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* [Bug c++/99841] New: (temporary) refs
@ 2021-03-30 19:38 g.peterhoff@t-online.de
2021-03-30 19:49 ` [Bug c++/99841] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: g.peterhoff@t-online.de @ 2021-03-30 19:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99841
Bug ID: 99841
Summary: (temporary) refs
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: g.peterhoff@t-online.de
Target Milestone: ---
please see https://godbolt.org/z/Ez1K7eofr
gcc gives different (false?) results than clang/icc. If you set O0 or remove
O-option gives same results.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/99841] (temporary) refs
2021-03-30 19:38 [Bug c++/99841] New: (temporary) refs g.peterhoff@t-online.de
@ 2021-03-30 19:49 ` pinskia at gcc dot gnu.org
2021-03-30 20:00 ` g.peterhoff@t-online.de
2021-03-30 20:09 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-03-30 19:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99841
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The question is:
mm_pair_t<type> m{type(1), type(2)};
I think GCC is correct here, type(1) is a temp and it does not bind to a field
directly, it goes through a constructure and therefor the temp goes away right
after the statement is done.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/99841] (temporary) refs
2021-03-30 19:38 [Bug c++/99841] New: (temporary) refs g.peterhoff@t-online.de
2021-03-30 19:49 ` [Bug c++/99841] " pinskia at gcc dot gnu.org
@ 2021-03-30 20:00 ` g.peterhoff@t-online.de
2021-03-30 20:09 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: g.peterhoff@t-online.de @ 2021-03-30 20:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99841
--- Comment #2 from g.peterhoff@t-online.de ---
That is not the problem. I only made using type = ... and type(x) in the ctor
calls so that I can test different types. You like to throw that out - has no
influence.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/99841] (temporary) refs
2021-03-30 19:38 [Bug c++/99841] New: (temporary) refs g.peterhoff@t-online.de
2021-03-30 19:49 ` [Bug c++/99841] " pinskia at gcc dot gnu.org
2021-03-30 20:00 ` g.peterhoff@t-online.de
@ 2021-03-30 20:09 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-03-30 20:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99841
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to g.peterhoff from comment #2)
> That is not the problem. I only made using type = ... and type(x) in the
> ctor calls so that I can test different types. You like to throw that out -
> has no influence.
I think you misunderstood.
Take a look at:
mm_pair_t<type> m{type(1), type(2)};
there are two temps here created by type(1) and type(2). The lifetime of those
temps normally end at the end of the statement, unless they are extended due to
the C++ rules of binding the temp to a reference. In this case they are not
bound to a reference as the reference is not m but rather the constructor
arguments (this is why mm_t works while the others don't).
Adding -W -Wall -Werror to the command line we get the following
warnings/errors:
<source>: In function 'int main()':
<source>:33:24: error: '<anonymous>' is used uninitialized
[-Werror=uninitialized]
33 | std::cout << m.first << std::endl;
| ^~~~~
<source>:34:24: error: '<anonymous>' is used uninitialized
[-Werror=uninitialized]
34 | std::cout << m.second << std::endl;
| ^~~~~~
<source>:39:35: error: '<anonymous>' is used uninitialized
[-Werror=uninitialized]
39 | std::cout << std::get<0>(m) << std::endl;
| ^
<source>:40:35: error: '<anonymous>' is used uninitialized
[-Werror=uninitialized]
40 | std::cout << std::get<1>(m) << std::endl;
| ^
<source>:45:24: error: '<anonymous>' is used uninitialized
[-Werror=uninitialized]
45 | std::cout << m.min << std::endl;
| ^~~
<source>:46:24: error: '<anonymous>' is used uninitialized
[-Werror=uninitialized]
46 | std::cout << m.max << std::endl;
| ^~~
----- CUT ----
Which is exactly what you expect when the temp rvalue does not gets its
timeline extended past the end of that statement.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-03-30 19:38 [Bug c++/99841] New: (temporary) refs g.peterhoff@t-online.de
2021-03-30 19:49 ` [Bug c++/99841] " pinskia at gcc dot gnu.org
2021-03-30 20:00 ` g.peterhoff@t-online.de
2021-03-30 20:09 ` pinskia at gcc dot gnu.org
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