The LLVM open source project will contain a subproject named parallel-libs which will host the development of libraries which are aimed at enabling parallelism in code and which are also closely tied to compiler technology. Examples of libraries suitable for hosting within the parallel-libs subproject are runtime libraries and parallel math libraries. The initial candidates for inclusion in this subproject are StreamExecutor and libomptarget which would live in the streamexecutor and libomptarget subdirectories of parallel-libs, respectively.
The parallel-libs project will host a collection of libraries where each library may be dependent on other libraries from the project or may be completely independent of any other libraries in the project. The rationale for hosting independent libraries within the same subproject is that all libraries in the project are providing related functionality that lives at the intersection of parallelism and compiler technology. It is expected that some libraries which initially began as independent will develop dependencies over time either between existing libraries or by extracting common code that can be used by each. One of the purposes of this subproject is to provide a working space where such refactoring and code sharing can take place.
Libraries in the parallel-libs subproject may also depend on the LLVM core libraries. This will be useful for avoiding duplication of code within the LLVM project for common utilities such as those found in the LLVM support library.
Libraries included in the parallel-libs subproject must strive to achieve the following requirements:
- Adhere to the LLVM coding standards.
- Use the LLVM build and test infrastructure.
- Be released under LLVM's license.
Libraries in parallel-libs will match the LLVM coding standards. For existing projects being checked into the subproject as-is, an exception will be made during the initial check-in, with the understanding that the code will be promptly updated to follow the standards. Therefore, a three month grace period will be allowed for new libraries to meet the LLVM coding standards.
Additional exceptions to strict adherence to the LLVM coding standards may be allowed in certain other cases, but the reasons for such exceptions must be discussed and documented on a case-by-case basis.
Using the LLVM build and test infrastructure currently means using cmake for building, lit for testing, and buildbot for automating build and testing. This project will follow the main LLVM project conventions here and track them as they evolve.
Each subproject library will be able to build separately without a single, unified cmake file, but each subproject libraries will also be integrated into the LLVM build so they can be built directly from the top level of the LLVM cmake infrastructure.
For simplicity, the parallel-libs project will use the normal LLVM license. While some runtime libraries use a dual license scheme in LLVM, we anticipate the project removing the need for this eventually and in the interim follow the simpler but still permissive license. Among other things, this makes it straightforward for these libraries to re-use core LLVM libraries where appropriate.
Two mailing lists will be set up for the project:
- parallel_libs-dev@lists.llvm.org for discussions among project developers, and
- parallel_libs-commits@lists.llvm.org for patches and commits to the project.
Each subproject library will manage its own components in Bugzilla. So, for example, there can be several Bugzilla components for different parts of StreamExecutor, etc.