[Issue 24498] New: Multidimensional array not scanned by GC

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24498

          Issue ID: 24498
           Summary: Multidimensional array not scanned by GC
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: regression
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: tim.dlang at t-online.de

This is similar to issue 24436:

```
import std.stdio, core.memory;

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

The array has three dimensions, but only two are initialized. The middle arrays
need to be scanned by the GC, but they are marked as NO_SCAN. The problem
exists since
https://github.com/dlang/dmd/commit/055accfbe6afe5f72c77617d54f737e71e29f5a3

A similar problem has already been solved in
https://github.com/dlang/dmd/pull/16373

The initialization is lowered to _d_newarraymTX!(int[][][], int, int[][]).
Maybe this should be _d_newarraymTX!(int[][][], int[], int[][]) instead,
because the element type of the array should be int[] and not int.

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