RegisterTest doesn't allow using sp

[Google Code Exporter]

Hi Markus!

Your OperatorsMarkusTest#RegisterTest doesn't allow me to read the 
StackPointer. Is that intentional? I don't see any issue with that...

Failure message:
  Error in RegisterTest (Subtest 3)
  You use registers you aren't allowed to use:   addiu $sp $t0 0     
  You might only use $v0, $v1 and $t0-$t9. 

Original issue reported on code.google.com by [e-mail] on 27 Jul 2012 at 2:20

[Google Code Exporter]

You don't need to use the stack pointer in this example. The expression 
requires only 10 registers to be evaluated, and cause it's an expression, you 
don't need a function body or anything similar that needs the stack pointer. So 
what do you want to do with the stack pointer?
In your example, addiu $sp $t0 0 looks like a move $sp $t0, so you're trying to 
write $sp. I guess $t0 is used for expression evaluation, so I don't think it's 
a good idea to overwrite the stack pointer with that. 

I think you need the stack pointer only in two cases: building/removing a 
function frame (not needed here) and maybe for expressions that are too large 
to evaluate in 12 registers, what isn't the case here. 

Maybe you have an error in your register management, so your code needs more 
registers than needed and trys to swap that on the stack? I had a similar 
mistake too. Make sure you always evaluate the bigger subtree first. 

Original comment by [e-mail] on 27 Jul 2012 at 4:38

[Google Code Exporter]

I certainly don't need to read the stack pointer for that expression, but it is 
allowed, so your test shouldn't fail.

> addiu $sp $t0 0 looks like a move $sp $t0
I suspect that the arguments are in the wrong order here. I definitely have 
some commands "addiu $t0 $so 0" in my code, but these only read the stack 
pointer.

I read the stack pointer because, for simplicity, I *always* use the stack to 
evaluate expressions, so I don't have to add a special handling for expressions 
needing more registers than available.

Original comment by [e-mail] on 27 Jul 2012 at 5:11

[Google Code Exporter]

I don't really know if it's allowed, the documentation says you should only use 
the registers $v0-$vv1, $t0-$t9 for expression evaluation. Perhaps we should 
ask Tobias if it's allowed. 

Another problem might be located in the LocalVariable class: loading a variable 
from the stack depends on the stack pointer, so if you change it, you'll load 
values from wrong points: 
asm.lw(target, Reg.sp, offset());

From this point, I suggest not allowing $sp because it results in a lot of hard 
to find errors. But if somebody is in the mood rewriting the LocalVariable 
class (or resetting the stack pointer before every variable load) we could 
maybe warn him instead of failing the test. 

Original comment by [e-mail] on 27 Jul 2012 at 6:39

[Google Code Exporter]

I don't "use" (write to) the stack pointer, I just read it.

That's also the reason why I don't get any problems with the LocalVariables.

Am 27.07.2012 um 20:39 schrieb "[e-mail]"
<[e-mail]>:

Original comment by [e-mail] on 27 Jul 2012 at 6:44

[Google Code Exporter]

Ok, in this case I suggest we allow $sp and write a warning in the console not 
to write it. I'll update my testfile within the next hour. 
I also posted the question in the forum, maybe we'll get a definite answer. 
https://forum.st.cs.uni-saarland.de/boards/viewthread?thread=1576

Original comment by [e-mail] on 27 Jul 2012 at 6:59

[Google Code Exporter]

OK, that sounds reasonable. Thank you!

Am 27.07.2012 um 21:00 schrieb "[e-mail]"
<[e-mail]>:

Original comment by [e-mail] on 27 Jul 2012 at 7:03

[Google Code Exporter]

Ok here's the updated version. Only fails if you're writing $sp (with 
additional message). Version is 1.2
As usual, please no code reformator :D

Original comment by [e-mail] on 27 Jul 2012 at 7:18

Attachments:

• OperatorsMarkusTest.java

[Google Code Exporter]

Thank you! I pushed your update.
I'll leave that open until we get a reply from Tobias.

Original comment by [e-mail] on 27 Jul 2012 at 7:24

• Changed state: Accepted

[Google Code Exporter]

Tobias replied here: 
https://forum.st.cs.uni-saarland.de/boards/viewthread?thread=1576
I'll close the issue now. Thank you for the update!

Original comment by [e-mail] on 27 Jul 2012 at 7:45

• Changed state: Fixed