[LLVMdev] Printing Function Arguments
martinaide1 at yahoo.com
Sun Sep 27 22:05:33 PDT 2009
Perhaps I am confused. What is the best way to extract information from
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
from which I am casting, _and_ the value to which I am casting. Somehow I
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
>> '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,
>> 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.
>> 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
>> 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
>> Anyway..concretely, I need to extract the return register for an
>> 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
>>>> etc to see what methods they have, but it takes a while to figure out
>>>> basic methods...
>>> This is a bit better than looking at header files:
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
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