* [Bug c++/64372] Spurious warning with throw in ternary operator returning const reference
2014-12-21 18:43 [Bug c++/64372] New: Spurious warning with throw in ternary operator returning const reference tavianator at gmail dot com
@ 2014-12-22 0:49 ` manu at gcc dot gnu.org
2014-12-22 7:31 ` harald at gigawatt dot nl
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: manu at gcc dot gnu.org @ 2014-12-22 0:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64372
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |glisse at gcc dot gnu.org,
| |manu at gcc dot gnu.org
Known to fail| |4.9.2, 5.0
--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
I think *p creates a temporary that only lasts until the end of the function,
so the code is undefined. Probably even:
const char&
foz(const char* p)
{
return *p;
}
is undefined. However, G++ and Clang currently handles this as returning p:
;; Function const char& foz(const char*) (null)
;; enabled by -tree-original
return <retval> = (const char &) NON_LVALUE_EXPR <p>;
;; Function const char& foo(const char*, const char*) (null)
;; enabled by -tree-original
return <retval> = (const char &) (p != 0B ? NON_LVALUE_EXPR <p> :
NON_LVALUE_EXPR <q>);
;; Function const char& fzz(const char*) (null)
;; enabled by -tree-original
<<cleanup_point return <retval> = (const char &) &TARGET_EXPR <D.2338, p != 0B
? (char) *p : <<< Unknown tree: throw_expr
<<cleanup_point TARGET_EXPR <D.2335, __cxa_allocate_exception (8)>;, *(const
char * *) D.2335 = p;>>;, __cxa_throw (D.2335, (void *) &_ZTIPKc, 0B); >>>>;,
0>>;
Note that in the testcase that throws, the gimple indicates that the reference
is set to null even when not throwing, which leads to a segmentation fault.
const char& fzz(const char*) (const char * p)
{
const charD.10 & D.2348;
const charD.10 D.2338;
charD.10 iftmp.1D.2349;
voidD.45 * D.2335;
[test.cc:18:24] if (pD.2330 != 0B) goto <D.2350>; else goto <D.2351>;
<D.2350>:
[test.cc:18:24] iftmp.1D.2349 = [test.cc:18:24] *pD.2330;
goto <D.2352>;
<D.2351>:
[test.cc:18:24] # USE = anything
# CLB = anything
D.2335 = __cxa_allocate_exceptionD.2334 (8);
[test.cc:18:24] try
{
[test.cc:18:24] [test.cc:18:24] MEM[(const charD.10 * *)D.2335] =
pD.2330;
}
catch
{
[test.cc:18:24] # USE = anything
# CLB = anything
__cxa_free_exceptionD.2336 (D.2335);
}
[test.cc:18:24] # USE = anything
# CLB = anything
__cxa_throwD.2333 (D.2335, &_ZTIPKcD.2337, 0B);
<D.2352>:
[test.cc:18:24] D.2338 = iftmp.1D.2349;
[test.cc:18:24] try
{
[test.cc:18:24] D.2348 = 0;
[test.cc:18:24] return D.2348;
}
finally
{
[test.cc:18:24] D.2338 = {CLOBBER};
}
}
>From gcc-bugs-return-471527-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Dec 22 02:26:43 2014
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From: "egall at gwmail dot gwu.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/61864] Feature Request, -Wcovered-switch-default to identify "dead" default branch
Date: Mon, 22 Dec 2014 02:26:00 -0000
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Eric Gallager <egall at gwmail dot gwu.edu> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |egall at gwmail dot gwu.edu
--- Comment #2 from Eric Gallager <egall at gwmail dot gwu.edu> ---
this(In reply to Chengnian Sun from comment #0)
> Currently, GCC supports -Wswitch and -Wswitch-enum.
It also supports "-Wswitch-default", which seems to be the exact opposite of
clang's "-Wcovered-switch-default". Personally I think gcc's "-Wswitch-default"
is the better one to listen to; having a default case is a good back-up even if
it will never actually be reached. Here is a link to a post that explains it
better than I could: http://programmers.stackexchange.com/a/242896/161051
^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug c++/64372] Spurious warning with throw in ternary operator returning const reference
2014-12-21 18:43 [Bug c++/64372] New: Spurious warning with throw in ternary operator returning const reference tavianator at gmail dot com
2014-12-22 0:49 ` [Bug c++/64372] " manu at gcc dot gnu.org
@ 2014-12-22 7:31 ` harald at gigawatt dot nl
2014-12-22 7:38 ` tavianator at gmail dot com
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: harald at gigawatt dot nl @ 2014-12-22 7:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64372
Harald van Dijk <harald at gigawatt dot nl> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |harald at gigawatt dot nl
--- Comment #2 from Harald van Dijk <harald at gigawatt dot nl> ---
(In reply to Manuel López-Ibáñez from comment #1)
> Probably even:
>
> const char&
> foz(const char* p)
> {
> return *p;
> }
>
> is undefined.
No, that is fine. *p is an lvalue already, so no temporary gets created.
The original code was supposed to get a warning because ptr ? *ptr : throw ptr
was not an lvalue: for a ? b : c to be an lvalue, both b and c needed to be
lvalues.
However, the C++ standard has since changed, and if one operand is a
throw-expression, and the other is an lvalue, the result is now an lvalue. CWG
issue 1560:
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1560
So in -std=c++11 mode, there should be no temporary, and no warning. (I haven't
checked if current versions of GCC already implement that, but I can find no
bug reports about it.)
>From gcc-bugs-return-471532-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Dec 22 07:32:50 2014
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From: "harald at gigawatt dot nl" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/64372] Spurious warning with throw in ternary operator returning const reference
Date: Mon, 22 Dec 2014 07:32:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd372
--- Comment #3 from Harald van Dijk <harald at gigawatt dot nl> ---
BTW, *(ptr ? ptr : throw ptr) would be fine, would not create any temporary, in
any of the language standards.
^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug c++/64372] Spurious warning with throw in ternary operator returning const reference
2014-12-21 18:43 [Bug c++/64372] New: Spurious warning with throw in ternary operator returning const reference tavianator at gmail dot com
2014-12-22 0:49 ` [Bug c++/64372] " manu at gcc dot gnu.org
2014-12-22 7:31 ` harald at gigawatt dot nl
@ 2014-12-22 7:38 ` tavianator at gmail dot com
2014-12-23 14:15 ` [Bug c++/64372] [DR1560] Gratuitous lvalue-to-rvalue conversion in conditional-expression with throw-expression operand harald at gigawatt dot nl
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: tavianator at gmail dot com @ 2014-12-22 7:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64372
--- Comment #4 from Tavian Barnes <tavianator at gmail dot com> ---
I meant to include -std=c++11 in the OP, it still happens with that flag set.
Good suggestion for the replacement though. The actual code was closer to i <
length ? a[i] : throw ... but I guess that can become (i < length ? a : throw
...)[i].
^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug c++/64372] [DR1560] Gratuitous lvalue-to-rvalue conversion in conditional-expression with throw-expression operand
2014-12-21 18:43 [Bug c++/64372] New: Spurious warning with throw in ternary operator returning const reference tavianator at gmail dot com
` (2 preceding siblings ...)
2014-12-22 7:38 ` tavianator at gmail dot com
@ 2014-12-23 14:15 ` harald at gigawatt dot nl
2021-07-23 0:06 ` pinskia at gcc dot gnu.org
2021-07-31 22:02 ` pinskia at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: harald at gigawatt dot nl @ 2014-12-23 14:15 UTC (permalink / raw)
To: gcc-bugs
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64372
--- Comment #7 from Harald van Dijk <harald at gigawatt dot nl> ---
(In reply to Manuel López-Ibáñez from comment #6)
Even that is probably too much right now. :) I do hope to be able to make some
bigger contributions in the future (in code too), and I really appreciate your
comment.
>From gcc-bugs-return-471634-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Dec 23 14:22:23 2014
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From: "alan at birtles dot org.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/64385] New: odd behaviour of std::is_move_constructible< std::ostringstream >
Date: Tue, 23 Dec 2014 14:22:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd385
Bug ID: 64385
Summary: odd behaviour of std::is_move_constructible<
std::ostringstream >
Product: gcc
Version: 4.9.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: alan at birtles dot org.uk
Created attachment 34320
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id4320&actioníit
file to reproduce the bug
When compiling the attached code without "A" defined the code outputs 0, 0
which is expected as std::ostringstream doesn't have a move constructor in gcc
4.9. However when "A" is defined the code outputs 1, 1 which is incorrect.
Compiled with "g++ test.cpp -std=c++11 -D A" on Ubuntu 14.10.
g++ --version:
g++ (Ubuntu 4.9.1-16ubuntu6) 4.9.1
^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug c++/64372] [DR1560] Gratuitous lvalue-to-rvalue conversion in conditional-expression with throw-expression operand
2014-12-21 18:43 [Bug c++/64372] New: Spurious warning with throw in ternary operator returning const reference tavianator at gmail dot com
` (3 preceding siblings ...)
2014-12-23 14:15 ` [Bug c++/64372] [DR1560] Gratuitous lvalue-to-rvalue conversion in conditional-expression with throw-expression operand harald at gigawatt dot nl
@ 2021-07-23 0:06 ` pinskia at gcc dot gnu.org
2021-07-31 22:02 ` pinskia at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-23 0:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64372
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |zhonghao at pku dot org.cn
--- Comment #17 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 86475 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 7+ messages in thread* [Bug c++/64372] [DR1560] Gratuitous lvalue-to-rvalue conversion in conditional-expression with throw-expression operand
2014-12-21 18:43 [Bug c++/64372] New: Spurious warning with throw in ternary operator returning const reference tavianator at gmail dot com
` (4 preceding siblings ...)
2021-07-23 0:06 ` pinskia at gcc dot gnu.org
@ 2021-07-31 22:02 ` pinskia at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-31 22:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64372
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |kaballo86 at hotmail dot com
--- Comment #18 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 61736 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 7+ messages in thread