[GEN] Implement GPU to GEN lowering

[FMarno]

Implements the lowering of the GPU dialect to the GEN dialect where possible.
Currently there are only 6 GEN operations, so the lowering is a bit limited.

Signed-off-by: Finlay Marno [email protected]

[FMarno]

@etiotto @whitneywhtsang In GPUShuffleToGENLowering, we were a bit unsure what to do with the width argument. GPU to SPIRV lowering checks that the width is constant and equal to the subgroup size, but I don't know if we can check the target information here. Do you have any ideas?

[victor-eds]

Just some minors

[whitneywhtsang]

@etiotto @whitneywhtsang In GPUShuffleToGENLowering, we were a bit unsure what to do with the width argument. GPU to SPIRV lowering checks that the width is constant and equal to the subgroup size, but I don't know if we can check the target information here. Do you have any ideas?

Target information is not currently available in GEN, we can check if it is one of the expected subgroup sizes (16, 32) for now.

[victor-eds]

Target information is not currently available in GEN, we can check if it is one of the expected subgroup sizes (16, 32) for now.

I'd say we keep this as is till we include a way to encode that in the dialect, i.e., an attribute.

[FMarno]

I'm just going to merge this for now, hopefully #13640 will gain traction and a proper solution for the subgroup shuffles can be found.