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From: "StevenSun2021 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109283] Destructor of co_yield conditional argument called twice
Date: Wed, 29 Mar 2023 07:11:07 +0000	[thread overview]
Message-ID: <bug-109283-4-ZZ3iOFExWq@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109283-4@http.gcc.gnu.org/bugzilla/>

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();

```

  reply	other threads:[~2023-03-29  7:11 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-26  2:16 [Bug c++/109283] New: " ncm at cantrip dot org
2023-03-29  7:11 ` StevenSun2021 at hotmail dot com [this message]
2023-03-29 15:45 ` [Bug c++/109283] " ncm at cantrip dot org
2023-05-08 14:23 ` ncm at cantrip dot org
2024-02-05 14:23 ` redi at gcc dot gnu.org
2024-05-20 16:10 ` accelerator0099 at gmail dot com
2024-05-26  4:55 ` accelerator0099 at gmail dot com

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