[llvm-dev] GSoC Opportunity

Sat Mar 14 08:09:48 PDT 2020

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
>
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