https://issues.dlang.org/show_bug.cgi?id=24436

Adam D. Ruppe <destructionator@gmail.com> changed:

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                 CC|                            |destructionator@gmail.com

--- Comment #1 from Adam D. Ruppe <destructionator@gmail.com> ---
I can reproduce, it seems random though; sometimes rebuilding with the same settings works and sometimes doesn't. I feel like I've seen this before too.

So definitely some kind of bug here.

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https://issues.dlang.org/show_bug.cgi?id=24436

FeepingCreature <default_357-line@yahoo.de> changed:

           What    |Removed                     |Added
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                 CC|                            |default_357-line@yahoo.de

--- Comment #2 from FeepingCreature <default_357-line@yahoo.de> ---
Doesn't seem to be happening on Linux, even over a hundred builds and runs.

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https://issues.dlang.org/show_bug.cgi?id=24436

--- Comment #3 from Adam D. Ruppe <destructionator@gmail.com> ---
I had it happen on linux once...

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https://issues.dlang.org/show_bug.cgi?id=24436

--- Comment #4 from FeepingCreature <default_357-line@yahoo.de> ---
Huh. With the same build once, or with rebuild once? And how long until it happened? I had the code running in a loop and didn't see it, though I changed the writefln for an assert so maybe that changed it enough that it didn't happen. (Would be weird though.)

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https://issues.dlang.org/show_bug.cgi?id=24436

Tim <tim.dlang@t-online.de> changed:

           What    |Removed                     |Added
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                 CC|                            |tim.dlang@t-online.de

--- Comment #5 from Tim <tim.dlang@t-online.de> ---
I can reproduce the problem with the Arch Linux package for dmd v2.108.0. The
output is a bit different from the bug report:
[100, 101],[2, 3]
[100, 101],[102, 103]

This happens only with the Arch Linux package and not with the tar archive from dlang.org.

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https://issues.dlang.org/show_bug.cgi?id=24436

--- Comment #6 from Tim <tim.dlang@t-online.de> ---
Correction:

It does not happen with DMD 2.108, but DMD 2.107. I previously made a mistake while updating.

The problem happens with DMD 2.107 under Arch Linux with both the package and the tar archive from dlang.org.

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https://issues.dlang.org/show_bug.cgi?id=24436

--- Comment #7 from Tim <tim.dlang@t-online.de> ---
The first bad commit seems to be https://github.com/dlang/dmd/commit/055accfbe6afe5f72c77617d54f737e71e29f5a3

The problem does not happen any more since this commit: https://github.com/dlang/dmd/commit/1778ab8876bbee178b098be4baa1e2ad059a1769

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https://issues.dlang.org/show_bug.cgi?id=24436

Tim <tim.dlang@t-online.de> changed:

           What    |Removed                     |Added
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           Severity|normal                      |regression

--- Comment #8 from Tim <tim.dlang@t-online.de> ---
Unfortunately the second commit has not fixed the problem. It can still be seen with 3x3 arrays.

import std.stdio, core.memory;

void main()
{
        int[][] array1, array2;
        array1 = new int[][](3,3);
        foreach (row; 0 .. 3)
        {
                foreach (col; 0 .. 3)
                {
                        array1[row][col] = col+row*3;
                }
        }
        GC.collect();
        array2 = new int[][](3,3);
        foreach (row; 0 .. 3)
        {
                foreach (col; 0 .. 3)
                {
                        array2[row][col] = 100+col+row*3;
                }
        }
        writefln("%(%s,%)", array1);
        writefln("%(%s,%)", array2);
}

DMD 2.106.0:
[0, 1, 2],[3, 4, 5],[6, 7, 8]
[100, 101, 102],[103, 104, 105],[106, 107, 108]

DMD 2.107.1:
[100, 101, 102],[103, 104, 105],[6, 7, 8]
[100, 101, 102],[103, 104, 105],[106, 107, 108]

DMD 2.108.0:
[0, 1, 2],[100, 101, 102],[6, 7, 8]
[100, 101, 102],[103, 104, 105],[106, 107, 108]

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https://issues.dlang.org/show_bug.cgi?id=24436

--- Comment #9 from Tim <tim.dlang@t-online.de> ---
Here is a more direct test:

```
import core.memory;

void main()
{
        int[][] array1 = new int[][](2,2);
        assert(!(GC.getAttr(array1.ptr) & GC.BlkAttr.NO_SCAN)); // fails now
        assert(GC.getAttr(array1[0].ptr) & GC.BlkAttr.NO_SCAN); // passes

        int*[][] array2 = new int*[][](2,2);
        assert(!(GC.getAttr(array2.ptr) & GC.BlkAttr.NO_SCAN)); // passes
        assert(!(GC.getAttr(array2[0].ptr) & GC.BlkAttr.NO_SCAN)); // passes
}
```

The attributes are wrong for the outer array of array1. As a result the GC does not scan it and reuses the memory for the inner arrays.

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https://issues.dlang.org/show_bug.cgi?id=24436

--- Comment #10 from FeepingCreature <default_357-line@yahoo.de> ---
Great repro! Yeah that makes it pretty obvious what's happening. I'm on it.

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