li $v0,12 == ori $v0,zero,12

Several Translations

The load immediate pseudoinstruction is useful for loading a register with an integer value. Here is another example:

li  $t2,-153

This puts the two's complement representation of -156₁₀ into register $t2. However, this can not be done with ori because the immediate field of that instruction must be a 16-bit unsigned integer (which is zero-extended to 32 bits upon execution). Because the immediate value of the li is negative, a different translation is used:

 
li $v2,-153   ==   addiu $v2,$0,-153

(Remember that addiu performs two's complement addition with its operands. The u means that overflow does not cause a trap). The extended assembler translates li into different basic instructions depending on the sign of the immediate value.