[llvm-dev] [RFC] Add a new backend called LoongArch

[Renato Golin via llvm-dev]

Excellent! Thanks for the answers.

As for the patches, if those are the only 5 initial patches, to make the
arch work on its own initially, do you mind renaming them 1/5, 2/5 .. 5/5?

It's hard to know how many more patches are needed if you use 'n' and
reviewers keep wondering if whatever is missing will come in a later patch
or not.

If we ask for a split (on a large patch, for example), then just rename to
however many patches there are. For example, if 2/5 splits in 2, then it
becomes 2/6 and 3/6, and the rest accordingly.

Once we get through the initial phase, you don't need to continue numbering
the patches.

Thanks!

On Fri, 17 Dec 2021 at 07:23, Weining Lu <luweining at loongson.cn> wrote:

> Thanks for your comments. Renato
>
>
> Per your questions:
>
> 1. Loongson Binary Translation (LBT)  is targeting binary translation
> from other architectures(like X86, ARM) to LoongArch.
>
> 2. Right, currently the documents for binary translation and vector
> extension are TBD. But those will be available before we bringing these
> extensions to LLVM.
>
> 3. Hardware or emulator: AFAIK there are some PC based on 3A5000 can be
> bought at https://www.jd.com/ (a Chinese online shopping website. I'm not
> sure if there is an English version ).
>
>    Searching "3A5000" will show several products, like
> https://item.jd.com/100015866577.html and
> https://item.jd.com/100023656622.html
>
>    Beside this, qemu and CLFS are available at
> https://github.com/loongson/build-tools which are convenient to try on.
>
> 4. The 5 initial patches are
>
> https://reviews.llvm.org/D115857
>
> https://reviews.llvm.org/D115859
>
> https://reviews.llvm.org/D115860
>
> https://reviews.llvm.org/D115861
>
> https://reviews.llvm.org/D115862
>
> Please help to reivew them or recommend other reviewers. Any comments are
> appreciate.
>
>
> Thanks,
>
> Weining
>
>
> -----原始邮件-----
> *发件人:*"Renato Golin" <rengolin at gmail.com>
> *发送时间:*2021-12-17 04:06:45 (星期五)
> *收件人:* "陆伟宁" <luweining at loongson.cn>
> *抄送:* llvm-dev <llvm-dev at lists.llvm.org>, "余银" <yuyin-hf at loongson.cn>,
> "翟小娟" <zhaixiaojuan at loongson.cn>
> *主题:* Re: [llvm-dev] [RFC] Add a new backend called LoongArch
>
> Hi  Weining,
>
> Welcome to the LLVM community!
>
> I had a look at the documentation and your fork and the description you
> gave matches what the community expects of new targets, so thanks for
> making the effort to know what to do before proposing a new target!
>
> Some more comments below...
>
> On Thu, 16 Dec 2021 at 07:55, 陆伟宁 via llvm-dev <llvm-dev at lists.llvm.org>
> wrote:
>
>> 1. LoongArch intro
>> LoongArch is a RISC style ISA which is independently designed by Loongson
>> Technology in China. It is divided into two versions, the 32-bit version
>> (LA32)
>> and the 64-bit version (LA64). LA64 applications have application-level
>> backward binary compatibility with LA32 applications. LoongArch is
>> composed of
>> a basic part (Loongson Base) and an expanded part. The expansion part
>> includes
>> Loongson Binary Translation (LBT), Loongson VirtualiZation (LVZ),
>> Loongson SIMD
>> EXtension (LSX) and Loongson Advanced SIMD EXtension(LASX).
>
>
> That's an interesting target. It seems very sensible on its instruction
> encoding, data sizes and alignment, etc.
>
> I'm just curious about the binary translation unit. Is that to support
> LA32/LA64 interchangeably (like x86_64 and AArch64 do with their 32-bit
> counterparts), or is that for some other architecture (like MIPS or Arm)?
>
> 2. Conform to the policy
>> According to
>> https://llvm.org/docs/DeveloperPolicy.html#adding-a-new-target
>> a) Of couse it will be an experimental target at first.
>> b) I'd like to be the code owner of this target.
>> c) There is an active community behind the target:
>> https://github.com/loongson
>>    And we will provide builbot support.
>
>
> Sounds great!
>
> d) Documentations:
>>  - ISA:
>>
>> https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html
>>  - ABI:
>>
>> https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html
>>  - More docs can be found at:
>>    https://loongson.github.io/LoongArch-Documentation/README-EN.html
>
>
> Some documents there (binary translation, vector extension) are TBD.
>
> Given that the current llvm fork you have is only for basic support, I
> imagine you'll tackle that after the basic support is merged. Before
> bringing extensions, we'd need documents for those, too.
>
> The one thing left is to know if there are existing implementations of the
> hardware (as a product or a dev board) and/or if there are emulators freely
> available.
>
> This is important for people that want to test the back-end on your
> hardware (for example, while debugging unrelated changes that break on your
> target).
>
> 3. Status
>> We started to implement an out-of-tree LoongArch LLVM port since last year
>> based on llvm-8/11 and posted it to
>> https://github.com/loongson/llvm-project
>> last month. This port also adds supports to clang front-end and we
>> finally pass
>> 100% llvm-test-suite in O0/1/2/3 optimization levels.
>
>
> This is actually really nice!
>
> But in this port there
>> are a few issues we must handle to get it upstreamed.
>>  - The codebase is too old that means we may use some out-of-date
>> interfaces.
>
>
> Your fork is based on the tree as of Oct 2020, that's more than a year ago
> and in LLVM's timeframes, an eternity.
>
> That usually means you'll have to re-write a good portion of your existing
> code, but I'm assuming you already knew that and is happy to proceed.
>
>  - The test coverage is not broad enough.
>
>
> Given that you pass the test-suite, I'm assuming you can generate a good
> portion of the use cases.
>
> But it is important to also have extensive LIT tests (IR-to-IR, MIR, DAG,
> SRC-to-IR, etc) to avoid needing to run the test-suite for basic support
> testing.
>
>  - Coding standard is not met.
>
>
> I'm sure you know this is a deal breaker. But since you're going to have
> to re-write good part of the code, I'm also assuming you're happy making
> your new code meet the standards. :)
>
> The current status is that we have completed a series of 5 patches adding
>> triple, ELF machine, basic interger instructions and registers
>> definition. We
>> will submit them for review later. Any comments are welcome and please do
>> let
>> me know if you'd like to be added as a reviewer to future patches.
>
>
> This sounds like a good start. Let's get to lowering and parsing a
> function with a few arguments, instructions and a return value, and their
> respective tests.
>
> Name those patches [X/N] with X being 1..N and N being the total number of
> patches in the first series. They need to be reviewed all at the same time
> and only when all are approved we can merge them all together.
>
> This is important to make sure new targets start at the right place. From
> them on, you won't need to number the patches, and can incrementally
> develop your target to reach maturity.
>
> So, overall, I think this looks promising. Your target seems to meet the
> criteria we set for new targets, so looking forward to seeing the initial
> patches!
>
> Thanks!
> Renato
>
>
>
>
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