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Created by Ondřej Čertík@certikOwner88 of 102 checklist items completed88/102 checklist items

MVP: Roadmap to compile the SNAP project

The roadmap at #272 is a general roadmap. In this issue I am listing a specific roadmap to compile just one project:

https://github.com/lanl/SNAP

Once we can compile it, we can release an MVP (minimum viable product) of LFortran. This project is a great target for MVP because it is not written by me, thus this will be useful to people, it uses Fortran 95, it's about 8000 lines of code, and the MPI can be turned off, it is a proxy app for a bigger production code. It is within reach. To compile it, we do not need to implement Fortran features in all generality, just enough to compile SNAP.

Roadmap

Parsing and AST now works. We are now working on ASR, see below.

Parsing

There are only 4 small issues, otherwise LFortran can parse everything.

LFortran issues:

SNAP seems to be using two extensions, which might be fixed in SNAP itself, or we can implement them in LFortran:

AST

We can test that AST is correct file by file using lfortran fmt -i analyze.f90 which overwrites the file by going from AST to source code. At this point the LFortran master can translate all files to AST and back and the result compiles with gfortran and SNAP gives identical results. This ensures that there are no major bugs in the parser and the AST representation (there might still be some minor bugs where we got the right result by accident). Here are all the files sorted from the largest to the smallest:

ASR

The goal is to compile each module to the modfile using lfortran -c global.f90 -o global.o. Here is the first full dependency tree, we can take it from top to bottom:

  • global.f90
  • version.o : global.o
  • geom.o : global.o
  • sn.o : global.o
    • allocatable attribute for array declarations (module variable)
  • data.o : global.o
  • control.o : global.o
  • time.o : global.o
  • plib.o : global.o time.o
  • thrd_comm.o: global.o plib.o
  • expxs.o : global.o geom.o sn.o data.o
  • solvar.o : global.o plib.o geom.o sn.o data.o control.o
  • mms.o: global.o geom.o sn.o data.o control.o plib.o
    • Generic procedures from the plib module (#358 (closed))
    • "LFortranException: read_string: String is too short for deserialization", probably due to derived types
  • dealloc.o : global.o sn.o data.o mms.o geom.o solvar.o control.o
  • utils.o : global.o dealloc.o plib.o control.o
  • analyze.o: global.o control.o geom.o data.o solvar.o plib.o
  • input.o : global.o plib.o geom.o sn.o data.o control.o utils.o time.o
  • setup.o : global.o geom.o sn.o data.o control.o mms.o utils.o time.o plib.o
  • output.o : global.o geom.o sn.o data.o control.o utils.o solvar.o mms.o time.o plib.o
  • snap_main.o : global.o utils.o version.o input.o setup.o output.o time.o dealloc.o plib.o control.o
  • dim1_sweep.o : global.o geom.o sn.o data.o control.o plib.o
  • dim3_sweep.o : global.o plib.o geom.o sn.o data.o control.o thrd_comm.o
  • mkba_sweep.o : global.o plib.o geom.o sn.o data.o control.o thrd_comm.o
  • octsweep.o : global.o geom.o sn.o data.o control.o solvar.o thrd_comm.o dim1_sweep.o dim3_sweep.o mkba_sweep.o
  • sweep.o : global.o data.o geom.o sn.o control.o octsweep.o solvar.o plib.o thrd_comm.o
  • inner.o : global.o geom.o sn.o data.o control.o solvar.o sweep.o time.o plib.o thrd_comm.o
  • outer.o : global.o geom.o sn.o data.o solvar.o control.o inner.o time.o plib.o expxs.o thrd_comm.o
  • translv.o : global.o plib.o geom.o sn.o data.o control.o utils.o solvar.o expxs.o outer.o time.o thrd_comm.o analyze.o

Other issues to resolve:

  • Runtime library must be working

The LFortran and SNAP commits that together produce an ASR for snap_main.f90:

Fortran features that were commented out in SNAP that we need to implement in LFortran:

  • format statement
  • do loops with no loop variable (just do / code / end do)
  • where statement
  • improve derived types: we have an initial implementation, but we need to improve it for SNAP
  • namelist
  • array initializer
  • case statement for strings
  • improve pointers: add nullify, fix bugs
  • improve open statement
  • runtime library functions: huge, all, mod, minloc, ceiling, maxloc, get_command_argument, adjustl, exit, date_and_time

The SNAP branch compiles with gfortran into an executable, and runs with an output:

$ ./gsnap 
 Aww SNAP. Program failed. Try again.

The parts that were commented out make the code not run correctly, but it "runs".

Backends

C++

The C++ backend (as of the latest master 93d2b868) generates the following code:

It does not compile with a C++ compiler yet. This is our main effort now.

LLVM

Other issues

Edited by Ondřej Čertík