1. A method for generating shader microcode for execution by a processing unit, the method comprising: receiving a shader program comprised of both assembly instructions configured to be executed by a specific target execution unit within the processing unit and a set of assembly instructions from a unified shader program assembly instruction set that is configured to be executed by each target execution unit within the processing unit, including a vertex execution unit and a fragment execution unit, determining, based on a tag in the shader program, the specific target execution unit within the processing unit that is supposed to execute the shader program, wherein the specific target execution unit comprises either the vertex execution unit or the fragment execution unit; and converting, by a single unified microcode assembler regardless of whether the shader program relates to vertex shading or fragment shading, the shader program into shader microcode for execution by the specific target execution unit within the processing unit.