Re: GSoC

[Thomas Schwinge <tschwinge@baylibre.com>]

Hi Abhinav!

Thanks for your interest in contributing to GCC, and thanks to Martin for
all the information you already provided.  Just a bit more, to get you
started on developing a proper project proposal:

On 2024-03-13T14:54:52+0100, Martin Jambor <mjambor@suse.cz> wrote:
> On Tue, Mar 12 2024, Abhinav Gupta wrote:
>>     I looked at all the links you provided in the reply and read the
>> paper cited on the GCC page for GSoC. I also looked into the rust
>> frontend project during this time, and the Offloading project
>> interests me more, so I will focus solely on it in the remaining seven
>> days before the deadline for GSoC application submission.
>
> AFAIU, in five days (from now) the application period *opens*, the
> deadline is 2nd April.  Still it is good idea not to lose any time.

Indeed, no rush yet.  :-)

>> Are there other resources I can look at to better understand the whole
>> process?

At some point, no too late, you should spend some time on learning how to
build GCC, and run the test suite.
<https://gcc.gnu.org/wiki/SummerOfCode> and
<https://gcc.gnu.org/wiki/#Getting_Started_with_GCC_Development> have
some pointers to get started.  If you have specific questions, we're
happy to help, of course.

>> Reading the git commit on the website is proving to be very
>> slow.

Yes, that's not going to be necessary.

>> I think the git commit about Intel MIC would be like a
>> "template" in loose terms

Right, that's in fact a very good description.  The idea here is not to
bring back the whole Intel MIC emulator, but something very much simpler.

>> to implement the host-ISA mode at least, but
>> for the libgomp plugin, I need a better understanding.

Find existing libgomp plugins as 'libgomp/plugin/plugin-*.c'.  The
'GOMP_OFFLOAD_[...]' functions implement the entry points, the offloading
plugin API.  Actually also the very simple 'libgomp/oacc-host.c' should
be helpful.  That's essentially the API you need to care about (for
OpenACC; but OpenMP 'target' also won't require much more, for a start).

Make some thoughts (or actual experiments) about how we could
use/implement a separate host process for code offloading.

And otherwise, as Martin said:

> You need to understand how OpenMP programs are internally represented.
>
> Look at the following (hopefully correct, at least as long as you try it
> on a system without any Offloading enabled) simple testcase for OpenMP
> target construct:
>
> ----------------------------------------------------------------------
> #include <stdio.h>
>
> volatile int v = 1;
>
> int main (int argc, char **argv)
> {
>   int i = v;
>
> #pragma omp target map(to:i)
>   {
>     printf ("OpenMP target hello world, i is: %i\n", i);
>   }
>
>   return 0;
> }
> ----------------------------------------------------------------------
>
> and compile it with:
>
>   gcc -fopenmp omptgt-hello.c -O2 -fdump-tree-optimized
>
> and then look at the generated optimized dump.  This should give you an
> idea how OpenMP regions are internally represented (as outlined
> functions) and how calls into libgomp, the run-time library doing a lot
> of the magic, look like.
>
> You can try to do more similar exercises with more OpenMP testcase which
> you can find in sub-directory libgomp/testsuite/libgomp.c of in the GCC
> repository.
>
> And then you should perhaps have a look into libgomp itself (you'll find
> it in libgomp sub-directory) how GOMP_target_ext is implemented - though
> don't worry if you don't understand many of the details, it is complex
> stuff.  At this point hopefully more of the contents of the Offloading
> wiki page will make sense.
>
> Again, ask on the mailing list if you have any specific questions.


Grüße
 Thomas


>> On Thu, 7 Mar 2024 at 20:37, Martin Jambor <mjambor@suse.cz> wrote:
>>>
>>> Hello,
>>>
>>> On Wed, Mar 06 2024, Abhinav Gupta via Gcc wrote:
>>> > Dear GCC Community,
>>> >     I hope this email finds you well. My name is Abhinav Gupta. I am a
>>> > 3rd-year student at IIT Tirupati pursuing a bachelor's degree in
>>> > computer science and engineering. I am writing to express my interest
>>> > in contributing to the GCC project under GSoC.
>>>
>>> We are very happy that you find contributing to GCC interesting.
>>>
>>> > I am interested in two projects - Offloading to a separate process on
>>> > the same host, I am already working in parallel computing,
>>> > specifically parallelising tensor algorithms using various techniques
>>> > as part of my research project at IIT Tirupati. Although this is not
>>> > directly related to compilers, I will be able to get going with the
>>> > project quickly.
>>>
>>> I'd personally very much like to see this project implemented.  There is
>>> a lot of information on offloading at
>>> https://gcc.gnu.org/wiki/Offloading
>>>
>>> To give you a bit more context where the idea comes from, it was first
>>> thought of in email thread starting with
>>> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/603984.html and
>>> the patch that was "scrubbed" from the email archive eventually became
>>> commit
>>> https://gcc.gnu.org/cgit/gcc/commit/?id=e4cba49413ca429dc82f6aa2e88129ecb3fdd943
>>>
>>> I hope these pointers will further help help you find out where to look
>>> when planning the project.  If you need more help, please feel free to
>>> ask (I'm CCing Thomas who then is perhaps best placed to answer).
>>>
>>> > The second project is Rust Front-End - both the BIR location support
>>> > and rustc testsuite adapter are of interest to me,
>>>
>>> Please note that Rust-GCC projects are a bit special in the sense that
>>> they are often discussed primarily on Zulip of the gcc-rust team:
>>>
>>> https://gcc-rust.zulipchat.com/
>>>
>>> So you may want to reach out to them there as well.
>>>
>>> > having worked on
>>> > compiler front ends as part of my college's compiler design course
>>> > combined with my experience in working with large libraries written in
>>> > C++ (such as CTF) I believe that these two projects are something that
>>> > I can do.
>>>
>>> You seem to be quite ready!
>>>
>>> >
>>> > Proposed Timeline:
>>> > I can start working as soon as my end-semester exams finish, i.e. 9th
>>> > May 2024, and continue to work for however long it requires me to
>>> > complete the project.
>>> > Week 1-2 -> Knowing the existing code and understanding how it works.
>>>
>>> Right, but please try to do a bit of this, at least on the high level,
>>> also now when preparing the proposal.  There will be lots to learn in
>>> the first weeks even so.  Mainly because...
>>>
>>> > Week 3-8 -> Working on the implementation of whichever project we
>>> > decide to move forward with
>>> > Week 9-12 -> Testing and creating understandable documentation for the same.
>>> >
>>> > This is a very rough timeline,
>>>
>>> ...eventually the milestones in the application will have to be more
>>> specific, mainly to demonstrate you have basic understanding of the
>>> proposed project.
>>>
>>> > and I will refine it further as we
>>> > discuss the project idea. This email is more of a call for guidance
>>> > than an application, and I would appreciate any feedback you give me.
>>>
>>> This is a very good start.
>>>
>>> Good luck!
>>>
>>> Martin