The TwoArrayRadixSort path causes memory corruption (?) when it is used with records that have array fields

[e-kayrakli]

... though this is probably a compiler bug that is exposed by TwoArrayRadixSort

use Sort;

record r {
  var keyField: real;
  var dummyField: [1..3] real;
}

record myComparator { }
proc myComparator.key(const ref obj: r){
  return obj.keyField;
}

config const n = 10;
var Arr: [1..n] r;

sort(Arr, comparator=new myComparator());
writeln(Arr[1]);

Here r is a record with a keyField and a dummyField that's not used. keyField is used while sorting the array Arr.

Any option avoiding the TwoArrayRadixSort path works. Namely, stable=true works, using 49999 element array works, 50000 doesn't as that's the TwoArrayRadixSort threshold.

I get

$CHPL_HOME/modules/internal/ChapelArray.chpl:1531: error: attempt to dereference nil

This is array deallocation code.

In the real case, I get similar errors, but the issue is harder to debug as it generates a core dump. My theory is that this is about deinitializing dummyField for the second array we use or some temporary. But I haven't looked any deeper into the sort code to understand.

The potential workaround is to use a tuple instead of an array for dummyField, assuming that it is relatively small.

[e-kayrakli]

Tagging @mppf because of his Sort expertise. The issue is most likely a compiler issue, but understanding the algorithm would be helpful in understanding the bug.