[Bug 108875] Invalid subgroupSize for Intel GPU

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108875

--- Comment #2 from Alexander <frustumo at gmail.com> ---
I tried to run a simple compute shader to test subgroup instructions:

layout(local_size_x = subgroupSize) in;
layout(std430, binding = 0) writeonly buffer output_buffer { uint output[]; };
void main() {
  uint id = gl_GlobalInvocationID.x;
  output[id] = subgroupAdd(id);
}

The output on Intel is:
120  120  120  120  120  120  120  120  120  120  120  120  120  120  120  120
376  376  376  376  376  376  376  376  376  376  376  376  376  376  376  376
632  632  632  632  632  632  632  632  632  632  632  632  632  632  632  632
888  888  888  888  888  888  888  888  888  888  888  888  888  888  888  888

The real subgroup size is 16 on Intel (32 on NVidia and 64 on AMD hardware).

PS: It's interesting that subgroup size under Direct3D12 (DXIL shader) equals
to 8.

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