llvm dev - Oct 2016 - Induction variable identification?

Hi,
How does LLVM identify induction variables of a loop?
Is the algorithm based on SSA graphs?

I have a complicated loop and I need to do some analysis around it.
Can anyone please point me to source of identification part?



-- 
*Disclaimer: Views, concerns, thoughts, questions, ideas expressed in this
mail are of my own and my employer has no take in it. *
Thank You.
Madhur D. Amilkanthwar
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If you have a canonicalized IV, you can use
Loop::getCanonicalInductionVariable() declared in
"include/llvm/Analysis/LoopInfo.h".

Otherwise you probably need to start from  function simplifyLoopIVs() in
"lib/Transforms/Utils/SimplifyIndVar.cpp". This method looks at all
phi
nodes in the header of the loop, but later on in the process, it skips some
of them. For example, when we reach SimplifyIndvar::simplifyUsers(), in the
beginning of this function we check if the IV data type isSCEVable() or
not. If not, we immediately return.

Hope that helps
Ehsan


On Sun, Oct 16, 2016 at 6:38 AM, Madhur Amilkanthwar via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
> How does LLVM identify induction variables of a loop?
> Is the algorithm based on SSA graphs?
>
> I have a complicated loop and I need to do some analysis around it.
> Can anyone please point me to source of identification part?
>
>
>
> --
> *Disclaimer: Views, concerns, thoughts, questions, ideas expressed in this
> mail are of my own and my employer has no take in it. *
> Thank You.
> Madhur D. Amilkanthwar
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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Hi Madhur,

If you're looking to solely _analyze_ induction variables, maybe you
should try leveraging LLVM's "Scalar Evolution" framework?  See
include/llvm/Analysis/ScalarEvolution.h for the docs or the
IndVarSimplify pass for examples.

Thanks,
-- Sanjoy

To be clear, I was suggesting to read the code in simplifyLoopIVs() in
"lib/Transforms/Utils/SimplifyIndVar.cpp" to see how it identifies
IVs. (as
opposed to calling the function to change the code).

On Sun, Oct 16, 2016 at 12:48 PM, Ehsan Amiri <ehsanamiri at gmail.com>
wrote:
> If you have a canonicalized IV, you can use Loop::
> getCanonicalInductionVariable() declared in "include/llvm/Analysis/
> LoopInfo.h".
>
> Otherwise you probably need to start from  function simplifyLoopIVs() in
> "lib/Transforms/Utils/SimplifyIndVar.cpp". This method looks at
all phi
> nodes in the header of the loop, but later on in the process, it skips some
> of them. For example, when we reach SimplifyIndvar::simplifyUsers(), in
> the beginning of this function we check if the IV data type isSCEVable() or
> not. If not, we immediately return.
>
> Hope that helps
> Ehsan
>
>
> On Sun, Oct 16, 2016 at 6:38 AM, Madhur Amilkanthwar via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi,
>> How does LLVM identify induction variables of a loop?
>> Is the algorithm based on SSA graphs?
>>
>> I have a complicated loop and I need to do some analysis around it.
>> Can anyone please point me to source of identification part?
>>
>>
>>
>> --
>> *Disclaimer: Views, concerns, thoughts, questions, ideas expressed in
>> this mail are of my own and my employer has no take in it. *
>> Thank You.
>> Madhur D. Amilkanthwar
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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