[LLVMdev] Trace Use-Def chain

[tarun agrawal]

Thanks John,

I know how to iterate through def-use chains and I also have realized the
need for an algorithm to do the work. But the algorithm I am able to figure
out is not linear in time. It wold be a great help  if someone suggest me a
way to get all basic-block along all path between two instruction.

On Wed, May 4, 2011 at 7:00 AM, John Criswell <criswell at illinois.edu> wrote:

>  Dear Tarun,
>
> It just occurred to me that this may or may not be what you are asking
> about.  This only finds basic blocks along the def-use chain of an
> instruction; it does not find all basic blocks along all paths between two
> instructions.  I don't know of an algorithm off-hand for the latter, but if
> you understand how to iterate over def-use chains and the control-flow
> graph, then writing up an algorithm for the latter should be pretty easy.
>
> -- John T.
>
>
>
> On 5/3/11 8:24 PM, John Criswell wrote:
>
> 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>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
>>
>
>
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