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* [Bug c++/110312] New: -Wcast-align=strict warning despite alignas
@ 2023-06-19 14:40 f.heckenbach@fh-soft.de
2023-06-19 17:20 ` [Bug c++/110312] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: f.heckenbach@fh-soft.de @ 2023-06-19 14:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110312
Bug ID: 110312
Summary: -Wcast-align=strict warning despite alignas
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: f.heckenbach@fh-soft.de
Target Milestone: ---
% cat test.cpp
alignas (int) char a[sizeof (int)];
auto b = reinterpret_cast <int &> (a);
% g++ -c -Wcast-align=strict test.cpp
test.cpp:2:10: warning: cast from 'char (*)[4]' to 'int*' increases required
alignment of target type [-Wcast-align]
I'd kind of understand the warning if I was casting &a to int* because the
alignas information might get lost when taking the address. So I tried casting
a reference, but apparently (telling from the message), gcc implements this via
a pointer cast anyway, so it doesn't help.
FWIW, I got this when I tried to replace aligned_storage_t (which is deprecated
in C++23 for reasons I don't really understand TBH) with a std::byte array as
suggested. Does this mean that I simply can't use -Wcast-align=strict then?
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/110312] -Wcast-align=strict warning despite alignas
2023-06-19 14:40 [Bug c++/110312] New: -Wcast-align=strict warning despite alignas f.heckenbach@fh-soft.de
@ 2023-06-19 17:20 ` pinskia at gcc dot gnu.org
2023-06-19 17:33 ` f.heckenbach@fh-soft.de
2023-06-20 8:10 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-06-19 17:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110312
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The decl has the increased alignment but the type does not in this case.
So I think the warning is still correct.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/110312] -Wcast-align=strict warning despite alignas
2023-06-19 14:40 [Bug c++/110312] New: -Wcast-align=strict warning despite alignas f.heckenbach@fh-soft.de
2023-06-19 17:20 ` [Bug c++/110312] " pinskia at gcc dot gnu.org
@ 2023-06-19 17:33 ` f.heckenbach@fh-soft.de
2023-06-20 8:10 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: f.heckenbach@fh-soft.de @ 2023-06-19 17:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110312
--- Comment #2 from Frank Heckenbach <f.heckenbach@fh-soft.de> ---
(In reply to Andrew Pinski from comment #1)
> The decl has the increased alignment but the type does not in this case.
>
> So I think the warning is still correct.
So there's no way around it other then disabling the warning, correct?
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/110312] -Wcast-align=strict warning despite alignas
2023-06-19 14:40 [Bug c++/110312] New: -Wcast-align=strict warning despite alignas f.heckenbach@fh-soft.de
2023-06-19 17:20 ` [Bug c++/110312] " pinskia at gcc dot gnu.org
2023-06-19 17:33 ` f.heckenbach@fh-soft.de
@ 2023-06-20 8:10 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-06-20 8:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110312
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2023-06-20
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think the warning isn't useful at least, maybe it can be improved to not
diagnose in the case where we can see an appropriately aligned decl (with some
effort).
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-06-20 8:10 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2023-06-19 14:40 [Bug c++/110312] New: -Wcast-align=strict warning despite alignas f.heckenbach@fh-soft.de
2023-06-19 17:20 ` [Bug c++/110312] " pinskia at gcc dot gnu.org
2023-06-19 17:33 ` f.heckenbach@fh-soft.de
2023-06-20 8:10 ` rguenth at gcc dot gnu.org
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