[LLVMdev] [RFC] WebAssembly Backend

[Chandler Carruth]

On Wed, Jun 17, 2015 at 12:24 PM Hal Finkel <hfinkel at anl.gov> wrote:

> ----- Original Message -----
> > From: "Dan Gohman" <dan433584 at gmail.com>
> > To: llvmdev at cs.uiuc.edu
> > Sent: Wednesday, June 17, 2015 11:16:21 AM
> > Subject: [LLVMdev] [RFC] WebAssembly Backend
> >
> > Hello all,
> >
> > WebAssembly [0] its a new virtual ISA being designed to efficiently
> > run compiled code in web browsers and other things, starting with
> > C/C++, and eventually many other languages [1]. WebAssembly
> > distinguishes itself from other virtual ISAs with optimizations to
> > reduce download size and decode time, strong portability and
> > predictability invariants (for example, the base has no undefined
> > behavior in the C/C++ sense), and participation from several browser
> > vendors.
> >
> > We're interested in developing and contributing an LLVM backend to
> > target this new ISA. There are many interesting technical aspects
> > that
> > we’re excited to discuss with the LLVM community. Before we get
> > started though, we need to figure out how to do our development. Most
> > backends in LLVM were initially submitted in monolithic form and
> > developed incrementally thereafter. However, we have contributors
> > from
> > multiple organizations, and a monolithic patch wouldn’t accurately
> > reflect the separate contributions.
> >
> > Would the LLVM community be willing to let us start a new target from
> > scratch within the LLVM tree, following normal LLVM
> > incremental-development practices? The target would naturally start
> > as
> > "experimental", excluded from the default build. The code
> > organization
> > would look like any other backend, with everything under
> > lib/Target/WebAssembly except for various bits of configury that any
> > backend needs. We have need of the functionality provided by
> > SelectionDAG, MI and others, so this will pretty clearly be a
> > backend,
> > rather than a specialized serialization. Also, the people leading the
> > project are JF Bastien and Dan Gohman, existing LLVM contributors
> > familiar with various relevant areas of LLVM.
> >
> > Additionally, there are opportunities to refactor generic
> > infrastructure in LLVM to better support the needs of virtual ISAs,
> > including those in LLVM already and possibly more in the future.
> > Working in LLVM from the start would make collaboration with the rest
> > of the community easier.
>
> I agree, developing the backend in tree is the best path. Specifically, it
> is the best way for the community to monitor the development and ensure
> proper test coverage. Obviously, there are some number of files needed for
> a backend to be minimally functional, and I think that putting those
> together and submitting them for review as a new experimental backend is
> perfectly appropriate.
>

FWIW, I agree.

However, I also suggested this approach, so I'm probably biased. ;] I just
wanted to explicitly say that I think this is a great path forward and I'm
cautiously optimistic about the entire effort.


>
>  -Hal
>
> >
> > We look forward to your feedback and questions. Thanks!
> >
> >         - The WebAssembly Community Group
> >
> > [0] https://github.com/WebAssembly/design/blob/master/README.md
> > [1]
> > https://github.com/WebAssembly/design/blob/master/HighLevelGoals.md
> >
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> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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