What's the difference between using ori and addi to initialize a value in MIPS?

Question

When I want to store a value in an address in MIPS, say the value 3 in $a0, I usually just use addi $a0, $0, 3. Sometimes I see people do this using ori $a0, $0, 3. Is one better than the other? What's the difference?

Answer 1

There are some subtle differences between the two:

ADDI :

• Sign -extends the immediate.
• Can result in integer overflow exceptions (can be avoided by using ADDIU instead).

ORI :

• Zero -extends the immediate.
• Not susceptible to integer overflow.