[llvm-dev] GSoC Opportunity
Nicholas Krause via llvm-dev
llvm-dev at lists.llvm.org
Sun Mar 15 20:53:07 PDT 2020
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 <mailto: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
> <mailto: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
>
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