[llvm-dev] RISC-V LLVM status update

[Tobias Grosser via llvm-dev]

On Mon, Aug 21, 2017, at 12:06, Alex Bradbury via llvm-dev wrote:
> As you will have seen from previous postings, I've been working on
> upstream
> LLVM support for the RISC-V instruction set architecture. The initial RFC
> <http://lists.llvm.org/pipermail/llvm-dev/2016-August/103748.html>
> provides a good overview of my approach. Thanks to funding from a third
> party,
> I've recently been able to return to this effort as my main focus. Now
> feels
> like a good time to give an update on where the RISCV backend is at, and
> how
> you can help.

Hey Alex,

thanks for the status update and congratulations to all your good work.
I am really looking forward to follow the upstreaming process over the
last weeks.

Best,
Tobias

> 
> ## Current status
> * A full, regularly rebased patchset can be found here
> <https://github.com/lowRISC/riscv-llvm>.
> * 16 of these patches have been put up for review so far. 7 have been
> committed, and 8 are awaiting review.
> * The vast majority of the GCC torture suite compiles and runs at O0,
> targeting RV32I. 1315 out of 1352 compile and run (32 compile-time
> failures, 5
> run-time failures).
> * I intend to keep <http://www.lowrisc.org/llvm/status> updated with
> status,
> test results etc.
> 
> ## Next steps and getting involved
> The plan has always been to work from the MC-layer upwards towards
> reliable
> RV32I codegen. This then provides a stable 'core' of the backend where
> it's
> easy for further development work to be parallelised, and for others to
> make
> contributions. I think we're now at that point.
> 
> I would really like to avoid setting up a new 'downstream', and to use
> this
> opportunity to pull in new people to upstream LLVM development.  However
> collaboration is made rather difficult for now due to the large gap
> between
> the patches that have been reviewed and committed upstream vs the
> complete
> patchset. If you would like to help, reviewing the remaining patches
> <https://reviews.llvm.org/differential/?authors=asb&order=updated> is an
> incredibly valuable way to do so. If you would like to be listed as a
> reviewer
> for future patches, just let me know (and feel free to add yourself for
> existing patches). I'll be doing some refactoring of RISCVInstrInfo.td as
> discussed here
> <http://lists.llvm.org/pipermail/llvm-dev/2017-August/116635.html>, but
> this
> is a straight-forward non-functional change. Other than that, there are
> no
> planned changes to the patches currently up for review.
> 
> My current plans look like the below, though of course will accelerate
> significantly with more contributors:
> * Next 2-3 weeks: resolve remaining torture suite issues, ABI compliance
> testing, documentation on MC layer backend implementation
> * End of Oct: Clang toolchain driver, initial MAFD MC layer + codegen +
> calling conventions, initial benchmarking vs RISC-V GCC and generated
> code
> quality improvements
> * End of Dec: finalise MAFD support, improve MAFD compliance testing and
> larger-scale codegen testing, further expanded backend docs, generated
> code
> quality improvements
> 
> I've mapped out a number of TODO items here
> <https://github.com/lowRISC/riscv-llvm/issues>, which I hope can help to
> co-ordinate efforts. Where possible, this indicates the current preferred
> approach (e.g. we plan to provide RV64 support building upon Krzysztof's
> variable-sized register class work). I've submitted a RISC-V BoF session
> proposal for the upcoming LLVM Dev Meeting. If accepted, this should
> provide a
> great opportunity to further discuss and co-ordinate work between the
> multiple
> parties who have expressed an interest.
> 
> ## Credits and support
> Thank you to everyone who has contributed review comments, suggestions,
> or
> code to this patchset and related support patches: Chandler Carruth,
> Chih-Mao
> Chen, David Chisnall, Simon Cook, David Craven, Hal Finkel, James Y
> Knight,
> David Majnemer, Ed Maste, Krzysztof Parzyszek, Jordy Portman, Philip
> Reames,
> Tim Northover, Eugene Zalenko, Florian Zeitz. Apologies to anybody who
> I've
> missed.
> 
> This work has been performed through lowRISC CIC
> <http://www.lowrisc.org>, a
> not-for-profit company. If your company would like to see my work on
> RISC-V
> LLVM to be sustained or to accelerate, contributing sponsorship and/or
> development time is the best way to do that. Please contact
> asb at lowrisc.org if
> you would like to discuss sponsorship, or have questions about code
> contributions that you can't discuss on-list.
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