[LLVMdev] Trace Use-Def chain

[John Criswell]

On 5/3/11 4:08 PM, tarun agrawal wrote:
> HI
>
> I know it is a very simple question not worth asking here but I am 
> really struggling pls help me out..

This is a question worth asking; it's just that not everyone can answer 
all the time.
:)

If all you want to do is to follow the SSA def-use chain within a single 
function, then this is very easy.  All you have to do is use the 
use_iterator of the Instruction object to iterate through its def-use 
chain.  For all uses that are instructions, use the getParent() method 
to find the basic block containing the instruction.  That's it.

This approach won't work in two cases:

1) If you want to trace def/use through memory.  Memory is not in SSA 
form, and so you have to use extra analysis to track from which store 
the result of a load originates.

2) If you want to track def/use inter-procedurally through function 
arguments and return values.  If you don't care about tracking through 
memory, this is a fairly easy inter-procedural analysis to do, and we 
have some code internally at University of Illinois that does it.  If 
you need it, I can talk to Vikram and see if we can give you a copy.

For more information on how to iterate through def-use chains, see the 
LLVM Programmer's Manual:
http://llvm.org/docs/ProgrammersManual.html#iterate_chains

-- John T.

>
> On Tue, May 3, 2011 at 10:10 PM, tarun agrawal <tarun at cse.iitb.ac.in 
> <mailto:tarun at cse.iitb.ac.in>> wrote:
>
>     Hi,
>
>     I need to get all the basic blocks that are there, in the path
>     from definition of an instruction to use of that instruction.
>
>
>     Regards
>     Tarun
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110503/ffb68e21/attachment.html>