1. A method for instruction processing executing on a computer, comprising: identifying a classification of a functional unit which can execute a basic instruction; determining whether said basic instruction can be assigned to a logical instruction slot; determining whether said basic instruction is arranged in an allowable order; and assigning, to a physical instruction slot, said basic instruction determined to be assignable to said logical instruction slot by increasing a logical instruction slot pointer based on a relation between said basic instruction determined to be assignable and another basic instruction assigned to a corresponding logical instruction slot; wherein the computer is a variable length Very Long Instruction Word processor with a predefined allowable arrangement of basic instructions, the computer having a plurality of physical instruction slots and a plurality of functional units corresponding one-to-many or many-to-many, and the logical instruction slot is an imaginary instruction slot which corresponds to the functional unit.