[Numpy-discussion] New iterator API (nditer): Overlap detection in NumPy

[Sebastian Berg]

Hi all,

Pauli just opened a nice pull request [1] to add overlap detection to
the new iterator, this means adding a new iterator flag:

`NPY_ITER_COPY_IF_OVERLAP`

If passed to the iterator (also exposed in python), the iterator will
copy the operands such that reading and writing should only occur for
identical operands. For now this is implemented by always copying the
output/writable operand (this could be improved though, so I would not
say its fixed API).

Since adding this flag is new API, please feel free to suggest other
names/approaches or even decline the change ;).


This is basically a first step, which should be easily followed by
adding overlap detection to ufuncs, removing traps such as the well (or
not so well known) `a += a.T`. Other parts of numpy may follow one by
one.

The work is based on his older awesome new memory overlap detection
implementation.

If there are no comments, I will probably merge it very soon, so we can
look at the follow up things.

- Sebastian


[1] https://github.com/numpy/numpy/pull/8026
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