[LLVMdev] LLVM Parallel IR

[Dounia Khaldi]

Hi William,

Currently, LLVM lowers parallel constructs of OpenMP at the front-end level
to runtime calls; although simple, this ad-hoc solution prevents high-level
reasoning about parallel languages while possibly introducing semantic
inconsistencies in existing sequential program analyses. Worse, users
implicitly rely upon the lack of interprocedural analyses within many
compilers to preserve the semantics of programs even in the presence of
code optimizations.

As part of my PhD work, I worked on introducing a parallel intermediate
representation extension for parallel compilers which I called *SPIRE*.
SPIRE was successfully applied to automatically parallelize sequential
programs within the PIPS source to source compiler. (Here is a link to my
PhD thesis: https://tel.archives-ouvertes.fr/pastel-00935483/document).

As part of my Postdoc work at University of Houston, I am currently
applying SPIRE to LLVM in order to optimize PGAS languages, specifically
OpenSHMEM. The idea is to be able to recognize OpenSHMEM constructs and
represent them explicitly in the LLVM IR using SPIRE to take advantage of
sequential optimizations offered by LLVM. The ultimate goal is to develop
new parallel optimizations based on SPIRE(LLVM IR). The tricky part here is
to prove that the enabled optimizations will generate correct codes. I am
using SPIRE formal operational semantics I developed to prove the
correctness of optimizations performed on parallel programs.

I can send you a submitted paper regarding this work on LLVM if you are
interested.

Best,


-- 
Dounia KHALDI
Postdoctoral Fellow
University of Houston
Department of Computer Science
501 Philip G. Hoffman Hall
Houston, TX  77204-3010

On Mon, Mar 9, 2015 at 10:58 AM, William Moses <wmoses at csail.mit.edu> wrote:

> I'm part of a research group at MIT looking to create an extension of LLVM
> that inherently allows one to nicely code a parallel loop.
>
> Most parallel frameworks tend to take the body of a parallel loop and
> stick it inside of a function for the parallel runtime to call when
> appropriate. However, this makes optimizations significantly more difficult
> as most compiler optimizations tend to be intraprocedural. The goal of this
> parallel IR is to allow LLVM to more easily optimize parallel code -- which
> often gets the short end of the optimization stick.
>
> Long story short: I was wondering if anyone in the LLVM community has
> already begun a similar project or knows of something that begins to
> accomplish this.
>
> Additionally, does anyone who has worked with parallelism in LLVM have any
> specific comments or suggestions regarding this project.
>
> Sincerely,
> William Moses
> MIT Computer Science and Artificial Intelligence Laboratory
>
>
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>


-- 
Dounia KHALDI
Postdoctoral Fellow
University of Houston
Department of Computer Science
501 Philip G. Hoffman Hall
Houston, TX  77204-3010
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