llvm dev - Jul 2019 - could you give me some suggestions as to learning llvm?

hello, there.


I am new and very interested in llvm. I have read the language reference,
developer manual, backend guide, tablegen guide, pass guide and other related
materials. and I have started to read the source code of llvm-8.0.1.
I want to write a backend to support part of mips instructions or part of sparc
instructions.

There is few compiler engineerer around me. Could you give me some suggestion?
Thanks in advance!

If I wanna to make it quickly, are there any tips or tutorials(the backend
tutorial on 3.9 is hard to understand)?  Thank you!








sincerely

Jack


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Hi Jack,

There’s a rough learning path to LLVM, both because its intrinsic complexity and
the lack of deep documentation, so I don’t think that a completely new backend
can be produced in a short time. I think that only who have already previous
experience with LLVM could do it. To complicate things, it looks that the few
available documents are scattered down in Google searches, so they are not easy
to find either. The fact that google seems to give different results depending
on your computer settings (starting by language) and your past searching history
does not help to have a consistent experience for all of us.
 
I joined LLVM only 3 months ago, so by no way I am an expert but I managed to
successfully implement a custom LLVM backend as part of a project I am working
on. This is a list of links that I collected over that time that I found useful:

https://jonathan2251.github.io/lbd/index.html
<https://jonathan2251.github.io/lbd/index.html>

https://pdfs.semanticscholar.org/2298/9c214aedc3c58af857d6edc29770c544848c.pdf
<https://pdfs.semanticscholar.org/2298/9c214aedc3c58af857d6edc29770c544848c.pdf>

https://opus4.kobv.de/opus4-fau/files/1108/tricore_llvm.pdf
<https://opus4.kobv.de/opus4-fau/files/1108/tricore_llvm.pdf>

Unfortunately, most of the above is partially outdated, due to the frenetic
stream of changes that LLVM has received over the last few years, but the good
point is that these documents cover some deep aspects that are hardly available
on the official documentation.

I shall also mention that I started by purchasing the  "Getting Started
with LLVM Core Libraries” and “LLVM Essentials” books, but to be honest I
wouldn’t recommend them as I found them to be the least useful resources of all.
The problem is that the authors attempt to cover so much and they ultimately
fail to cover anything properly.

The usual approach is to start from an already implemented (and working) backend
that resembles most the architecture you want to implement. Study a backend by
stepping its source code with a debugger, and create another one according to
your needs. The documents linked above have helped me to understand essential
concepts at times where I got stuck. The positive point of this approach, is
that you don’t necessarily need to understand absolutely everything. You learn
as you go, and as long as you get the concepts right, you will be able to
produce code to your needs and solve all compiler issues specific to your
backend (although not in no time, I’m afraid)

Of course, the LLVM mailing lists are also a source of information and the place
to ask concrete questions. You won’t immediately find all the answers, but in
most cases developers will reply with something that will be useful to you in
order to continue your journey.

So, good luck with your project!

Joan.


> On 25 Jul 2019, at 10:16, 林政宗 via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> hello, there.
> 
> I am new and very interested in llvm. I have read the language reference,
developer manual, backend guide, tablegen guide, pass guide and other related
materials. and I have started to read the source code of llvm-8.0.1.
> I want to write a backend to support part of mips instructions or part of
sparc instructions.
> There is few compiler engineerer around me. Could you give me some
suggestion? Thanks in advance!
> If I wanna to make it quickly, are there any tips or tutorials(the backend
tutorial on 3.9 is hard to understand)?  Thank you!
> 
> 
> 
> 
> sincerely
> Jack
> 
> 
> 
>  
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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