[LLVMdev] Question about use-def chain

[Bill Wendling]

Hi 신건철,

On Mar 12, 2008, at 12:22 AM, 신건철 wrote:
> Programmers’ manual says we can iterate over a use-def chain by  
> op_iterator.
>
> It works fine except for load and store instruction of stack  
> variables.
>
>
>
> For example, a simple bitcode is like the below.
>
> i = alloca i32
>
> store i32 0, i32* %i, align 4
>
> %tmp1 = load i32* %i, align 4
>
>
>
> If I apply a use-def chain to load instruction, I get alloca  
> instruction.
>
> I think store instruction is a correct use-def chain.
>
> Am I right?
>
> Is there any other method to iterate over a use-def chain in this  
> case?
>
The op_iterator will tell you what definitions the instruction uses.  
So in this case, the "alloca" instruction is the correct one because  
the store instruction isn't defining %i. If you were to iterate over  
the uses of the alloca instruction, then you would get the "store"  
and "load" instructions.

If you're trying to determine that %i is the same value for both the  
"store" and "load" instructions, then you'll probably want to compare  
the op_iterator values for both the "store" and "load" and see if  
they match. For example, %i in this case matches, because %i isn't  
redefined between the store and the load.

-bw