[Openmp-dev] ompparser: A Standalone and Unified OpenMP Parser

[Yonghong Yan via Openmp-dev]

Hi Roger,

Per my understanding, by doing the approach you described, the base
language compiler would need to know the OpenMP syntax, and choose what it
needs the parser to process. It would be hard to make the "parser"
standalone since it depends on what base compilers can do for openmp
parsing.

Right now, ompparser processes a whole line of an omp construct. The
callback mechanism we have in mind, but have not yet fully experiment, is
to let base compiler passes to the ompparser a callback that can parse a
single C/C++/Fortran expression and identifier. For each expression and
identifier that ompparser identifies and separates, the callback would
produce an opaque object associated with string-representation of the
expression/identifier. All the opaque objects for a clause, e.g. "private
(a, b, c)", can be iterated using an iterator provided by the ompparser. In
this approach, two scannings are needed, one by ompparser to tokenize it
and another by compiler to parse it.

Letting the compiler callback to process a list of
identifiers/expressions/array section/range would work as well as long as
the ompparser tells the compiler the stopping character, e.g. ")". This
would need only one scan/parse by the compiler.

Yonghong

On Fri, Sep 27, 2019 at 5:00 PM Roger Ferrer Ibáñez <rofirrim at gmail.com>
wrote:

> Hi,
>
> very interesting development, thanks for sharing it.
>
> Did you consider a more "push-like" approach along with callbacks to
> decouple and ease integration with existing parsers?
>
> This way an existing base language parser (say, hypothetically, clang or
> flang) can push essential tokens that correspond to purely the directive
> syntax (parallel, for, if, nowait, etc.) and then the OpenMP parser could
> tell the base language parser "now parse this part of the language you know
> about".
>
> For instance, parsing a clause like "num_threads(1+2)". clang could push
> tokens "num_threads", "(" and then the OpenMP parser (assuming we are
> deterministic enough!) would let know clang "now parse an expression" which
> would consume 1+2 and pass the expression (possibly opaquely) to the OpenMP
> parser. Lastly clang would push ")" and a full num_threads has just been
> recognized.
>
> To communicate the parser that a part of the OpenMP syntax has been
> recognized (in this case a num_threads clause) I imagine either a callback
> could be used or perhaps the push token function could return a result
> (this is less clear to me, to be honest).
>
> One limitation of this approach would be that the base language still has
> to know some OpenMP syntax bits like "a[lower:size]" for C/C++ depend
> clauses. Declare reduction directive also includes a few special
> identifiers (like omp_priv) that the base language parser may need to be
> told about.
>
> Kind regards,
>
> Missatge de Yonghong Yan via Openmp-dev <openmp-dev at lists.llvm.org> del
> dia dc., 18 de set. 2019 a les 1:26:
>
>> I would like to bring to your attention the ompparser we developed.
>> https://github.com/passlab/ompparser. We have a IWOMP'19 paper for it
>> and the presentation (
>> http://parallel.auckland.ac.nz/iwomp2019/slides_ompparser.pdf) gives you
>> a quick summary of it.
>>
>> Comments are most welcome.
>>
>> Yonghong Yan
>> Associate Professor
>> Department of Computer Science
>> University of North Carolina at Charlotte
>> Office: 410F Woodward
>> Phone: 704-687-8546
>> Email: yyan7 at uncc.edu
>> https://passlab.github.io/yanyh/
>> _______________________________________________
>> Openmp-dev mailing list
>> Openmp-dev at lists.llvm.org
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>>
>
>
> --
> Roger Ferrer Ibáñez
>
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