Picongpu: CUSTL shared memory allocation is wrong

[psychocoderHPC]

I am on the way to remove the last usage of __shared__ in PMacc.
I found that CUSTL is using the wrong index order to allocate N-dimensional shared memory.
CUSTL is using int mem[x][y][z]; but it must be int mem[z][y][x]; link to the code

Maybe it breaks nothing because later on the array is handled as 1-dimensional array and the plain data size is in both cases equal.

Currently it is not clear if this can have any side effects, never the less I marked this as BUG and that this effects the latest release.

[ax3l]

Well spotted, here is one usage in the phasespace plugin that I am aware of.

[Heikman]

In my opinion this is not a bug because the order of dimensions at instantiation is not relevant for the access pattern. Plus, the amount of allocated memory is the same.

[Heikman]

If the current case doesn't look well to you, I'd propose to make it more explicit: int mem[x*y*z];

[psychocoderHPC]

Yes I am currently flat out this shared memory and the same in PMacc::memory. We always touch the memory with own memory calculations, therefore we should use a flat memory storage.

[psychocoderHPC]

fixed with #1929