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Sun, 10 Dec 2023 10:22:43 +0000 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Richard Biener Mime-Version: 1.0 (1.0) Subject: Re: [PATCH] c++: End lifetime of objects in constexpr after destructor call [PR71093] Date: Sun, 10 Dec 2023 11:22:28 +0100 Message-Id: References: Cc: Nathaniel Shead , gcc-patches@gcc.gnu.org In-Reply-To: To: Jason Merrill X-Mailer: iPhone Mail (21B101) X-Spam-Score: 3.08 Authentication-Results: smtp-out1.suse.de; none X-Spam-Score: 2.38 X-Spamd-Result: default: False [2.38 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; BAYES_HAM(-0.00)[43.96%]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; MV_CASE(0.50)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MIME_GOOD(-0.10)[text/plain]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-0.999]; TO_DN_SOME(0.00)[]; NEURAL_SPAM_SHORT(2.98)[0.995]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_CC(0.00)[gmail.com,gcc.gnu.org]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[] X-Spam-Flag: NO X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS,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 List-Id: > Am 09.12.2023 um 21:13 schrieb Jason Merrill : >=20 > =EF=BB=BFOn 11/2/23 21:18, Nathaniel Shead wrote: >> Bootstrapped and regtested on x86-64_pc_linux_gnu. >> I'm not entirely sure if the change I made to have destructors clobber wi= th >> CLOBBER_EOL instead of CLOBBER_UNDEF is appropriate, but nothing seemed t= o have >> broken by doing this and I wasn't able to find anything else that really >> depended on this distinction other than a warning pass. Otherwise I could= >> experiment with a new clobber kind for destructor calls. >=20 > It seems wrong to me: CLOBBER_EOL is documented to mean that the storage i= s expiring at that point as well, which a (pseudo-)destructor does not imply= ; it's perfectly valid to destroy an object and then create another in the s= ame storage. >=20 > We probably do want another clobber kind for end of object lifetime. And/o= r one for beginning of object lifetime. There=E2=80=99s not much semantically different between UNDEF and end of obj= ect but not storage lifetime? At least for what middle-end optimizations do= . EOL is used by stack slot sharing and that operates on the underlying storag= e, not individual objects live in it. Richard=20 > Jason >=20