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digitalmars.D.ldc - GSoC'19: Any LLVM based idea? If not let's think one!

reply Reshabh Sharma <reshabhsh gmail.com> writes:
Hello,

I'm Reshabh Sharma, a senior year undergrad from India. I 
completed my last GSoC'18 successfully with LLVM 
(http://blog.llvm.org/2018/09/integration-of-libc-and-openmp-packages.html).

I was always interested in compilers, but the last GSoC and LLVM 
dev meeting have given it a different shape!

These days I'm working on a patch on a Global Instruction 
Scheduler in the optimization phase of LLVM and got another 
project on Alias Analysis in LLVM from the start of next year in 
todo list.

LDC uses LLVM as back-end, I would be happy if you have some 
LLVM/compiler related stuff in wishlist that I can do with D lang 
this GSoC'19.

Some specific IR passes for D or anything more at the backend 
side, it will help me to become a better compiler engineer (that 
I aim to become).

I would be glad to see some core compiler/llvm based ideas 
floating and would be very happy if someone is ready to mentor me 
for this GSoC.

Best,
Reshabh Sharma
Dec 12 2018
parent reply Johan Engelen <j j.nl> writes:
On Wednesday, 12 December 2018 at 17:57:20 UTC, Reshabh Sharma 
wrote:

 I would be glad to see some core compiler/llvm based ideas 
 floating and would be very happy if someone is ready to mentor 
 me for this GSoC.


I'm not sure whether I have the time to mentor, but some ideas 
that involve LDC and LLVM :

- exploiting immutability of variables (notably of structs such 
as string slices)
- devirtualization
- improve debuginfo
- ASan with GC and multithreading
- function multiversioning

Browsing our issue tracker on Github helps. There are a number of 
ideas posted there.

With which organisation would you submit your idea? (For LDC, you 
should contact Dlang foundation)

-Johan
Dec 12 2018
next sibling parent reply Reshabh Sharma <reshabhsh gmail.com> writes:
On Wednesday, 12 December 2018 at 22:50:16 UTC, Johan Engelen 
wrote:

 On Wednesday, 12 December 2018 at 17:57:20 UTC, Reshabh Sharma 
 wrote:



 - exploiting immutability of variables (notably of structs such 
 as string slices)
 - devirtualization
 - improve debuginfo
 - ASan with GC and multithreading
 - function multiversioning

 Browsing our issue tracker on Github helps. There are a number 
 of ideas posted there.


I might be interested in working in Devirtualization 
https://github.com/ldc-developers/ldc/issues/1828


 With which organisation would you submit your idea? (For LDC, 
 you should contact Dlang foundation)


I am planning to work with Dlang this GSoC, I told my interests 
to  Michael Parker and he directed me to ask in LDC forum.

Thanks,
Reshabh Sharma
Dec 12 2018
parent Johan Engelen <j j.nl> writes:
On Thursday, 13 December 2018 at 06:10:55 UTC, Reshabh Sharma 
wrote:

 I might be interested in working in Devirtualization 
 https://github.com/ldc-developers/ldc/issues/1828


See also: https://github.com/ldc-developers/ldc/pull/2397
Dec 13 2018
prev sibling parent reply Johan Engelen <j j.nl> writes:
On Wednesday, 12 December 2018 at 22:50:16 UTC, Johan Engelen 
wrote:

 - exploiting immutability of variables (notably of structs such 
 as string slices)
 - devirtualization


Btw, I think these are somewhat similar and that the first may 
lead to larger performance gains. Once the first works, the 
second follows almost automatically (after a deeper study of D 
language semantics of object runtime type).

-Johan
Dec 13 2018
parent reply Reshabh Sharma <reshabhsh gmail.com> writes:
See also: https://github.com/ldc-developers/ldc/pull/2397


On Thursday, 13 December 2018 at 19:17:15 UTC, Johan Engelen 
wrote:

 On Wednesday, 12 December 2018 at 22:50:16 UTC, Johan Engelen 
 wrote:

 - exploiting immutability of variables (notably of structs 
 such as string slices)
 - devirtualization


 Btw, I think these are somewhat similar and that the first may 
 lead to larger performance gains. Once the first works, the 
 second follows almost automatically (after a deeper study of D 
 language semantics of object runtime type).


Thanks, I don't have much knowledge about this so I'll go with 
your words :) then I would insist that we can have "exploiting 
immutability of variables" as a project idea.

Can you please suggest some resources for getting a bit more idea 
about how others have exploited immutability of variables or is 
there a generic term for this (I could not find much online :/ ).

I can help in drafting a project idea for this and if it could 
get a mentor then I'm willing to be the part (If I qualify to be) 
else it will definitely catch some eyes!

Best,
Reshabh Sharma
Dec 15 2018
parent reply Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Saturday, 15 December 2018 at 19:52:42 UTC, Reshabh Sharma 
wrote:

See also: https://github.com/ldc-developers/ldc/pull/2397


 On Thursday, 13 December 2018 at 19:17:15 UTC, Johan Engelen 
 wrote:

 On Wednesday, 12 December 2018 at 22:50:16 UTC, Johan Engelen 
 wrote:

 - exploiting immutability of variables (notably of structs 
 such as string slices)
 - devirtualization


 Btw, I think these are somewhat similar and that the first may 
 lead to larger performance gains. Once the first works, the 
 second follows almost automatically (after a deeper study of D 
 language semantics of object runtime type).


 Thanks, I don't have much knowledge about this so I'll go with 
 your words :) then I would insist that we can have "exploiting 
 immutability of variables" as a project idea.

 Can you please suggest some resources for getting a bit more 
 idea about how others have exploited immutability of variables 
 or is there a generic term for this (I could not find much 
 online :/ ).


(In case you haven't seen it (C++ devirtualisation) 
https://www.youtube.com/watch?v=Dt4UehzzcsE&index=36&list=PL_R5A0lGi1AARZysSx
VzpaLAzny4es2e&t=0s )

Unlike C++ where const isn't any good for optimisation, in D an 
immutable variable will never change and immutable is transitive: 
no mutable references to it are allowed, only const (which is a 
guarantee to not change the data through this reference) and 
immutable, neither of which may be used to change the value _or 
anything reachable from it_.
As a consequence of this not only can you safely cache the value 
and any values derived from it, the data referenced by an 
immutable pointer will never alias mutable data (it may alias 
const data but if it does then that data is immutable so it will 
never change).

The devirtulisation then follows from the fact that the vtable is 
immutable and assigned once in construction (unlike C++).


 I can help in drafting a project idea for this and if it could 
 get a mentor then I'm willing to be the part (If I qualify to 
 be) else it will definitely catch some eyes!


If you're having trouble finding a mentor, I could do it.
Dec 15 2018
next sibling parent reply Johan Engelen <j j.nl> writes:
On Sunday, 16 December 2018 at 05:59:37 UTC, Nicholas Wilson 
wrote:

 On Saturday, 15 December 2018 at 19:52:42 UTC, Reshabh Sharma 
 wrote:

 I can help in drafting a project idea for this and if it could 
 get a mentor then I'm willing to be the part (If I qualify to 
 be) else it will definitely catch some eyes!


 If you're having trouble finding a mentor, I could do it.


I probably won't be able to full-time mentor this. But I do want 
to be involved as I've already been working on it.

(Don't forget that working on AddressSanitizer for our GC and 
fibers would also be pretty cool)

-Johan
Dec 22 2018
parent Reshabh Sharma <reshabhsh gmail.com> writes:
On Saturday, 22 December 2018 at 17:10:12 UTC, Johan Engelen 
wrote:


 I probably won't be able to full-time mentor this. But I do 
 want to be involved as I've already been working on it.


No worries, I would be happy to keep you updated with the 
progress!



 (Don't forget that working on AddressSanitizer for our GC and 
 fibers would also be pretty cool)


I'm up to any cool compiler related stuff these days ;) Let's 
then more formally define a skeleton for the project, as it would 
be easier for me to go through the literature supporting the 
project.


Best,

Reshabh Sharma
Jan 05 2019
prev sibling parent Reshabh Sharma <reshabhsh gmail.com> writes:
On Sunday, 16 December 2018 at 05:59:37 UTC, Nicholas Wilson 
wrote:


 If you're having trouble finding a mentor, I could do it.


Sorry for the late reply! I got super engaged in project 
submissions and the much awaited holidays ^_^

Thanks  nicholas for showing interest in mentoring, are you still 
interested? I will be happy to work on this :)

Best,

Reshabh Sharma
Jan 05 2019