[llvm-dev] [RFC] Promoting the RISC-V backend from 'experimental' to 'official' for 9.0

[Finkel, Hal J. via llvm-dev]

On 7/8/19 5:19 PM, Alex Bradbury via llvm-dev wrote:
> The 9.0 release is currently scheduled to branch in 10 days time, on
> the 18th of July, with a final release expected on 28th August. I
> would like to propose promoting the RISC-V backend from its current
> "experimental" status to "official" prior to this branch. This means
> that the RISC-V backend will be built by default and support included
> in standard binary distributions of LLVM/Clang.
>
> # Status
>
> RISC-V is a modular ISA with 32- and 64-bit variants, as well as a range of
> options specified in "ISA naming strings". The RISC-V backend supports
> both variants and all standard extensions. RV32IMAFDC, RV64IMAFDC, and
> the ilp32, ilp32f, ilp32d, lp64, lp64f, lp64d ABIs (the clang
> hard-float ABI patch will land imminently
> <https://reviews.llvm.org/D60456>).
>
> We have a fairly comprehensive out set of in-tree unit tests, multiple
> groups have indicated they are using Clang/LLVM for their RISC-V
> embedded firmware builds and more recently we have been pushing
> forwards on issues related to building Linux/FreeBSD applications. The
> GCC torture suite has a 100% pass rate, we're seeing a 98% pass rate
> on the LLVM test-suite (failures are almost all related to C++
> exception handling, which we hope to resolve soon), and we've been
> able to get over 90% of buildroot's over 20000 packages to build for
> RISC-V using clang, where most failures are due to build system issues
> or GCCisms. We can compile and run meaningful programs (e.g. build a
> rootfs with nginx, serve HTTP requests).


Does Clang/LLVM self host?


>
> Additionally, I understand that LLD support is now roughly feature-complete
> with the exception of support for linker relaxation. Fangrui Song has been
> most active on RISC-V LLD recently.
>
> There is initial Rust support for bare metal rv32 and rv64, with support for
> hard float Linux targets due to start soon.
>
> I believe that we are ready to flip the switch towards an 'official' target.
> At lowRISC, we're ready to address any issues that arise, and as noted below
> we're delighted that there's a growing community of contributors around this
> backend who are equally invested in its success.
>
> ## Thanks
>
> I started work on the RISC-V LLVM backend around the end of 2016
> through lowRISC, a not-for-profit open source hardware/software
> engineering company I co-founded. I'd like to thank everyone who gave
> encouragement, helped with funding in order to support this work, or
> submitted reviews or patches. As well as growing the toolchain team at
> lowRISC (Luís Marques, Sam Elliott, and myself), we've been able to
> help grow a community of contributors around this work. There are far
> too many names to mention, but engineers from organisations such as
> Qualcomm, AndesTech, Embecosm, Google, and the University of Cambridge
> have all made notable contributions.
>
> ## End
>
> Although becoming an official backend would be a huge milestone, of course it's
> far from the end of the road. We'll be continuing to work on code size and
> generated code performance improvements, better testing, working with language
> communities like Rust/Swift/Julia/..., support for additional LLVM features
> and RISC-V instruction set extensions, etc.
>
> Any questions / concerns / feedback?


This sounds like great progress.

Is there a buildbot?

  -Hal


>
> --
> Alex Bradbury,
> CTO and Co-Founder, lowRISC CIC
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory