llvm dev - May 2021 - LLVM COBOL front end question [Re: A friendly question]

> I think there are a bunch of somewhat conflated here and it's probably
> worth unpicking them a bit.  They seem to be:
> 
>   - Is anyone interested in writing a COBOL front end for LLVM?
>   - Would a COBOL front end be considered for integration with the LLVM
> repository?
>   - Would projects to work on an LLVM COBOL front end be considered for
> the GSoC or similar?
Actually my first reaction was, retarget gnucobol to emit LLVM IR instead
of C, and run the LLVM backend on it.  (I'd speculated to myself about
doing this as a fun post-retirement project.)  There's probably licensing
questions to resolve there first.  I could see compilation speed getting
better as a result, although runtime performance is unlikely to be better
than routing through C.  Not clear what the effect would be on debugging;
it looks like there are a couple of packages out there that let you debug
COBOL using the existing gnucobol setup, and gdb doesn't understand COBOL
so if anything the debugging situation is likely to get worse.

I've retargeted a COBOL front-end in the past (not to LLVM), and I'd
estimate that it is significantly more work than one GSoC project.
(Not that I've actually looked inside gnucobol to see how it works.)

As for who's interested in a COBOL front-end:
The OpenVMS people (vmssoftware.com) are definitely headed in the direction 
of a native LLVM-speaking COBOL frontend, although I'm sure it would remain
proprietary.  That direction would presumably include adding DIBuilder 
features for the COBOL data types, and getting LLVM to emit the proper DWARF 
descriptions.  Haven't seen any signs of that happening upstream, though.

--paulr

On 5/6/2021 11:21 AM, paul.robinson at sony.com wrote:
>
> As for who's interested in a COBOL front-end:
> The OpenVMS people (vmssoftware.com) are definitely headed in the direction
> of a native LLVM-speaking COBOL frontend, although I'm sure it would
remain
> proprietary.  That direction would presumably include adding DIBuilder
> features for the COBOL data types, and getting LLVM to emit the proper
DWARF
> descriptions.  Haven't seen any signs of that happening upstream,
though.
>
> --paulr
>
Yes, we have our Digital legacy COBOL frontend hooked to LLVM.  That
frontend generates our legacy GEM IR which is then converted to LLVM IR.
It is currently an Itanium-hosted cross-compiler but we're bootstrapping
our compilers to native OpenVMS x86 right now (we have clang "working"
on OpenVMS x86 on Virtual Box today).

The frontend (and much of the companion library to process the DEC4/DEC8
datatypes) still has Digital copyrights which are own owned by HPE and
licensed to us.  I would be unable to opensource it without their
permission.  And you'd get a nice vintage COBOL 85 compiler written in
BLISS. :) :) :)

As for the DIBuilder COBOL support, since our cross-compilers are based
on an ancient LLVM 3.4.2 (due to the ancient Itanium C++ we have on our
host systems), we have to refresh all of that with our native
bootstrapping before I could even consider upstreaming any of that.  And
we are just starting on our symbolic debugger so I don't know if
anything we've done even works yet.  And I haven't even explained level
88 condition names to the debugger engineers yet. :)

For those keeping score at home, what we have so far is our legacy
compilers for BASIC, BLISS, C, COBOL, Fortran95, Macro-32 VAX assembly,
and Pascal.  All but BASIC are in good shape.  BASIC and its RTL do some
un-natural acts.  And now we just bootstrapped clang 10 (we had to pick
something to start) by compiling on Linux using a mixture of OpenVMS and
Linux headers and then moving the objects to OpenVMS for linking (using
the OpenVMS linker of course).



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