SPIR-V states its an int, float, vector n (where n <= 4) or a matrix (2..4 cols of vector n).
It does not necessarily mean the hardware can do 4x4x64 floating point operations in a single subgroup operation, but at least the programming model supports framing it that way.
It does not necessarily mean the hardware can do 4x4x64 floating point operations in a single subgroup operation, but at least the programming model supports framing it that way.