陆伟宁 via llvm-dev
2021-Dec-16 07:55 UTC
[llvm-dev] [RFC] Add a new backend called LoongArch
Hi all, We are proposing the integration of a new backend targeting the LoongArch ISA. 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). Currently the LA464 processor core supports LoongArch ISA and the Loongson 3A5000 processor integrates 4 64-bit LA464 cores. LA464 is a four-issue 64-bit high-performance processor core. It can be used as a single core for high-end embedded and desktop applications, or as a basic processor core to form an on-chip multi-core system for server and high-performance machine applications. 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. 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 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. 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 - The codebase is too old that means we may use some out-of-date interfaces. - The test coverage is not broad enough. - Coding standard is not met. So we decide to refactor this port base on llvm trunk and integrate to upstream incrementally. This approach of small, incremental patches is somewhat similar to what has been or is being done with many other backends like RISC-V, CSKY and VE. 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. A rough development roadmap: - MC layer - CodeGen for Loongson Base - CodeGen for ISA extensions, including LSX and LASX - Support clang - Support other sub-projects Best regards, Weining Lu ------------------------------------------------------------------------------- Loongson Technology Corporation Limited Building No.2, Loongson Industrial Park, Zhongguancun Environmental Protection Park, Haidian District, Beijing -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20211216/692c33c5/attachment.html>
Renato Golin via llvm-dev
2021-Dec-16 20:06 UTC
[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.htmlSome 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20211216/9f82ba5e/attachment.html>