US Patent 7634637 Execution of parallel groups of threads with per-instruction serialization

In a processor, a SIMD group (a group of threads for which instructions are issued in parallel using single instruction, multiple data instruction issue techniques) is logically divided into two or more “SIMD subsets,” each containing one or more of the threads in the SIMD group. Each SIMD subset is associated with a different instance of a variable state parameter. The processor determines which of the instructions to be executed for the SIMD group rely on the state variable and serializes execution of such instructions so that the instruction is executed separately for each SIMD subset. Instructions that do not rely on the state variable are advantageously not serialized.