From: Jason Merrill <jason@redhat.com>
To: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Richard Biener <rguenther@suse.de>,
Jakub Jelinek <jakub@redhat.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Marc Glisse <marc.glisse@inria.fr>,
Jonathan Wakely <jwakely@redhat.com>, Jeff Law <law@redhat.com>
Subject: Re: [PATCH] Add a new type attribute always_alias (PR79671)
Date: Wed, 05 Apr 2017 20:18:00 -0000 [thread overview]
Message-ID: <CADzB+2kGSL=yLDARcrXW2cAafEZC2Q84kTd0tjyALrLiRpqTRg@mail.gmail.com> (raw)
In-Reply-To: <AM4PR0701MB21627566C67EB9B4CB0F501FE40A0@AM4PR0701MB2162.eurprd07.prod.outlook.com>
On Wed, Apr 5, 2017 at 1:41 PM, Bernd Edlinger
<bernd.edlinger@hotmail.de> wrote:
> On 04/05/17 17:20, Richard Biener wrote:
>>> Also, wonder if you need to mark all types containing such arrays,
>>> if you couldn't just set that flag in C++ on unsigned char/std::byte
>>> arrays (and on anything with that attribute), have that imply alias set
>>> 0 on it and then let the rest of alias machinery handle aggregate types
>>> containing such fields.
>>
>> Yes, I expected it to work like this (didn't look at the patch yet).
My impression is that this is how GCC 6 worked, but GCC 7 decides to
ignore alias set 0 members. Is that right?
> I want to allow *only* what the C++ standard requires or what Jason says
> of course :), and not a single bit more, because it suppresses otherwise
> correct optimizations.
>
> So a struct with a std::byte member is not alias_set 0,
> only the std::byte itself is, but an array of std::byte
> is itself typeless_storage, and makes the whole structure
> also typeless_storage
Well, only the array member, not the whole structure, but it may make
sense for GCC to treat the whole structure as such internally.
Jason
next prev parent reply other threads:[~2017-04-05 20:18 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-05 9:46 Bernd Edlinger
2017-04-05 13:28 ` Jakub Jelinek
2017-04-05 15:20 ` Richard Biener
2017-04-05 17:41 ` Bernd Edlinger
2017-04-05 20:18 ` Jason Merrill [this message]
2017-04-05 20:46 ` Bernd Edlinger
2017-04-05 22:54 ` Pedro Alves
2017-04-06 10:08 ` Jonathan Wakely
2017-04-06 7:23 ` Richard Biener
2017-04-05 15:27 ` Bernd Edlinger
2017-04-05 15:29 ` Jakub Jelinek
2017-04-05 14:50 ` Florian Weimer
2017-04-05 15:23 ` Richard Biener
2017-04-05 15:38 ` Bernd Edlinger
2017-04-05 16:03 ` Jonathan Wakely
2017-04-05 16:08 ` Jakub Jelinek
2017-04-05 17:23 ` Bernd Edlinger
2017-04-05 21:02 ` Bernd Edlinger
2017-04-05 23:17 ` Sandra Loosemore
2017-04-06 5:40 ` Jakub Jelinek
2017-04-06 7:47 ` Richard Biener
2017-04-06 7:51 ` Jakub Jelinek
2017-04-06 7:55 ` Richard Biener
2017-04-06 14:11 ` Bernd Edlinger
2017-04-06 14:17 ` Florian Weimer
2017-04-06 14:23 ` Richard Biener
2017-04-06 14:43 ` Jonathan Wakely
2017-04-06 14:51 ` Florian Weimer
2017-04-06 15:05 ` Jakub Jelinek
2017-04-06 15:10 ` Florian Weimer
2017-04-06 19:13 ` Richard Biener
2017-04-11 10:43 ` Florian Weimer
2017-04-11 10:48 ` Richard Biener
2017-04-06 17:39 ` Bernd Edlinger
2017-04-06 17:48 ` Florian Weimer
2017-04-06 18:12 ` Bernd Edlinger
2017-04-06 18:19 ` Florian Weimer
2017-04-06 18:49 ` Bernd Edlinger
2017-04-06 19:05 ` Florian Weimer
2017-04-06 19:20 ` Bernd Edlinger
2017-04-07 6:47 ` Richard Biener
2017-04-07 12:58 ` Bernd Edlinger
2017-04-06 19:16 ` Richard Biener
2017-04-07 6:56 ` Florian Weimer
2017-04-07 8:01 ` Richard Biener
2017-04-06 19:14 ` Richard Biener
2017-04-06 19:51 ` Bernd Edlinger
2017-04-06 14:22 ` Richard Biener
2017-04-06 21:00 ` Bernd Edlinger
2017-04-07 6:54 ` Richard Biener
2017-04-07 13:37 ` Bernd Edlinger
2017-04-07 15:10 ` Richard Biener
2017-04-07 15:33 ` Bernd Edlinger
2017-04-07 20:22 ` Jason Merrill
2017-04-10 12:50 ` Richard Biener
2017-04-10 14:41 ` Jason Merrill
2017-04-10 15:31 ` Richard Biener
2017-04-10 16:35 ` Jason Merrill
2017-04-11 10:32 ` Richard Biener
2017-04-11 11:53 ` Richard Biener
2017-04-11 13:35 ` Richard Biener
2017-04-11 18:47 ` Jason Merrill
2017-04-10 21:40 ` Pedro Alves
2017-04-11 7:37 ` Richard Biener
2017-04-06 20:20 ` Bernd Edlinger
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