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digitalmars.D.bugs - [Issue 10789] New: Struct destructor erroneously called

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           Summary: Struct destructor erroneously called
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: sludwig outerproduct.org


--- Comment #0 from Sönke Ludwig <sludwig outerproduct.org> 2013-08-09 22:54:25
PDT ---
The attached program simulates a simple reference counted struct. 'fun' is
supposed to return a newly initialized S with a count of 1. Instead it calls
the destructor dropping the count to zero and then returns a copy of the
initialized struct. Leaving out the 'if' statment and returning the fresh 'S'
directly does not exibit this behavior.

This issue is critical as it has a high probability to indroduce hard to
detect/track down bugs when automatic reference counting is used.

Tested on DMD 2.063.2/Win32 and /Win64 and DMD master/Win32.

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--- Comment #1 from Sönke Ludwig <sludwig outerproduct.org> 2013-08-09 22:55:04
PDT ---
Created an attachment (id=1241)
Reproduction case

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Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim maxim-fomin.ru


--- Comment #2 from Maxim Fomin <maxim maxim-fomin.ru> 2013-08-10 00:44:27 PDT
---
Reduced:

extern(C) int printf(const char*, ...);

struct S {
    static int count;

    this(int ignoreme)
    {
      int oldcount = count;
        printf("%X ctor %d=>%d\n", &this, oldcount, ++count);
    }

    ~this()
    {
      int oldcount = count;
        printf("%X dtor %d=>%d\n", &this, oldcount, --count);
    }

    this(this)
    {
      int oldcount = count;
        printf("%X postblit %d=>%d\n", &this, oldcount, ++count);
    }
}

S fun()
{
   S s1 = S(42), s2 = S(24);
    if (true) return s1;
   else return s2;
}

void main()
{
   S s = fun();
}

In case of if(true) compiler does not insert postblit call.

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--- Comment #3 from Sönke Ludwig <sludwig outerproduct.org> 2013-08-17 07:31:21
PDT ---
I digged a little in the DMD sources and found a commit by Kenji Hara that at
least affects this example and has a commented out code block that looks a
little suspicious :
https://github.com/D-Programming-Language/dmd/commit/b4bc25d72e601436f3999abc5c9c31e464385052#L4R1241

Changing "#if 0//DMDV2" back to "#if DMDV2" inserts a proper postblit call, but
then the returned t has its initialized field set to false. This does not
happen with the "#if 0" AFAICS. Unfortunately I know far to less about the
mechanics at work there to make an informed attempt to fix this.

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Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |regression


--- Comment #4 from Maxim Fomin <maxim maxim-fomin.ru> 2013-08-17 09:26:45 PDT
---
(In reply to comment #3)
 I digged a little in the DMD sources and found a commit by Kenji Hara that at
 least affects this example and has a commented out code block that looks a
 little suspicious :
 https://github.com/D-Programming-Language/dmd/commit/b4bc25d72e601436f3999abc5c9c31e464385052#L4R1241
 
 Changing "#if 0//DMDV2" back to "#if DMDV2" inserts a proper postblit call, but
 then the returned t has its initialized field set to false. This does not
 happen with the "#if 0" AFAICS. Unfortunately I know far to less about the
 mechanics at work there to make an informed attempt to fix this.
Sounds like a regression. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #5 from Kenji Hara <k.hara.pg gmail.com> 2013-09-03 21:45:29 PDT ---
https://github.com/D-Programming-Language/dmd/pull/2523

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--- Comment #6 from github-bugzilla puremagic.com 2013-09-03 22:53:21 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/4ca445bb2564997b80d5c00c6dfc1daeff1e30af
fix Issue 10789 - Struct destructor erroneously called

https://github.com/D-Programming-Language/dmd/commit/cfffc9b02fed9366babb6712cba7d6f26c18df6e
Merge pull request #2523 from 9rnsr/fix10789

[REG2.061] Issue 10789 - Struct destructor erroneously called

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


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Sönke Ludwig <sludwig outerproduct.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


--- Comment #7 from Sönke Ludwig <sludwig outerproduct.org> 2013-09-29 04:38:40
PDT ---
The original test case still fails on DMD HEAD:

---
0018FD74 this() 0
0018FD75 this(this) 1
0018FD74 ~this() 2
0018FD9C ~this() 1
core.exception.AssertError app(47): Assertion failure
---

This is due to the last destructor running on an uninitialized instance
(initialized == false).

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--- Comment #8 from Kenji Hara <k.hara.pg gmail.com> 2013-09-29 08:36:03 PDT ---
(In reply to comment #7)
 The original test case still fails on DMD HEAD:
 
 ---
 0018FD74 this() 0
 0018FD75 this(this) 1
 0018FD74 ~this() 2
 0018FD9C ~this() 1
 core.exception.AssertError app(47): Assertion failure
 ---
 
 This is due to the last destructor running on an uninitialized instance
 (initialized == false).
To me it looks like that the original test case contains a bug. In S.this(this), `initialized` field is incorrectly set to false. It will stop to decrement S.count at the destruction of the copied objects. Therefore the last assertion in main fails because S.count == 1. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Sönke Ludwig <sludwig outerproduct.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |FIXED


--- Comment #9 from Sönke Ludwig <sludwig outerproduct.org> 2013-09-29 09:20:09
PDT ---
Sorry, you are absolutely right. The "initialized = false" was supposed to go
to the destructor instead to test if the destructor is called twice on the same
instance. I'm still seeing a similar issue in my project, but I can't reproduce
it with the fixed this(this).

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