1. A computer programmed as a high level shader language compiler having shader code optimizing transforms, comprising: a memory storing programming of the compiler; a processor for executing the programming; the programming of the compiler comprising: program code of a reorder transform operating to reorder instructions of the shader according to a heuristic measure prioritizing subsets of instructions that reduce active register load of the shader in an instruction sequence of the shader; program code of a phase pulling transform operating to organize the shader's instructions into phases of texture load instructions and arithmetic instructions that tend to minimize the number of such phases; program code of a register assigning transform operating to assign registers for instruction operands that tend to minimize register load of the shader.