llvm dev - Jul 2020 - Regarding the project "Create LoopNestPass"

Hi,

I'm a college student who is quite new to the community and is interested
in contributing to the LLVM project. Although I haven't applied to GSoC, I
notice that the project "Create LoopNestPass" seems to be unassigned.
So I'm curious whether anyone is currently working on it, and if not, is it
possible for me to work on it as a side-project?

I've been programming in C++ for quite a while, and I've walked through
the
`LoopPass`, `LoopNest`, and some other LLVM classes that I think would
probably be related to this project. I've also watched some of the videos
in the llvm-dev conference regarding loops, so I now have a rough idea on
how to implement the LoopNestPass.

I'm looking forward to working on this project.

Thank you very much.

Sincerely,
Ta-Wei Tu
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Hi Wayne,

As far as I know, no one is working on this project. Your contribution is
always appreciated.

This project aims to create LoopNestPass in the new pass manager (NPM).
In https://www.youtube.com/watch?v=3pRhvQi7Z10
<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.youtube.com_watch-3Fv-3D3pRhvQi7Z10&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=p0DGcdtx8-l1bvwJTLSk1zBTXpb78Y1slqHKTsTpRTE&m=PzTQj0kzu8kuCmHOMYatYGxUnZCBLnJ5ynt0qqlYoSE&s=nDqZ-LcpFAgM1uK4RSlRYDlhQE60FUZmOPjgdW5aTuo&e=>
,
you can try to follow along to create a LLVM loop pass in NPM.

There exist different kinds of passes in the NPM, e.g. ModulePass,
FunctionPass, LoopPass.
One or more loop passes can be added in a LoopPassManager, which then can
be added in FunctionPassManager through createFunctionToLoopPassAdaptor.
Examples can be found in llvm/lib/Passes/PassBuilder.cpp.
There exist passes that best operate as a loop nest, e.g. LoopInterchange.
For those passes, currently can be written as either FunctionPass or
LoopPass.
However, choosing one or the other needs to sacrifice the ability of the
other.
The idea of a LoopNestPass is to combine the benefits of FunctionPass and
LoopPass needed for a loop nest.

On top of LoopNest I would suggest to also get familiar with different
PassAdaptor classes (e.g. FunctionToLoopPassAdaptor).
- llvm/include/llvm/Transforms/Scalar/LoopPassManager.h

I am happy to provide feedback once you have a plan of how to proceed, or
review your patches on Phabricator.

Regards,
Whitney Tsang

On Wed, Jul 15, 2020 at 5:49 AM Wayne Tu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> I'm a college student who is quite new to the community and is
interested
> in contributing to the LLVM project. Although I haven't applied to
GSoC, I
> notice that the project "Create LoopNestPass" seems to be
unassigned.
> So I'm curious whether anyone is currently working on it, and if not,
is
> it possible for me to work on it as a side-project?
>
> I've been programming in C++ for quite a while, and I've walked
through
> the `LoopPass`, `LoopNest`, and some other LLVM classes that I think would
> probably be related to this project. I've also watched some of the
videos
> in the llvm-dev conference regarding loops, so I now have a rough idea on
> how to implement the LoopNestPass.
>
> I'm looking forward to working on this project.
>
> Thank you very much.
>
> Sincerely,
> Ta-Wei Tu
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi,

Thanks for your help! I've checked the sources that you mentioned.
Currently, I think that I would need to implement a
FunctionToLoopNestPassAdaptor which is essentially the same as the
FunctionToLoopPassAdaptor but operates only on LI.getTopLevelLoops().

We might also need a LNPMUpdater (LoopNestPassManagerUpdater) which
disallows adding inner-loops back into the pipeline, and
LoopNestPassManager will simply be PassManager<Loop, LoopAnalysisManager,
LoopStandardAnalysisResult &, LNPMUpdater &>.

One question I have is whether the IRUnit LoopNestPass operates on should
be Loop or LoopNest, since I'm not quite sure about the usage of LoopNest
and why it should be constructed with a ScalarEvolution.

Also, it is stated that "we want to create a LoopNestPass, where
transformations intended for loop nest can inherit from it" in the original
GSoC project description, but I believe that inheriting from a Pass
subclass is no longer required in the New Pass Manager. So should we also
implement a LoopNestPass subclass that allows implementing loop-nest-passes
for the Legacy Pass Manager?

Finally, I have some questions that might not be very relevant to the
project. But currently, how does the LegacyPassManager and the
NewPassManager interact? Also, is it possible to add passes designed for
LegacyPassManager into the NewPassManager and vice versa?

What do you think about the plan? I'm quite likely to miss something
important, so please kindly correct me if I'm in the wrong direction.

Thank you very much!
Sincerely, Ta-Wei Tu

Whitney Tsang <whitney.uwaterloo at gmail.com> 於 2020年7月15日 週三 下午6:14寫道：
> Hi Wayne,
>
> As far as I know, no one is working on this project. Your contribution is
> always appreciated.
>
> This project aims to create LoopNestPass in the new pass manager (NPM).
> In https://www.youtube.com/watch?v=3pRhvQi7Z10
>
<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.youtube.com_watch-3Fv-3D3pRhvQi7Z10&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=p0DGcdtx8-l1bvwJTLSk1zBTXpb78Y1slqHKTsTpRTE&m=PzTQj0kzu8kuCmHOMYatYGxUnZCBLnJ5ynt0qqlYoSE&s=nDqZ-LcpFAgM1uK4RSlRYDlhQE60FUZmOPjgdW5aTuo&e=>
,
> you can try to follow along to create a LLVM loop pass in NPM.
>
> There exist different kinds of passes in the NPM, e.g. ModulePass,
> FunctionPass, LoopPass.
> One or more loop passes can be added in a LoopPassManager, which then can
> be added in FunctionPassManager through createFunctionToLoopPassAdaptor.
> Examples can be found in llvm/lib/Passes/PassBuilder.cpp.
> There exist passes that best operate as a loop nest, e.g. LoopInterchange.
> For those passes, currently can be written as either FunctionPass or
> LoopPass.
> However, choosing one or the other needs to sacrifice the ability of the
> other.
> The idea of a LoopNestPass is to combine the benefits of FunctionPass and
> LoopPass needed for a loop nest.
>
> On top of LoopNest I would suggest to also get familiar with different
> PassAdaptor classes (e.g. FunctionToLoopPassAdaptor).
> - llvm/include/llvm/Transforms/Scalar/LoopPassManager.h
>
> I am happy to provide feedback once you have a plan of how to proceed, or
> review your patches on Phabricator.
>
> Regards,
> Whitney Tsang
>
> On Wed, Jul 15, 2020 at 5:49 AM Wayne Tu via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi,
>>
>> I'm a college student who is quite new to the community and is
interested
>> in contributing to the LLVM project. Although I haven't applied to
GSoC, I
>> notice that the project "Create LoopNestPass" seems to be
unassigned.
>> So I'm curious whether anyone is currently working on it, and if
not, is
>> it possible for me to work on it as a side-project?
>>
>> I've been programming in C++ for quite a while, and I've walked
through
>> the `LoopPass`, `LoopNest`, and some other LLVM classes that I think
would
>> probably be related to this project. I've also watched some of the
videos
>> in the llvm-dev conference regarding loops, so I now have a rough idea
on
>> how to implement the LoopNestPass.
>>
>> I'm looking forward to working on this project.
>>
>> Thank you very much.
>>
>> Sincerely,
>> Ta-Wei Tu
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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