From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=L6xi=4E=gmail.com=jwakely.gcc@sourceware.org>
Received: from mail-ej1-x630.google.com (mail-ej1-x630.google.com [IPv6:2a00:1450:4864:20::630])
	by sourceware.org (Postfix) with ESMTPS id 5C8A3383B6B5
	for <gcc@gcc.gnu.org>; Tue,  6 Dec 2022 20:37:01 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 5C8A3383B6B5
Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com
Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com
Received: by mail-ej1-x630.google.com with SMTP id x22so9176359ejs.11
        for <gcc@gcc.gnu.org>; Tue, 06 Dec 2022 12:37:01 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20210112;
        h=cc:to:subject:message-id:date:from:in-reply-to:references
         :mime-version:from:to:cc:subject:date:message-id:reply-to;
        bh=aNbSX7Q+iQnpFmX7vqrs+yKhpkkCX8L12jBVYjHp5o0=;
        b=V82q7nI8cHYYWitHEarX6MOe5+NPDmy8pHxnYMY+jK3YQQAtFwe/yy4VcKvGIx9uLF
         93Oxd53OvBYKfL8R8Ic8jKqE2PG5SkjY/Z3ShOoO9DX+gEO/RESEivRbrH0c2QdcMcwv
         m7+ipgtyKTnqs95IaAoPd4w4MgG3AYjrl5LCQ/a5qk/vHHuiHQM+XFnNfyUMLkv8Sstd
         KNAMteh7eTrSt09SsuBMkdOsVHzd60BrhY+JnKvDChFyY1aMVegF3JR5nWjJSZk48Zga
         /pSfDklB+GlDRYhbFkQg7A9xVIk0LroqmI89UaGNw68m6o934IkHsPFFpnGQ0OAAYfEt
         e4dg==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=1e100.net; s=20210112;
        h=cc:to:subject:message-id:date:from:in-reply-to:references
         :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id
         :reply-to;
        bh=aNbSX7Q+iQnpFmX7vqrs+yKhpkkCX8L12jBVYjHp5o0=;
        b=S4mdPTdHLZOAaCblA0JVstPGCqvjm5N20EnoF+a0DWpPPk4aEqA1A370AVH8n7+Bpe
         FP0PVzh8P7dq4PFlikrss5naygTKJ6zruogpZk6iEqMwUyHMA0/+xgx48kRy0cyGHeaT
         0omgLGPtcQkpMCk7/aF+kYMTioOicDM29cgtT7+F9wBUYjqVbrchbcsIgSS5G5OZ0uqx
         ksW+lFFZXyKpSpdHvrrtYegI7Uu8PZLNlCDu1oj0sdcFB5VUVyV/mVFH94qQiYo6mesp
         +7RR1ay5JvVFAJrV7CEA26FttzSrvHdOoUlhmnKwxBGM++KgLFy31rfH/5QLqYTXLtXr
         yGPQ==
X-Gm-Message-State: ANoB5pnOU5+TWrpwxXd6gQGOQiO5D6SAxUrJAsveHaDPyOzOO/Hhwk5r
	c8n27/hDsQu2JJqGJGGQ2KacOvQvnBYjToab3tc=
X-Google-Smtp-Source: AA0mqf6/oRWTW8E5wNBpG6a3leZnKJ+W5JjtPwh6tdEuCOhszGGM3UKam81tDEWd4MZu+DXKWX7TAR5+3QBs2ucZoA0=
X-Received: by 2002:a17:906:518c:b0:7c1:98f:c16a with SMTP id
 y12-20020a170906518c00b007c1098fc16amr4445873ejk.215.1670359020053; Tue, 06
 Dec 2022 12:37:00 -0800 (PST)
MIME-Version: 1.0
References: <CAFtvWZM89spjQ6es3UZsyRNcthZ49TvXUFvwy1cw3qr8qvpfyQ@mail.gmail.com>
 <52ab45bc-cd6e-7acb-dc6f-9cddef4a926a@codesourcery.com> <CAFtvWZNE34=UA5edkPqiq-iU_U5-5MzQn3BceACSe9BYFkRpjA@mail.gmail.com>
 <CAH6eHdRmX72shEPmsX2ajB7uU16svwkXUGc-6jiVRZbOwxm85A@mail.gmail.com> <CAFtvWZMxmeeZY8QpODgTQmvBRAR62hDaqwN6D2XCvnY8JmFikw@mail.gmail.com>
In-Reply-To: <CAFtvWZMxmeeZY8QpODgTQmvBRAR62hDaqwN6D2XCvnY8JmFikw@mail.gmail.com>
From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Tue, 6 Dec 2022 20:36:46 +0000
Message-ID: <CAH6eHdRukNcPpYudPGq19XXZQfg7W0-n-V_i9fctVxKnU+uMHg@mail.gmail.com>
Subject: Re: Using [[may_alias]] in C23/C++23 on a union works in neither
 post-"union" position, or at the end of the definition
To: Gavin Ray <ray.gavin97@gmail.com>
Cc: Joseph Myers <joseph@codesourcery.com>, "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Content-Type: text/plain; charset="UTF-8"
X-Spam-Status: No, score=-0.6 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,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: <gcc.gcc.gnu.org>

On Tue, 6 Dec 2022 at 20:32, Gavin Ray wrote:
>
> Ah got it, didn't know that (handy, will save me duplicating a bunch of attributes).
> Thanks Jonathan!

The Clang doc acually show all the forms that can be used for each attribute:

https://clang.llvm.org/docs/AttributeReference.html#may-alias

"GNU" means __attribute__((may_alias)) and the C++11 and C2x columns
show that [[gnu::may_alias]] is the right way to use it.

Clang-specific attributes use clang:: instead e.g.
https://clang.llvm.org/docs/AttributeReference.html#preserve-all