Two Basic Instructions

Machine instructions have fixed-sized fields. Immediate operands are always 16 bits. However, two machine instructions can be used to load a 32-bit register with the top half and bottom half of a 32-bit integer:

li $v1,0x12345678

==

lui $v1,0x1234 ori $v1,$v1,0x5678

Here, li is translated into two basic instructions. The first loads the top half of $v1. The second uses the ori operation to load the bottom half. This is done for any integer (positive or negative) that requires more bits than an immediate operand can hold.

So, the extended assembly language programmer has a very useful instruction:

li   d,value        #  load register $d with the 
                    #  positive or negative integer
                    #  "value".  Value may be a 
                    #  any integer up to 32 bits. 
                    #  (pseudoinstruction)

The extended assembler automatically translates this pseudoinstruction into the most efficient sequence of actual instructions.