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From: "andrew2085 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/95349] Using std::launder(p) produces unexpected behavior where (p) produces expected behavior
Date: Tue, 02 Jun 2020 20:53:29 +0000	[thread overview]
Message-ID: <bug-95349-4-vMMtl1nxa8@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-95349-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95349

--- Comment #29 from Andrew Downing <andrew2085 at gmail dot com> ---
So I think this sort of equivalent example in C shows what's going wrong in the
C++ example. https://godbolt.org/z/ZMz4Cp

gcc knows that if the object mem points to is modified inside pun() its
effective type will change to the type of the value that is assigned because
the object mem points to has no declared type. If the argument to pun has a
declared type, the code doesn't work, like in the c++ example.

So for this c++ example https://godbolt.org/z/NeAJ5d could a solution be for
gcc to treat placement new as if it were a modifying access and as if it's
parameter had no declared type. So it would change the effective type of d in
f1 to uint64_t, or at least insert IL instructions to simulate that?

  parent reply	other threads:[~2020-06-02 20:53 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-26 20:45 [Bug c++/95349] New: " andrew2085 at gmail dot com
2020-05-27  8:04 ` [Bug c++/95349] " rguenth at gcc dot gnu.org
2020-05-27  9:14 ` redi at gcc dot gnu.org
2020-05-27  9:40 ` rguenther at suse dot de
2020-05-27 11:05 ` redi at gcc dot gnu.org
2020-05-27 14:45 ` andrew2085 at gmail dot com
2020-05-27 15:07 ` redi at gcc dot gnu.org
2020-05-27 15:19 ` andrew2085 at gmail dot com
2020-05-27 16:01 ` andrew2085 at gmail dot com
2020-05-29 10:59 ` ed at catmur dot uk
2020-05-29 11:23 ` rguenth at gcc dot gnu.org
2020-05-29 11:32 ` rguenth at gcc dot gnu.org
2020-05-29 13:53 ` ed at catmur dot uk
2020-05-29 14:15 ` redi at gcc dot gnu.org
2020-05-29 14:24 ` rguenther at suse dot de
2020-05-29 15:05 ` andrew2085 at gmail dot com
2020-05-29 18:07 ` richard-gccbugzilla at metafoo dot co.uk
2020-05-29 21:00 ` andrew2085 at gmail dot com
2020-05-29 21:50 ` richard-gccbugzilla at metafoo dot co.uk
2020-05-29 23:13 ` andrew2085 at gmail dot com
2020-05-29 23:25 ` richard-gccbugzilla at metafoo dot co.uk
2020-06-02 12:09 ` rguenth at gcc dot gnu.org
2020-06-02 12:20 ` rguenth at gcc dot gnu.org
2020-06-02 16:00 ` andrew2085 at gmail dot com
2020-06-02 16:23 ` rguenther at suse dot de
2020-06-02 16:34 ` andrew2085 at gmail dot com
2020-06-02 16:37 ` andrew2085 at gmail dot com
2020-06-02 17:54 ` rguenther at suse dot de
2020-06-02 18:43 ` andrew2085 at gmail dot com
2020-06-02 20:53 ` andrew2085 at gmail dot com [this message]
2020-06-03  6:52 ` rguenth at gcc dot gnu.org
2020-06-04  0:27 ` andrew2085 at gmail dot com
2020-06-04  6:14 ` rguenther at suse dot de
2020-06-04 16:05 ` andrew2085 at gmail dot com
2020-06-05  6:52 ` rguenth at gcc dot gnu.org
2020-06-05 14:30 ` andrew2085 at gmail dot com
2020-06-15  9:29 ` rguenth at gcc dot gnu.org
2020-06-15 21:45 ` richard-gccbugzilla at metafoo dot co.uk
2020-06-16  3:27 ` andrew2085 at gmail dot com
2020-06-16  6:50 ` rguenther at suse dot de
2020-06-16  6:57 ` rguenther at suse dot de
2020-06-16 13:56 ` andrew2085 at gmail dot com
2022-01-11 12:43 ` rguenth at gcc dot gnu.org
2022-01-11 12:48 ` rguenth at gcc dot gnu.org
2022-11-14  4:53 ` andrew2085 at gmail dot com
2024-06-03  8:02 ` Christopher.Nerz at de dot bosch.com
2024-06-03  8:51 ` rguenth at gcc dot gnu.org
2024-06-03  9:13 ` Christopher.Nerz at de dot bosch.com
2024-06-03  9:23 ` rguenth at gcc dot gnu.org
2024-06-03 10:26 ` Christopher.Nerz at de dot bosch.com
2024-06-03 11:19 ` rguenther at suse dot de
2024-06-03 15:53 ` redi at gcc dot gnu.org
2024-06-03 16:00 ` redi at gcc dot gnu.org

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