[DX11] Compute Shader - shared memory problem

Graphics and GPU Programming Programming DX11

Started by Martin Perry March 07, 2012 01:09 PM

0 comments, last by MJP 12 years, 1 month ago

1,557

Author

March 07, 2012 01:09 PM

I have simple piece of code...

DecompressedShared is marked as groupshared, Decompressed is RWStructuredBuffer, lastDecompressedIndex is groupshared variable



uint index = 0;

for (uint j = lastDecompressedIndex; j < (lastDecompressedIndex + 2); j++)

{

  Decompressed[j] = DecompressedShared[index];

  index++;

}

Hovewer.. if I use code above, i got wrong result A | 0 | C | 0 ....
If I use this code instead:



    Decompressed[lastDecompressedIndex + 0] = DecompressedShared[0];

    Decompressed[lastDecompressedIndex + 1] = DecompressedShared[1];

I got correct result A | B | C | D ...

I dont understand it...

MJP

20,295

March 07, 2012 10:23 PM

You should check the assembly. I would bet that the compiler is going to do wacky things with that loop since it will have to re-load the value of lastDecompressedIndex for every loop iteration. I would try storing the value in a local variable so that it gets stored in a register, and see how that changes the resulting assembly code.

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