MIPS pseudo instructions

Pseudo-instructions

In MIPS, some operations can be performed with help of other instructions. The most common operations are unified in pseudo-instructions — they can be coded in assembly language, and assembler will expand them to real instructions. The exact expansion is compiler-defined, but the result should be similar to ours:

Data moves

Name Assembly syntax Expansion Operation in C move move $t, $s or $t, $s, $zero t = s clear clear $t or $t, $zero, $zero t = 0 load 16-bit immediate li $t, C ori $t, $zero, C_lo t = C load 32-bit immediate li $t, C

lui $t, C_hi
ori $t, $t, C_lo

t = C load label address la $t, A

lui $t, A_hi
ori $t, $t, A_lo

t = A

Branches

Name Assembly syntax Expansion branch unconditionally b C beq $zero, $zero, C branch unconditionally
and link bal C bgezal $zero, C branch if greater than bgt $s, $t, C

slt $at, $t, $s
bne $at, $zero, C

branch if less than blt $s, $t, C

slt $at, $s, $t
bne $at, $zero, C

branch if greater than
or equal bge $s, $t, C

slt $at, $s, $t
beq $at, $zero, C

branch if less than
or equal ble $s, $t, C

slt $at, $t, $s
beq $at, $zero, C

branch if greater than
unsigned bgtu $s, $t, C

sltu $at, $t, $s
bne $at, $zero, C

branch if zero beqz $s, C beq $s, $zero, C branch if equal to immediate beq $t, V, C

ori $at, $zero, V
beq $t, $at, C

branch if not equal to immediate bne $t, V, C

ori $at, $zero, V
bne $t, $at, C

Multiplication/Division

Name Assembly syntax Expansion Operation in C multiplicate
and return 32 bits mul $d, $s, $t

mult $s, $t
mflo $d

d = (s * t) & 0xFFFFFFFF quotient div $d, $s, $t

div $s, $t
mflo $d

d = s / t remainder rem $d, $s, $t

div $s, $t
mfhi $d

d = s % t

Jumps

Name Assembly syntax Expansion Operation in C jump register and link to ra jalr $s jalr $s, $ra ra = PC + 4; goto s;

Logical operations

Name Assembly syntax Expansion Operation in C not not $t, $s nor $t, $s, $zero t = ~s

No-operations

Name Assembly syntax Expansion Operation in C nop nop sll $zero, $zero, 0 {}

In fact, every MIPS instruction that has $zero as its destination and doesn't touch memory, access I/O system, and/or call a trap, can be treated as a nop; but using sll $zero, $zero, 0 is the most convenient because it's byte code is all-zeroes 0x00000000.

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Should we implement pseudo-instructions

Since 2014/2015, all instructions are printed as real MIPS instructions in MIPT-MIPS. Unexpanded pseudo-instructions are left only in testing traces source files (.s files).