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* [Bug c++/100405] New: missing return assignment
@ 2021-05-03 20:27 redi at gcc dot gnu.org
2021-05-03 20:28 ` [Bug c++/100405] " redi at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2021-05-03 20:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100405
Bug ID: 100405
Summary: missing return assignment
Product: gcc
Version: 10.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/100405] missing return assignment
2021-05-03 20:27 [Bug c++/100405] New: missing return assignment redi at gcc dot gnu.org
@ 2021-05-03 20:28 ` redi at gcc dot gnu.org
2021-05-03 20:40 ` [Bug c++/100405] Add implicit 'return *this;' in assignment operators redi at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2021-05-03 20:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100405
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oops, I hit enter in the Summary field and submitted this too soon. Please
ignore (for now).
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/100405] Add implicit 'return *this;' in assignment operators
2021-05-03 20:27 [Bug c++/100405] New: missing return assignment redi at gcc dot gnu.org
2021-05-03 20:28 ` [Bug c++/100405] " redi at gcc dot gnu.org
@ 2021-05-03 20:40 ` redi at gcc dot gnu.org
2021-05-03 22:22 ` redi at gcc dot gnu.org
2021-05-03 22:38 ` jakub at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2021-05-03 20:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100405
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|missing return assignment |Add implicit 'return
| |*this;' in assignment
| |operators
Resolution|INVALID |---
Severity|normal |enhancement
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=85523
Last reconfirmed| |2021-05-03
Ever confirmed|0 |1
Status|RESOLVED |NEW
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It would be nice if G++ would Do The Right Thing here:
struct T
{
T& operator=(const T& t)
{
i = t.i;
/* forgot to write return *this; */
}
int i = 0;
};
If the user forgets to write 'return *this;' in an assignment operator the
results can be quite unpleasant (after optimization).
Similar to the implicit 'return 0;' in main it would be nice to add an implicit
return *this to assignment operators. It could be done in cases where
-Wreturn-type warns (e.g. there isn't a throw or a call to a noreturn function
before the end of the function) and if the return type is decltype(*this).
G++ does give a -Wreturn-type warning for the example above (and since gcc 9 it
adds a fix-it hint, thanks to PR 85523) but for a template it doesn't warn
until it's instantiated:
template<typename>
struct T
{
T& operator=(const T& t)
{
i = t.i;
/* forgot to write return *this; */
}
int i = 0;
};
This compiles without a warning (which is PR 48586).
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/100405] Add implicit 'return *this;' in assignment operators
2021-05-03 20:27 [Bug c++/100405] New: missing return assignment redi at gcc dot gnu.org
2021-05-03 20:28 ` [Bug c++/100405] " redi at gcc dot gnu.org
2021-05-03 20:40 ` [Bug c++/100405] Add implicit 'return *this;' in assignment operators redi at gcc dot gnu.org
@ 2021-05-03 22:22 ` redi at gcc dot gnu.org
2021-05-03 22:38 ` jakub at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2021-05-03 22:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100405
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Another option would be to add an implicit __builtin_trap() there. Failing hard
is probably preferable to the kind of surprising behaviour you get from the
optimizers today.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/100405] Add implicit 'return *this;' in assignment operators
2021-05-03 20:27 [Bug c++/100405] New: missing return assignment redi at gcc dot gnu.org
` (2 preceding siblings ...)
2021-05-03 22:22 ` redi at gcc dot gnu.org
@ 2021-05-03 22:38 ` jakub at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-05-03 22:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100405
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
That is already supported with -fsanitize-undefined-trap-on-error
-fsanitize=unreachable or -fsanitize=unreachable.
It isn't always the best choice though, e.g. for functions with switches or ifs
where the compiler can't prove it doesn't fallthru into end of function but the
user is certain, having __builtin_trap or __ubsan_handle_builtin_unreachable is
certainly more expensive than __builtin_unreachable.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2021-05-03 20:27 [Bug c++/100405] New: missing return assignment redi at gcc dot gnu.org
2021-05-03 20:28 ` [Bug c++/100405] " redi at gcc dot gnu.org
2021-05-03 20:40 ` [Bug c++/100405] Add implicit 'return *this;' in assignment operators redi at gcc dot gnu.org
2021-05-03 22:22 ` redi at gcc dot gnu.org
2021-05-03 22:38 ` jakub at gcc dot gnu.org
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