Thanks, Martin. We expect it to be a medium size project. And we will be
sure that Ethan can build, test, and debug the GNAT-FE and other GCC
components.
Take care,
-Tuck
On Mon, Mar 24, 2025 at 7:23 PM Martin Jambor <mjam...@suse.cz> wrote:
> Hello,
>
> in general the project proposal looks very good. A few comments inline:
>
> On Tue, Mar 18 2025, Tucker Taft via Gcc wrote:
> >
> [...]
> > The GNAT front end is organized into three basic phases, a parser, a
> > semantic analyzer, and an expander. In the sources, these are
> represented
> > by source files par-ch*.adb, sem_ch*.{ads,adb}, and exp_ch*.{ads,adb},
> > where "ch*" is short-hand for the various chapters of the Ada reference
> > manual. For this project the intent is to augment primarily the "chapter
> > 5" components, given that loop and parallel-do statements are defined in
> > chapter 5 of the Ada reference manual. For example, the function
> > Par.Ch5.P_Loop_Statement is where most of the parsing of the loop
> statement
> > takes place, while Par.Ch5.P_Parallel_Do_Statement would be a new local
> > function of Par.Ch5. Similarly, Sem_Ch5.Analyze_Loop_Statement would be
> > augmented, while Sem_Ch5.Analyze_Parallel_Do_Statement would be new. And
> > finally, Exp_Ch5.Expand_Loop_Statement would be augmented, while
> > Exp_Ch5.Expand_Parallel_Do_Statement would be new.
> >
> > The project would begin with the parser, simply recognizing the new
> syntax,
> > and producing debug output to report on whether the parse was successful.
> > The next phase would be to construct the appropriate tree
> representations,
> > which would mean updating the gen_il* set of files to include new fields
> > and node types to support the parallel for-loop and parallel do
> statement.
> > As part of doing this, pseudo-code would be developed for the semantic
> and
> > expansion phases, to ensure that the new tree components created meet the
> > needs of these later phases. Finally the semantic and expansion phases
> > would be implemented in Ada, using the new tree components available.
> >
> >
> > For the expansion phase, the job is primarily to transform the syntax
> into
> > the appropriate calls on out-of-line runtime components providing
> > light-weight-thread management. These routines have already been
> developed
> > and debugged, and are available on the GitHub site for the ParaSail
> > parallel programming language (
> > https://github.com/parasail-lang/parasail/tree/main/lwt).
> >
> > As far as effort involved, the parsing functions in the GNAT Front End
> tend
> > to be quite short, often less than a page of code, making heavy use of
> > shared parsing components. The semantic phase tends to be significantly
> > more complex, but for this effort relatively little additional code will
> be
> > required, because the additional static semantics for these new features
> > are pretty simple. The major effort will be in the expansion phase,
> > primarily because the out-of-line light-weight-threading library expects
> > the loop body to be represented as a procedure. In fact the GNAT-FE
> > frequently creates simple out-of-line routines as part of implementing
> > certain existing Ada features, so there should be plenty of models to
> work
> > from to turn the loop body into an out-of-line routine. Similarly,
> > generating calls to run-time routines is also quite common as part of
> > various GNAT-FE expansion routines, so we can use those as models as
> well.
> >
> >
> > One feature of the light-weight-threading library we will be interfacing
> > with is that it sits on top of the existing Ada runtime, as well as the
> GCC
> > implementation of OpenMP, without any need to alter these underlying
> > components.
> >
> > Overall we would estimate a couple of weeks for the parsing and initial
> > semantic analysis for these two features, with the bulk of the summer
> spent
> > on the expansion phase, finalizing the semantic analysis, and if there is
> > time, working on error recovery.
>
> Do you envision this as a medium-sized (approx. 175 hours) or large (350
> hours) project?
>
> >
> > As far as mentors, Tucker Taft had agreed to be a mentor. Tucker was the
> > lead designer of Ada 2022, and has implemented the light-weight-threading
> > library that we will be interfacing with. Richard Wai has also agreed to
> > be a mentor. Richard is an active member of the ISO-WG9 committee on Ada
> > and its Ada Rapporteur Group (ARG), and has also made contributions to
> GCC
> > components, in particular the GNAT front end, in the past.
> >
> > The contributor will be Ethan Luis McDonough. Ethan is currently
> finishing
> > his last semester in the Penn State University online Software
> Engineering
> > program, and is also finishing up an internship at the Lawrence Livermore
> > Laboratory focused on open source LLVM development. Ethan spent his time
> > at the lab working on LLVM’s Fortran frontend as well as GPU
> > instrumentation tools. Most recently Ethan has been implementing a code
> > generator for a hardware description language built on top of the
> ParaSail
> > Programming Language, using an API he implemented in Ada providing access
> > to the tree representation used by the ParaSail front end (which is
> written
> > in Ada). He looks forward to making a contribution to the open-source
> GNAT
> > FE component of the GCC compiler collection.
>
> That definitely looks like solid experience that proves that Ethan has
> what it takes to work on the project. Still, the general rules apply,
> please look at the "Before you apply" section of our GSoC page at
> https://gcc.gnu.org/wiki/SummerOfCode#Before_you_apply and make sure you
> are able to build, install, test and debug GCC. I am not familiar with
> Ada FE myself but in this instance finding the correct dumps but also to
> get a gdb session going and inspect the compiler internals from within.
>
> Good luck!
>
> Martin
>
