefit is\nthat for the unstable ABI (--enable-symvers=gnu-versioned-namespace) we\ncan reduce the memory footprint of several std::hash specializations.\n\nIn the current design, __hash_enum is a base class of the std::hash\nprimary template, but the partial specialization of __hash_enum for\nnon-enum types is disabled. This means that if a user forgets to\nspecialize std::hash for their class type (or forgets to use a custom\nhash function for unordered containers) they get error messages about\nstd::__hash_enum not being constructible. This is confusing when there\nis no enum type involved: why should users care about __hash_enum not\nbeing constructible if they're not trying to hash enums?\n\nThis change makes the std::hash primary template only derive from\n__hash_enum when the template argument type is an enum. Otherwise, it\nderives directly from a new class template, __hash_not_enabled. This new\nclass template defines the deleted members that cause a given std::hash\nspecialization to be a disabled specialization (as per P0513R0). Now\nwhen users try to use a disabled specialization, they get more\ndescriptive errors that mention __hash_not_enabled instead of\n__hash_enum.\n\nAdditionally, adjust __hash_base to remove the deprecated result_type\nand argument_type typedefs for C++20 and later.\n\nIn the current code we use a __poison_hash base class in the std::hash\nspecializations for std::unique_ptr, std::optional, and std::variant.\nThe primary template of __poison_hash has deleted special members, which\nis used to conditionally disable the derived std::hash specialization.\nThis can also result in confusing diagnostics, because seeing \"poison\"\nin an enabled specialization is misleading. Only some uses of\n__poison_hash actually \"poison\" anything, i.e. cause a specialization to\nbe disabled. In other cases it's just an empty base class that does\nnothing.\n\nThis change removes __poison_hash and changes the std::hash\nspecializations that were using it to conditionally derive from\n__hash_not_enabled instead. When the std::hash specialization is\nenabled, there is no more __poison_hash base class. However, to preserve\nthe ABI properties of those std::hash specializations, we need to\nreplace __poison_hash with some other empty base class. This is needed\nbecause in the current code std::hash<std::variant<int, const int>> has\ntwo __poison_hash<int> base classes, which must have unique addresses,\nso sizeof(std::hash<std::variant<int, const int>>) == 2. To preserve\nthis unfortunate property, a new __hash_empty_base class is used as a\nbase class to re-introduce du0plicate base classes that increase the\nclass size. For the unstable ABI we don't use __hash_empty_base so the\nstd::hash<std::variant<T...>> specializations are always size 1, and\nthe class hierarchy is much simpler so will compile faster.\n\nAdditionally, remove the result_type and argument_type typedefs from all\ndisabled specializations of std::hash for std::unique_ptr,\nstd::optional, and std::variant. Those typedefs are useless for disabled\nspecializations, and although the standard doesn't say they must *not*\nbe present for disabled specializations, it certainly only requires them\nfor enabled specializations. Finally, for C++20 the typedefs are also\nremoved from enabled specializations of std::hash for std::unique_ptr,\nstd::optional, and std::variant.\n\n```\nlibstdc++-v3/ChangeLog:\n\n\t* doc/xml/manual/evolution.xml: Document removal of nested types\n\tfrom std::hash specializations.\n\t* doc/html/manual/api.html: Regenerate.\n\t* include/bits/functional_hash.h (__hash_base): Remove\n\tdeprecated nested types for C++20.\n\t(__hash_empty_base): Define new class template.\n\t(__is_hash_enabled_for): Define new variable template.\n\t(__poison_hash): Remove.\n\t(__hash_not_enabled): Define new class template.\n\t(__hash_enum): Remove partial specialization for non-enums.\n\t(hash): Derive from __hash_not_enabled for non-enums, instead of\n\t__hash_enum.\n\t* include/bits/unique_ptr.h (__uniq_ptr_hash): Derive from\n\t__hash_base. Conditionally derive from __hash_empty_base.\n\t(__uniq_ptr_hash<>): Remove disabled specialization.\n\t(hash): Do not derive from __hash_base unconditionally.\n\tConditionally derive from either __uniq_ptr_hash or\n\t__hash_not_enabled.\n\t* include/std/optional (__optional_hash_call_base): Remove.\n\t(__optional_hash): Define new class template.\n\t(hash): Derive from either\n\t(hash): Conditionally derive from either __optional_hash or\n\t__hash_not_enabled. Remove nested typedefs.\n\t* include/std/variant (_Base_dedup): Replace __poison_hash with\n\t__hash_empty_base.\n\t(__variant_hash_call_base_impl): Remove.\n\t(__variant_hash): Define new class template.\n\t(hash): Conditionally derive from either __variant_hash or\n\t__hash_not_enabled. Remove nested typedefs.\n\t* testsuite/20_util/optional/hash.cc: Check whether nested types\n\tare present.\n\t* testsuite/20_util/variant/hash.cc: Likewise.\n\t* testsuite/20_util/optional/hash_abi.cc: New test.\n\t* testsuite/20_util/unique_ptr/hash/abi.cc: New test.\n\t* testsuite/20_util/unique_ptr/hash/types.cc: New test.\n\t* testsuite/20_util/variant/hash_abi.cc: New test.\n```\n\n\nChanged files:\n- A: libstdc++-v3/testsuite/20_util/optional/hash_abi.cc\n- A: libstdc++-v3/testsuite/20_util/unique_ptr/hash/abi.cc\n- A: libstdc++-v3/testsuite/20_util/unique_ptr/hash/types.cc\n- A: libstdc++-v3/testsuite/20_util/variant/hash_abi.cc\n- M: libstdc++-v3/doc/html/manual/api.html\n- M: libstdc++-v3/doc/xml/manual/evolution.xml\n- M: libstdc++-v3/include/bits/functional_hash.h\n- M: libstdc++-v3/include/bits/unique_ptr.h\n- M: libstdc++-v3/include/std/optional\n- M: libstdc++-v3/include/std/variant\n- M: libstdc++-v3/testsuite/20_util/optional/hash.cc\n- M: libstdc++-v3/testsuite/20_util/variant/hash.cc\n\n\nJonathan Wakely (1):\n libstdc++: Refactor std::hash specializations\n\n libstdc++-v3/doc/html/manual/api.html | 3 +\n libstdc++-v3/doc/xml/manual/evolution.xml | 5 ++\n libstdc++-v3/include/bits/functional_hash.h | 47 +++++++-------\n libstdc++-v3/include/bits/unique_ptr.h | 18 +++---\n libstdc++-v3/include/std/optional | 26 ++++----\n libstdc++-v3/include/std/variant | 41 ++++++------\n .../testsuite/20_util/optional/hash.cc | 33 ++++++++++\n .../testsuite/20_util/optional/hash_abi.cc | 35 ++++++++++\n .../testsuite/20_util/unique_ptr/hash/abi.cc | 64 +++++++++++++++++++\n .../20_util/unique_ptr/hash/types.cc | 53 +++++++++++++++\n .../testsuite/20_util/variant/hash.cc | 34 ++++++++++\n .../testsuite/20_util/variant/hash_abi.cc | 48 ++++++++++++++\n 12 files changed, 344 insertions(+), 63 deletions(-)\n create mode 100644 libstdc++-v3/testsuite/20_util/optional/hash_abi.cc\n create mode 100644 libstdc++-v3/testsuite/20_util/unique_ptr/hash/abi.cc\n create mode 100644 libstdc++-v3/testsuite/20_util/unique_ptr/hash/types.cc\n create mode 100644 libstdc++-v3/testsuite/20_util/variant/hash_abi.cc" }