[LLVMdev] Check the location of the definition of a Value object

[Zheng Wang]

Cheers John!


On 8 April 2010 17:25, John Criswell <criswell at uiuc.edu> wrote:
> Zheng Wang wrote:
>>
>> Hello,
>>
>> How to check whether a value object is within a particular basic block or
>> not.
>>
>
> There is a much simpler way to do this.  Assuming that Value * pb holds the
> pointer to the value of %2, you do the following:
>
> 1) Check to see if %2 is an instruction (use dyn_cast<Instruction>(pb) and
> see if the result is NULL).  If it's not an instruction, then it's
> definitely not defined in the entry block.
>
> 2) Use the result of dyn_cast<Instruction>(pb) to get the basic block in
> which the instruction is defined.
>
> So, you do
>
> // Entry is a Basic Block pointer pointing to the function's entry block
> if (Instruction * PBI = dyn_cast<Instruction>(pb)) {
>   if (PBI->getParent() == Entry)
>      // pb is an instruction defined in the entry basic block.
>
>
> -- John T.
>
>> I have the following LLVM bytecode:
>>
>> ------------------------
>> entry:
>>  ...
>>  %2 = call i32 (...)* @atoi(i8*%1) nounwind
>>  ...
>>
>> --
>> bb1:
>>  ..
>>  %5 = icmp sgt i32 %2, %i.0
>>  ...
>> -----------------
>>
>> Here I got the corresponding pointer of the Value object of *%2*. How
>> can I check whether it is defined in *entry* or not?
>>
>> I tried:
>> ---------------------
>> //Value* pb corresponding to %2
>> for (BasicBlock::iterator I=entry->begin(), e=entry.end(); I != e; I++)
>> {
>>       if (I == pb)
>>          return true;
>> }
>> return false;
>> ----------------------
>>
>> However, I got  errors when compiled the code. Could anyone give some
>> simple examples about this issue?
>>
>> Thanks.
>>
>> Cheers,
>> Zheng
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>>
>
>



-- 
Best regards,

WANG Zheng