MIPS "la" pseudo instruciton

assembly mips mars-simulator
darksky picture darksky · Nov 28, 2011 · Viewed 25.6k times · Source

In MIPS, the la instruction translates into lui and ori. However, MARS Simulator does not seem to do that at all. When I dump the following machine code:

.text
    la $a0, array
    la $a1, array_size
    lw $a1, 0($a1)

.data
    array: .word 0:10
    array_size: .word 10
    message: .asciiz "The sum of numbers in array is: "

I get:

00100000000001000010000000000000
00100000000001010010000000101000
10001100101001010000000000000000

Which is obviously. It is dumping la as one instruction. What does MARS do? How can I make it interpret la as lui and ori?

Thank you,

Answer

duskwuff -inactive- picture duskwuff -inactive- · Nov 28, 2011

What's happening here is that your assembler is compiling these las as addi $<dest>, $0, <value>. The two-instruction sequence is only required for values which can't be represented in a 16-bit immediate; the values you're using here look like 0x2000 and 0x2028, so they fit in a single instruction.

How can I make it interpret la as lui and ori?

Load bigger constants. :) Your assembler might also have an option to force the use of the full sequence even when it's unnecessary.

Related questions

Creating (and accessing) an array in MIPS

I'm trying to create an array in MIPS Assembly, and then add all the elements together. However, when I try to assemble the following, it says Error in read_array line 1 position 7: ".word" directive cannot appear in text segment Assemble: …

Read More
MIPS Address out of range (MARS)

I'm trying to write a simple code which save string and integer input into an array and then prints them (i will also later add another part which sorts them,but i have to get this to work first). .data …

Read More
Accessing one character in a string

I am using something like SPIMS or MARS with syscall functions. I am reading in a string (and it works because I can print it out) as follows: li $v0, 8 la $a0, string li $a1, 256 syscall However, I am having …

Read More