[llvm-dev] Want to contribute in LLVM.

Tue Dec 15 18:42:44 PST 2020

Hey Amit,

EECS583 at Umich also has a homework assignment or two that you could give
a go if you wanted.
HW2 asks you to extend the loop invariant code motion pass and do frequent
path LICM (hoist almost invariant code).

Link below.
https://web.eecs.umich.edu/~mahlke/courses/583f18/homeworks.html

It's just another resource.

Best of luck.

Regards,

Armand

On Tue, Dec 15, 2020 at 4:18 PM Stefanos Baziotis via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Amit,
>
> There are the bugs tagged beginner but last time I checked, IMHO, they
> were not that "beginner-friendly" after all.
>
> The way I would recommend that you start with LLVM is by rewriting a pass.
> One thing to note here is that this is not really a contribution (i.e.
> a commit won't result immediately from that), so if you're only interested
> in contributing something with your first try, that won't do it.
>
> But a common theme I see among beginners, including myself when I started,
> is that when you're obsessed with landing a commit,
> unavoidably you're going to "hack your way towards it". That basically
> means that you'll just gather relatively shallow knowledge, maybe
> with some breadth, but that limited too, just to commit something. That's
> bad and it will probably not serve you in the long run.
>
> This is why for example, in courses which use LLVM as a teaching tool, the
> assignments don't ask you to do something
> shallow like that but instead they ask for something that requires some
> kind of deep knowledge and thought (which you develop along).
>
> To that end, I recommend rewriting a pass (which is btw somewhat common in
> courses). Now, that might sound scary but it's not.
> The _actual_ goal is not to actually rewrite the pass. Neither all of it,
> nor at the production level of LLVM. Rewriting
> the pass is just an "artificial goal" only to have something to move
> towards. The _actual_ goal is what you'll learn by moving
> towards this goal. And what you'll learn will probably be both deep and
> broad.
>
> You only need to start simple, like "OK, how do I query this analysis?".
> Just that, then you try something like "hmm, how can I inspect / traverse
> the results of this analysis" etc. (and the good thing is that for a lot
> of these first steps, multiple other passes will have done the exact
> same thing and you should feel free to copy code shamelessly as you're
> starting out).
>
> After some time doing that, you'll find that you start understanding the
> system in some detail and _then_, you'll be equipped to do actual commits.
>
> Now, the question is with which pass to start with? Again, because of the
> above, that doesn't really matter, but in any case, it depends on what you
> like.
> For example, if you're interested in loops, I'd start with LCSSA (and
> along with it, I'd give a try to the LLVM Loop Terminology). If you're
> interested
> in inter-procedural optimizations, I'd start with Sparse Conditional
> Constant Propagation (SCCP).
>
> If you have no idea where to start or what you like, you might start with
> Scalar Replacement of Aggregates (SROA), just because I saw it
> in a cool course on UIUC recently and it seems to guide you relatively
> well. Here's the link:
> http://misailo.web.engr.illinois.edu/courses/526-sp20/,
> it's project 1 (again, don't need to even do the whole thing, do the parts
> that motivate you; I mean please don't treat that as an _actual_ assignment,
> you probably have enough of those already :) ).
>
> So, this got very long, sorry for that, I hope it helps. Please don't
> hesitate to reach me for questions.
>
> Best,
> Stefanos
>
> Στις Τρί, 15 Δεκ 2020 στις 9:12 μ.μ., ο/η amit kumar via llvm-dev <
> llvm-dev at lists.llvm.org> έγραψε:
>
>> Respected Sir/Ma'am,
>>                        I'm Amit Kumar, a 3rd-year undergraduate
>> student in Computer Science Engineering (CSE) from IIIT Nagpur, India.
>> I am new to open source only contributed to HactoberFest in the past 2
>> years and I came across LLVM through GSoC and interested in
>> building some new features in the newer version's LLVM and contribute
>> to the language. I had studied Compiler Design in our courses.
>>
>> Please help me and show me direction towards starting my journey to
>> the open-source contribution.
>> Thanks and Regards
>> Amit Kumar
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
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