[Bug c++/109283] New: Destructor of co_yield conditional argument called twice

[Bug c++/109283] New: Destructor of co_yield conditional argument called twice

[ncm at cantrip dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109283

            Bug ID: 109283
           Summary: Destructor of co_yield conditional argument called
                    twice
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ncm at cantrip dot org
  Target Milestone: ---

Created attachment 54754
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54754&action=edit
Reproducer

Basically:

  co_yield a ? s : t;

segfaults,

  if (a) co_yield s; else co_yield t;

does not. The segfault traces to s/t's destructor being called 
twice. Full reproducer attached, relying on Casey Carter's 
generator implementation, pasted in.

This may be related to 101367.

Compiled with gcc-12.2, this program segfaults.
Compiled with gcc-trunk or gcc-coroutines on Godbolt, identified as:

  g++
(Compiler-Explorer-Build-gcc-13ec81eb4c3b484ad636000fa8f6d925e15fb983-binutils-2.38)
13.0.1 20230325 (experimental)

the compiler ICEs:

  <source>:513:1: internal compiler error: in flatten_await_stmt, at
cp/coroutines.cc:2899
  513 | }

[Bug c++/109283] Destructor of co_yield conditional argument called twice

[StevenSun2021 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109283

Steven Sun <StevenSun2021 at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |StevenSun2021 at hotmail dot com

--- Comment #1 from Steven Sun <StevenSun2021 at hotmail dot com> ---
It is indeed a bug. I currently only investigated into the gcc-12, it generates
something for

```
struct S{ /**/ };
bool w;

co_yield w ? S{"a"} : S{"b"};

```

pseudo-code for the generated gimple:

```
char __res[sizeof(S)];
char __a[sizeof(S)];
char __b[sizeof(S)];

new (__a) S("a");
new (__b) S("b");

if (w)
    memcpy(__res, __a, sizeof(S));
else
    memcpy(__res, __b, sizeof(S));

/*

...

*/

__b->~S();
__a->~S();
__c->~S();

```

So, clearly there is at least 3 bugs here:
i.   `__res` is never constructed.
ii.  only one of the `__a` and `__b` should be constructed, not both.
iii. the assignment is not corrected (it uses `gimple_assign` for value copy). 

If the ii is correctly implemented, iii will not happen.

Though, the code will work fine on all trivial types.

The correct code should be

```
char __res[sizeof(S)];

if (w)
    new (__res) S("a");
else
    new (__res) S("b");

/*

...

*/

__res->~S();

```

[Bug c++/109283] Destructor of co_yield conditional argument called twice

[ncm at cantrip dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109283

--- Comment #2 from ncm at cantrip dot org ---
Betting this one is fixed by deleting code.

[Bug c++/109283] Destructor of co_yield conditional argument called twice

[ncm at cantrip dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109283

--- Comment #3 from ncm at cantrip dot org ---
Appears fixed in 13.1

Still ICEs in trunk,
Compiler-Explorer-Build-gcc-70d038235cc91ef1ea4fce519e628cfb2d297bff-binutils-2.40)
14.0.0 20230508 (experimental):
<source>: In function 'std::generator<std::__cxx11::basic_string<char> >
source(int&, std::string)':
<source>:513:1: internal compiler error: in flatten_await_stmt, at
cp/coroutines.cc:2899
  513 | }

[Bug c++/109283] Destructor of co_yield conditional argument called twice

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109283

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-02-05
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |iains at gcc dot gnu.org

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to ncm from comment #3)
> Appears fixed in 13.1

It's likely that it's not fixed, it's just that the release branches do not
have as many consistency checks and assertions enabled as trunk does.

> 
> Still ICEs in trunk,
> Compiler-Explorer-Build-gcc-70d038235cc91ef1ea4fce519e628cfb2d297bff-
> binutils-2.40) 14.0.0 20230508 (experimental):
> <source>: In function 'std::generator<std::__cxx11::basic_string<char> >
> source(int&, std::string)':
> <source>:513:1: internal compiler error: in flatten_await_stmt, at
> cp/coroutines.cc:2899
>   513 | }

Confirmed.