[LLVMdev] Printing Function Arguments

[ivtm]

Hi Nick,

Perhaps I am confused. What is the best way to extract information from
instructions ?

Is it via the, say:

for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
    ....

I am not sure what happens next, e.g. to the variable 'i', you should know 
what part of the instruction this is and cast it to the necessary type.

For example, I am parsing the 'inttoptr' instruction.

In that case the loop iterates only once, but then, I want to extract the
values
from which I am casting, _and_ the value to which I am casting. Somehow I
need to
extract the contents of the 'i'.

For that, there are functions like getSrcTy() and getDstTy() 
I found them again by browsing the header files (which is not right :)...
say for the inttoptr instruction.

Btw, also the cout << I->getName() returns an empty string for some reason.
I tried I->getName().c_str(), but still the same.

Some simple example, say of parsing 'load' or 'add' would be great....

Also, I assume when you say registers are immutable, you mean within the
same instruction instance.
I can have a loop that updates the same register.

thanks for your help....I just need to parse successfully few instructions
and I will be done, but right now I am struggling.


Nick Lewycky wrote:
> 
> ivtm wrote:
>> Hey Oscar,
>> 
>> I want to extract information from the instruction.
>> 
>> Think writing a simple interpreter.
>> 
>> I already have the CallInst instance (described above in the message).
>> 
>> Via ci->getOperand(1) say I can get the 'i32 8' parameter and I can get
>> the
>> 'i32' and '8' separately as Nick described.
>> 
>> But I need to extract the %0 from the CallInst instance somehow. I am not
>> sure what the exact method to call is.
>> 
>> I need that btw, for every instruction that writes, e.g. loads, adds,
>> muls,
>> etc...There has got to be a generic method for that. 
> 
> This is a common misunderstanding. When you look at something like:
> 
>    %a = add i32 %x, %y
> 
> it's common to think "Well, I've got the Instruction* which is on the 
> right hand side, how do I get the %a on the left hand side"? The answer 
> is that the whole thing is actually:
> 
>    %I->getName() = I->getOpcode() I->op_begin()..I->op_end()
> 
> There is only the Instruction *I. It _is_ the value that it produces. 
> There is no register it's being stored into, that Instruction* is itself 
> the definition of the register!
> 
> Note that registers are immutable (being a static single assignment 
> form) and that we have an infinite register set.
> 
> Nick
> 
>> I am looking at the existing LLVM passes to figure out how they extract
>> stuff, but since many are only computing the small relevant info that
>> they
>> need, they do not always need to extract all the components of an
>> instruction. (I've looked at the interpreter too, but it is doing other
>> stuff).
>> 
>> Anyway..concretely, I need to extract the return register for an
>> instruction.
>> 
>> 
>> 
>> Óscar Fuentes wrote:
>>> ivtm <martinaide1 at yahoo.com> writes:
>>>
>>>> Another question, I need to get the "%0" below in the:
>>>>
>>>> %0 = tail call i32 (...)* @__FFF (i32 8) nounwind; <i32> [#uses=1]
>>>>
>>>> that is, the return register. 
>>> What information do you want, exactly?
>>>
>>> In your example, %0 is the CallInst. So if you have
>>>
>>> CallInst *ci = CallInst::Create(...
>>>
>>> then use `ci' whenever you want to use %0.
>>>
>>>> I am wondering in general, where should I look in the llvm codebase for
>>>> parsing instructions ?
>>>>
>>>> I am looking at existing passes and also the header files like
>>>> Function.h,
>>>> etc to see what methods they have, but it takes a while to figure out
>>>> the
>>>> basic methods...
>>> This is a bit better than looking at header files:
>>>
>>> http://llvm.org/doxygen/classes.html
>>>
>>> -- 
>>> Óscar
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>> 
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> 

-- 
View this message in context: http://www.nabble.com/Printing-Function-Arguments-tp25638981p25640679.html
Sent from the LLVM - Dev mailing list archive at Nabble.com.