[llvm-dev] GSoC Opportunity

Wed Mar 18 05:59:06 PDT 2020

Hi Raphael,

Thanks for the clarification. I note that in this case, I also think that
Benson should preferably find a different project as that would probably be
better for everybody.

Best,
Stefanos Baziotis

On Wed, Mar 18, 2020, 12:24 Raphael “Teemperor” Isemann <teemperor at gmail.com>
wrote:

> Just to clarify my point about the “asking if there is already another
> student applying”:
>
> In my situation there is already a student that applied 3 or 4 weeks ago
> and that already has a finished application where I gave multiple rounds of
> feedback and that already landed a few patches that convinced me he’s a
> good candidate. I just told Benson that he can (of course) apply but that
> he might want to see if there is still a project without a student that he
> finds interesting. The reason here is simply that I don’t want Benson to
> spend the remaining time on an application where there is a high chance
> that another student gets selected, while at the same we have useful GSoC
> projects without any applications that end up not happening.
>
> My goal is to have at least one good application for every project we put
> up, as that benefits both LLVM and students.
>
> On Mar 18, 2020, at 10:39 AM, Stefanos Baziotis via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hi to both,
>
> > I'm not applying for GSoC but that's a hint if other students are
> applying to help them get started.
> Yes I agree, thanks for bringing up the topic.
>
> >  On a more serious note, how do I know what issue can be solved in a
> reasonable amount of time/how do I search for one?
>  Well, usually you don't. If you're lucky, someone will be able to provide
> you with some issues that you can get started with in the part of LLVM that
> you're interested
> (independent of GSoC or not). If you can't get such an answer, then one
> thing you can try is search for TODOs and FIXMEs and see if you can tackle
> any of those.
>
> >  He also suggested that I ask if another student has already submitted a
> proposal for this one, and if so, to look for another llvm project within
> the given time remaining.
> In the discussion I posted above, you can see that probably there's
> another person interested.
>
> But of course multiple people can apply to the same project. Realistically
> speaking, you should apply where you think you have a chance, so that you
> can
> devote time that is useful in the end for both parties.
>
> One important thing though is: If you're interested in LLVM, start whether
> you'll get a proposal or not.
> GSoC is good because it motivates people to start contributing to a
> project even if they don't get GSoC in the end. And in the long run that's
> more important (and not only because the next year it will be way easier
> to get a GSoC).
>
> Best,
> Stefanos Baziotis
>
> Στις Τετ, 18 Μαρ 2020 στις 8:51 π.μ., ο/η Benson Bin Bin Li <
> bbl2117 at columbia.edu> έγραψε:
>
>> Ohh also, Raphael Isemann got back to me on the LLDB tab completion
>> project, and said that another student has already written a proposal. He
>> also suggested that I ask if another student has already submitted a
>> proposal for this one, and if so, to look for another llvm project within
>> the given time remaining.
>>
>> On Wed, Mar 18, 2020 at 1:45 AM Benson Bin Bin Li <bbl2117 at columbia.edu>
>> wrote:
>>
>>> IMHO, you do. :)
>>>
>>> Lol, you have too much faith in me. On a more serious note, how do I
>>> know what issue can be solved in a reasonable amount of time/how do I
>>> search for one?
>>>
>>>
>>>
>>>> Please feel free to email me or Ettore if you encounter any blockers,
>>>> or have further questions.
>>>
>>>
>>> Hi Whitney, thanks for the video link and info. I was a bit busy today,
>>> but I will work tomorrow and get back to you on this!
>>>
>>> Best,
>>> Benson
>>>
>>> On Tue, Mar 17, 2020 at 12:54 PM Nicholas Krause <xerofoify at gmail.com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On 3/17/20 10:09 AM, Stefanos Baziotis wrote:
>>>>
>>>> Hi Nick,
>>>>
>>>> What you said makes sense, but it's not called a call graph. :)
>>>>
>>>> Sure I assumed so that was just a term I used by mistake :).
>>>>
>>>> You're essentially referring to what LoopInfo does which makes sense,
>>>> but as I mentioned earlier, this is already done
>>>> in the LoopInfo. Now, how much one will be able to use it in a
>>>> LoopNestPass is another issue, which is certainly
>>>> something that mentors could help you with.
>>>>
>>>> I'm not applying for GSoC but that's a hint if other students are
>>>> applying to help them get started.
>>>>
>>>> Nick
>>>>
>>>>
>>>> Best,
>>>> Stefanos
>>>>
>>>> Στις Τρί, 17 Μαρ 2020 στις 3:35 μ.μ., ο/η Nicholas Krause <
>>>> xerofoify at gmail.com> έγραψε:
>>>>
>>>>>
>>>>>
>>>>> On 3/17/20 9:23 AM, Stefanos Baziotis wrote:
>>>>>
>>>>> > Yes that's correct.
>>>>> Well, now that I saw the LoopNestAnalysis* files, they try to do sth
>>>>> similar. So, I hope it helped.
>>>>>
>>>>> > My idea was similar but using the call graph directly
>>>>>
>>>>> Personally I don't see how the call graph can help you, since well...
>>>>> it's a call graph. :)
>>>>>
>>>>> Not directly but you can could implement a call graph for the loops
>>>>> internal to a function and walk up
>>>>> it backwards. In addition you could make it possible to implement this
>>>>> call graph to know the number
>>>>> of loops nested and pop out to the outermost as a function. Basically
>>>>> SCC for loops themselves rather
>>>>> than functions.
>>>>>
>>>>> That's probably beyond the scope of the project so your right it
>>>>> doesn't matter for this,
>>>>> Nick
>>>>>
>>>>> You care about loops in a specific function. What can help you is the
>>>>> Control-Flow graph, which is basically what LoopInfo uses to identify loops
>>>>> in a function.
>>>>> But because of that, loop identification is not your problem, loop
>>>>> traversing is, if I understand it correctly.
>>>>> Although you have to do things similar to loop identification (i.e.
>>>>> what LoopInfo does) when trying to
>>>>> decide for perfect nestings etc.
>>>>>
>>>>> Best,
>>>>> Stefanos
>>>>>
>>>>>
>>>>> Στις Τρί, 17 Μαρ 2020 στις 3:08 μ.μ., ο/η Nicholas Krause <
>>>>> xerofoify at gmail.com> έγραψε:
>>>>>
>>>>>>
>>>>>>
>>>>>> On 3/16/20 11:41 PM, Stefanos Baziotis wrote:
>>>>>>
>>>>>> Hi everyone,
>>>>>>
>>>>>> >  I probably do not have the time to get a patch through.
>>>>>> IMHO, you do. :)
>>>>>>
>>>>>> First of all, @Benson sorry but I'm not at all familiar with LLDB so
>>>>>> I can't help there.
>>>>>>
>>>>>> Other than that, I'll also disappoint you both probably because I'm
>>>>>> not that familiar with the creation of passes and the problem at hand. I'll
>>>>>> try to help as I can.
>>>>>>
>>>>>> > Is there a specific section of the dragon book that I should read
>>>>>> so that I can at least understand theoretically what it means to create a
>>>>>> LoopNestPass? As I can understand, no because it's more of a structural,
>>>>>> LLVM-specific problem than a generic, compiler optimization problem. > Stefanos
>>>>>> can speak to this more but in order to create a LoopNestPass after reading
>>>>>> what they are talking about requires information from the call graph
>>>>>> > for a function or the loop hierarchy in LLVM IR. I'm not sure of
>>>>>> the internal classes for this so Stefanos is there a way currently to get
>>>>>> the info in IR about
>>>>>> > the outer loop or from the call graph? That seems to be the biggest
>>>>>> problem getting the outer loop in the IR or the call graph. After that you
>>>>>> would
>>>>>> > basically check if the loop is the outer loop and if so you can add
>>>>>> dynamically to the pipeline.
>>>>>>
>>>>>> I'm not sure I followed you here. First of all, if you create a
>>>>>> regular LoopPass, you'll visit loops from the innermost to the outermost.
>>>>>> In the loop nest pass
>>>>>> you want the outermost though, so you'll have to visit them all until
>>>>>> you there. Now if you do it in a function pass, you lose the ability to put
>>>>>> loops
>>>>>> back into the pipeline, as this is how the function pass works. So,
>>>>>> the way I understand it, to solve that problem, one would create something
>>>>>> like a function
>>>>>> pass, figure out the loops there (i.e. with LoopInfo), then convert
>>>>>> it to LoopPass so that you can run loop passes over the loops.
>>>>>> I think this can happen already, but right now, loops are going in
>>>>>> reverse order:
>>>>>> https://github.com/llvm/llvm-project/blob/master/llvm/include/llvm/Transforms/Scalar/LoopPassManager.h#L230
>>>>>> So, maybe if you could modify that to something like
>>>>>> FunctionToLestNestPassAdaptor, it would work? I don't know that's just an
>>>>>> idea, let me not confuse you more.
>>>>>>
>>>>>> Best,
>>>>>> Stefanos
>>>>>>
>>>>>> Yes that's correct. My idea was similar but using the call graph
>>>>>> directly. The other problem is how to keep LCSSA form for all the loops as
>>>>>> well and I'm
>>>>>> aware that function passes don't care about that.  So you can't
>>>>>> really convert to a function pass itself but something similar.
>>>>>>
>>>>>> Nick
>>>>>>
>>>>>> Στις Δευ, 16 Μαρ 2020 στις 5:53 π.μ., ο/η Nicholas Krause <
>>>>>> xerofoify at gmail.com> έγραψε:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 3/15/20 11:12 PM, Benson Bin Bin Li via llvm-dev wrote:
>>>>>>>
>>>>>>> Hi Stefanos,
>>>>>>>
>>>>>>> First, thanks a lot for the very detailed response! I watched both
>>>>>>> of the videos, and I seem to have a rough idea now of how each of the
>>>>>>> different pieces of software maps onto the compilation process. Though I
>>>>>>> found blogs such as these two:
>>>>>>> https://jonasdevlieghere.com/understanding-the-clang-ast/,
>>>>>>> https://releases.llvm.org/2.6/docs/tutorial/JITTutorial1.html to be
>>>>>>> better for a more in-depth understanding. Anyways, in response to your
>>>>>>> answers:
>>>>>>>
>>>>>>> The latter can even be problematic if you start applying C++
>>>>>>>> craziness while the first is pretty much always needed when working in a
>>>>>>>> team project.
>>>>>>>>
>>>>>>> Ok, that makes sense as you would want the style to be consistent
>>>>>>> throughout.
>>>>>>>
>>>>>>> running the LLVM suite is super easy
>>>>>>>>
>>>>>>> Yeah, everything went fine from following your instructions. I do
>>>>>>> have a question though: How do I diagnose failed tests? I found the files
>>>>>>> that correspond to them, and they seem to be 1 line scripts rather than
>>>>>>> "code" per say.
>>>>>>>
>>>>>>> But I think every good GSoC proposal includes a biography-like
>>>>>>>> section
>>>>>>>>
>>>>>>> Then, try to study it, understand the context and the problem.
>>>>>>>>
>>>>>>> But because submitting good patches is one of the best indicators
>>>>>>>>
>>>>>>> Ok, so for the application process, basically try to get more info
>>>>>>> on the projects I am interested in and from there submit a proposal? Given
>>>>>>> the whole coronavirus situation and the time remaining for the application,
>>>>>>> I probably do not have the time to get a patch through. Regarding the
>>>>>>> projects I am interested in, I have narrowed it down to two(mostly because
>>>>>>> I don't think I have the ability to tackle PostDominatorTree project as of
>>>>>>> now), and have the following questions about them:
>>>>>>>
>>>>>>> LLVM Pass
>>>>>>>
>>>>>>>    1. I am following the guide to create a LLVM pass following this
>>>>>>>    guide(https://llvm.org/docs/WritingAnLLVMPass.html), but it
>>>>>>>    appears “add_llvm_library” is a macro and not a built-in command. So I have
>>>>>>>    two questions. 1) In comparing the online repo I found this macro in and my
>>>>>>>    local, it appears I don’t have the file. Do I need to build it then? 2) How
>>>>>>>    do I tell CMake to look for this macro?
>>>>>>>    2. Is there a specific section of the dragon book that I should
>>>>>>>    read so that I can at least understand theoretically what it means to
>>>>>>>    create a LoopNestPass?
>>>>>>>
>>>>>>> Stefanos can speak to this more but in order to create a
>>>>>>> LoopNestPass after reading what they are talking about requires information
>>>>>>> from the call graph
>>>>>>> for a function or the loop hierarchy in LLVM IR. I'm not sure of the
>>>>>>> internal classes for this so Stefanos is there a way currently to get the
>>>>>>> info in IR about
>>>>>>> the outer loop or from the call graph? That seems to be the biggest
>>>>>>> problem getting the outer loop in the IR or the call graph. After that you
>>>>>>> would
>>>>>>> basically check if the loop is the outer loop and if so you can add
>>>>>>> dynamically to the pipeline.
>>>>>>>
>>>>>>> Sorry if I'm not much help as I'm not sure if the call graph API
>>>>>>> supports this but I'm pretty sure LLVM IR doesn't make this easy,
>>>>>>> Nick
>>>>>>>
>>>>>>>
>>>>>>> LLDB Tab Completion
>>>>>>>
>>>>>>>    1. Is there any resource I can read that explains how lldb is
>>>>>>>    able to “pause” the executable and map it to a certain line in the source
>>>>>>>    file/in general how lldb represents the state of the executable?
>>>>>>>    2. Where in the source code can I go to see how existing tab
>>>>>>>    completions are implemented?
>>>>>>>    3. I built lldb and check-lldb, but it seems that the call path
>>>>>>>    to clang got messed up, as it is trying to call "Example=Code/llvm-project"
>>>>>>>    rather than my actual name for the directory "Example-Code/llvm-project".
>>>>>>>    Should I just clone the repo into a parent directory that doesn't use
>>>>>>>    hyphen?
>>>>>>>
>>>>>>>
>>>>>>> (Would it be better if I posted this on the forum?)
>>>>>>>
>>>>>>> Best regards,
>>>>>>> Benson
>>>>>>>
>>>>>>>
>>>>>>> On Sat, Mar 14, 2020 at 11:10 AM Stefanos Baziotis <
>>>>>>> stefanos.baziotis at gmail.com> wrote:
>>>>>>>
>>>>>>>> Hi Benson,
>>>>>>>>
>>>>>>>> You're welcome to the LLVM community!
>>>>>>>>
>>>>>>>> I'll try to help but note that I'm no formal position to talk about
>>>>>>>> how LLVM decides about GSoC (I'm a LLVM newcomer anyway).
>>>>>>>> With that said, the rest is _my_ opinion which is partially formed
>>>>>>>> from my experience as a GSoC student.
>>>>>>>>
>>>>>>>> > But to be up front about this, I have not done any full scale
>>>>>>>> C++ project
>>>>>>>> Depending on how you define "full-scale", a lot of amazing LLVM
>>>>>>>> contributors have not done a full-scale C++. So, I think no problem there,
>>>>>>>> it's just good to have a relatively good knowledge of C++.
>>>>>>>> Talking about C++ skills, I think they're more important if you
>>>>>>>> want to contribute to Clang than say LLVM middle or back-end. Because for
>>>>>>>> Clang, you have to know a lot of details of the language
>>>>>>>> in order to parse it, type-check it and generate LLVM IR. In most
>>>>>>>> other parts of LLVM, you're only using the language.
>>>>>>>> As a matter of fact, if you have a good knowledge of C++, I believe
>>>>>>>> it's more important to be able to understand and adapt to "nearby" code,
>>>>>>>> than to be an expert in C++.
>>>>>>>> The latter can even be problematic if you start applying C++
>>>>>>>> craziness while the first is pretty much always needed when working in a
>>>>>>>> team project.
>>>>>>>>
>>>>>>>> > 1. Do I need to submit a resume/screening/patches?
>>>>>>>> As far as the resume, in the way that you may usually apply to
>>>>>>>> jobs, no. But I think every good GSoC proposal includes a biography-like
>>>>>>>> section
>>>>>>>> where you basically tell your story in programming and how you fit
>>>>>>>> into the project (in our case, LLVM).
>>>>>>>>
>>>>>>>> I'm not sure what you mean by screening.
>>>>>>>>
>>>>>>>> As for patches, I don't think they're required but they're super
>>>>>>>> useful. Not because they're some part of unrelated logistics (like "you
>>>>>>>> have to have X patches to be considered").
>>>>>>>> But because submitting good patches is one of the best indicators
>>>>>>>> (if not the best) that you are able to do useful work in this project. :)
>>>>>>>> And they don't only show your technical skills. But also
>>>>>>>> communication skills, independence etc.
>>>>>>>>
>>>>>>>> > 2. Although I do have interests in certain projects posted on
>>>>>>>> you website(Implement missing tab completion, createLoopPass, and
>>>>>>>> PostDominatorTree), I am uncertain if I have enough expertise to decide
>>>>>>>> what would be an appropriate project to contribute to given my current
>>>>>>>> knowledge and experience.
>>>>>>>> This is kind of a generic sentence.
>>>>>>>> I'd say, start with finding a project that you're truly interested
>>>>>>>> in. Then, try to study it, understand the context and the problem.
>>>>>>>> You don't need to get very far, that's totally ok. You can then do
>>>>>>>> a post (either here or on Discourse:
>>>>>>>> https://llvm.discourse.group/c/community/gsoc/32)
>>>>>>>> for this specific project (you can do posts for multiple projects).
>>>>>>>> Hopefully, by discussing with people (and mentors) and
>>>>>>>> understanding what the project is asking better,
>>>>>>>> you can find if you want to do it or not. Certainly, the mentors of
>>>>>>>> the project can guide you through.
>>>>>>>>
>>>>>>>> 3. The GCC GSoC website suggested checking out their source code,
>>>>>>>> compiling and running their test suite. Can I do something similar for
>>>>>>>> LLVM?
>>>>>>>> Yes, totally. I'm not familiar with GCC internals but running the
>>>>>>>> LLVM suite is super easy (so easy that you don't really learn anything by
>>>>>>>> doing it :P )
>>>>>>>> So, the LLVM project has moved to a common repository:
>>>>>>>> https://github.com/llvm/llvm-project
>>>>>>>> You can clone the project and then use CMake to build it. The cmake
>>>>>>>> configuration for LLVM has a bunch of flags:
>>>>>>>> https://llvm.org/docs/CMake.html
>>>>>>>> and you may get lost. So, I'll say start simple:
>>>>>>>> Go to the llvm-project dir (the one you cloned) and do:
>>>>>>>> cmake ./llvm -DLLVM_ENABLE_PROJECTS="clang"
>>>>>>>> -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON
>>>>>>>> -DLLVM_TARGETS_TO_BUILD="X86"
>>>>>>>>
>>>>>>>> In the link above you can read what the flags do. llvm middle /
>>>>>>>> back-end (i.e. opt / llc, ask if you don't know what these mean) is always
>>>>>>>> built. But to build clang
>>>>>>>> we have to enable it explicitly. We set build type to release
>>>>>>>> because doing a debug build will take a lot of time and a lot of space.
>>>>>>>> Also, when starting out,
>>>>>>>> you probably don't need it. We enable assertions mostly because you
>>>>>>>> can use the -debug option say in opt and see debug prints.
>>>>>>>> Finally, we only build for x86 arch because that's probably what
>>>>>>>> you have and you don't need any other for now.
>>>>>>>>
>>>>>>>> Hit enter and once the configuration is complete you can do:
>>>>>>>> make
>>>>>>>> or
>>>>>>>> make -j<number of threads>    <-- this is faster but limit it
>>>>>>>> depending on your systemS
>>>>>>>>
>>>>>>>> When that's finished, the llvm-project/bin/ dir will have
>>>>>>>> executables like clang, clang++, opt, llc etc.
>>>>>>>> Which you can run (also ask if you don't know what to do with them.
>>>>>>>> With clang you probably will know, it's like invoking
>>>>>>>> most compilers like gcc to compile .c / .cpp files).
>>>>>>>>
>>>>>>>> To run the test suite, you can go to llvm-project/llvm/test and do:
>>>>>>>> <dir of llvm-project>/bin/llvm-lit .
>>>>>>>> That will run only llvm's test suite but you'll get an idea.
>>>>>>>>
>>>>>>>> Also, you can watch these videos:
>>>>>>>> https://www.youtube.com/watch?v=J5xExRGaIIY
>>>>>>>> https://www.youtube.com/watch?v=5kkMpJpIGYU
>>>>>>>>
>>>>>>>> Hope this helped!
>>>>>>>>
>>>>>>>> Kind regards,
>>>>>>>> Stefanos Baziotis
>>>>>>>>
>>>>>>>> Στις Σάβ, 14 Μαρ 2020 στις 2:04 π.μ., ο/η Benson Bin Bin Li via
>>>>>>>> llvm-dev <llvm-dev at lists.llvm.org> έγραψε:
>>>>>>>>
>>>>>>>>> Dear LLVM Team,
>>>>>>>>>
>>>>>>>>> I would like to contribute to/participate in LLVM’s GSOC, because
>>>>>>>>> I would very much like to combine my knowledge of graph theory/algorithms
>>>>>>>>> and my interest in C++ together. Contributing to the LLVM code seems like a
>>>>>>>>> fantastic challenge and learning experience for these two interests of
>>>>>>>>> mine, as well as computer science in general (For example, the use of a new
>>>>>>>>> syntactic category to disambiguate a grammar demonstrates 1) indirection 2)
>>>>>>>>> the power of naming things).
>>>>>>>>>
>>>>>>>>> But to be up front about this, I have not done any full scale C++
>>>>>>>>> project(Although we had to modify the Linux kernel in my OS class, that was
>>>>>>>>> in C). However, I do believe my C++ skills are at an intermediate level, as
>>>>>>>>> C++, like Python, is a language in which I will spend my free time learning
>>>>>>>>> more about. Like vim, there is always more to learn in C++, and to that end
>>>>>>>>> I will watch CppCon Videos or peruse blogs such as Fluent C++(which is a
>>>>>>>>> treasure trove of material to nerd out on) in my free time. I also have a
>>>>>>>>> layman’s knowledge of CMake, from using it to configure ccls to lint C++
>>>>>>>>> code with specific flags, and am aware of Google’s Test framework. Finally,
>>>>>>>>> I am currently taking Professor Stroustrap’s C++ class, and the compilers
>>>>>>>>> course here at Columbia.
>>>>>>>>>
>>>>>>>>> Regarding the logistics:
>>>>>>>>> 1. Do I need to submit a resume/screening/patches?
>>>>>>>>> 2. Although I do have interests in certain projects posted on you
>>>>>>>>> website(Implement missing tab completion, createLoopPass, and
>>>>>>>>> PostDominatorTree), I am uncertain if I have enough expertise to decide
>>>>>>>>> what would be an appropriate project to contribute to given my current
>>>>>>>>> knowledge and experience.
>>>>>>>>> 3. The GCC GSoC website suggested checking out their source code,
>>>>>>>>> compiling and running their test suite. Can I do something similar for LLVM?
>>>>>>>>>
>>>>>>>>> Anyways, thank you for taking the time to read this email, and I
>>>>>>>>> hope to hear back!
>>>>>>>>>
>>>>>>>>> Best regards,
>>>>>>>>> Benson Li
>>>>>>>>> _______________________________________________
>>>>>>>>> LLVM Developers mailing list
>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>>
>>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> LLVM Developers mailing listllvm-dev at lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>> _______________________________________________
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