llvm dev - Sep 2013 - [LLVMdev] How to get the exact integer from a Value

Hi,all
I have a Value* type named indexValue, and the type is i32.
I think "indexValue" must hold a number which type is int.
Now I want to use the exact number which pointed by indexValue , so I do
like this:

ConstantInt* CI = llvm::cast<llvm::ConstantInt>(indexValue); //This is
wrong, so is dyn_cast.
uint64_t index = indexValue->getZExtValue();
uint64_t size = index + 1;


I don't know if it is the right way.
So, could anybody tell the way to get the integer content from a Value*
which type is i32?

I'll be very very grateful if there is any answer.
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> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu]
> On Behalf Of weixuegong
> Subject: [LLVMdev] How to get the exact integer from a Value
> I have a Value* type named indexValue, and the type is i32.
> I think "indexValue" must hold a number which type is int.
Correct, but it might not be a constant.
> ConstantInt* CI = llvm::cast<llvm::ConstantInt>(indexValue); //This
is wrong, so is dyn_cast.
> uint64_t index = indexValue->getZExtValue();
> uint64_t size = index + 1;
Actually dyn_cast<> is what you want, used like this:

    ConstantInt* CI = dyn_cast<ConstantInt>(indexValue);
    int64_t index = (CI == NULL) ? -1 : CI->getZExtValue();

Note that you must use the result of the cast, not the original Value* variable.
Also, you must deal with the fact that the result of the cast might be NULL.

 - Chuck

Thank you, Chuck! It works.

And, please forgive my greed : ), another question:
I found that: In IR of llvm which generated by my testing code, there is 
a Inst said " getelementptr inbounds [5 x i32]* %idxarr, i32 0, i64
3".
The idxarr is my array name, and I think Inst means getting the ptr of 
the 4th (3+1) element of array "idxarr", am I right?
So the question is: how can I add this Inst in IR (In other words, is 
there an API method in IRBuilder or other class to generate 
"getelementptr"?). I searched for a while, but I found nothing.
I will appreciate if you could give me some suggestion on this.

Thank you.
>> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu]
>> On Behalf Of weixuegong
>> Subject: [LLVMdev] How to get the exact integer from a Value
>> I have a Value* type named indexValue, and the type is i32.
>> I think "indexValue" must hold a number which type is int.
> Correct, but it might not be a constant.
>
>> ConstantInt* CI = llvm::cast<llvm::ConstantInt>(indexValue);
//This is wrong, so is dyn_cast.
>> uint64_t index = indexValue->getZExtValue();
>> uint64_t size = index + 1;
> Actually dyn_cast<> is what you want, used like this:
>
>      ConstantInt* CI = dyn_cast<ConstantInt>(indexValue);
>      int64_t index = (CI == NULL) ? -1 : CI->getZExtValue();
>
> Note that you must use the result of the cast, not the original Value*
variable.  Also, you must deal with the fact that the result of the cast might
be NULL.
>
>   - Chuck
>
>