From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on ip-172-31-74-118.ec2.internal X-Spam-Level: X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.5-pre1 Path: eternal-september.org!reader02.eternal-september.org!aioe.org!5WHqCw2XxjHb2npjM9GYbw.user.gioia.aioe.org.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Performance of records with variant parts Date: Mon, 22 Mar 2021 21:30:56 +0100 Organization: Aioe.org NNTP Server Message-ID: References: <07a56dcc-9e17-49b2-a980-3a5a2d265cedn@googlegroups.com> <3fb9acf6-cf8b-4199-aca8-28d6ff60d63dn@googlegroups.com> NNTP-Posting-Host: 5WHqCw2XxjHb2npjM9GYbw.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 Content-Language: en-US X-Notice: Filtered by postfilter v. 0.9.2 Xref: reader02.eternal-september.org comp.lang.ada:61642 List-Id: On 2021-03-22 19:23, John Perry wrote: > I think I understand that, but the check for "obj.kind" is there in both versions of the code. Isn't that a dynamic check even when I use a non-variant record? What's the difference in the check when I'm checking the discriminant of a variant record and the value of a field? 1. Depending on the optimization level the compiler might keep the second check in place when accessing the variant field regardless the selected case statement alternative. 2. A varying size object might be allocated on the secondary stack rather than on the program stack. That could indict a sufficient penalty 3. Variant alternatives could be allocated outside the object. That would require an additional indirection and thus penalties when copying objects and accessing fields. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de