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Summary: For AMDGPU, we have been using the operating system component of the triple for specifying the low-level runtime that is being used. The rationale for this is that the host operating system (e.g. Linux) is irrelevant for GPU code, since its execution enviroment will be mostly controled by the low-level runtime being used to execute the code. In most cases, higher level languages have their own runtime which is implemented on top of the low-level runtime. The kernel ABIs of each language mostly depend on the low-level runtime, but there may be some slight differences between languages. OpenCL for example, may append additional arguments to the kernel in order to pass values like global offsets or buffers for printf. OpenMP, HCC, or other languages may want to add their own values which differ from OpenCL. The reason for adding a new opencl environment type is to make it possible for the backend to distinguish between the ABIs of the higher-level languages and handle them correctly. It seems cleaner to use the enviroment component for this rather than creating a new OS type for every combination of low-level runtime / high-level language. Reviewers: Anastasia, chandlerc Subscribers: whchung, pekka.jaaskelainen, wdng, yaxunl, llvm-commits Differential Revision: https://reviews.llvm.org/D24735 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282218 91177308-0d34-0410-b5e6-96231b3b80d8
Design Of lib/System
====================
The software in this directory is designed to completely shield LLVM from any
and all operating system specific functionality. It is not intended to be a
complete operating system wrapper (such as ACE), but only to provide the
functionality necessary to support LLVM.
The software located here, of necessity, has very specific and stringent design
rules. Violation of these rules means that cracks in the shield could form and
the primary goal of the library is defeated. By consistently using this library,
LLVM becomes more easily ported to new platforms since the only thing requiring
porting is this library.
Complete documentation for the library can be found in the file:
llvm/docs/SystemLibrary.html
or at this URL:
http://llvm.org/docs/SystemLibrary.html
While we recommend that you read the more detailed documentation, for the
impatient, here's a high level summary of the library's requirements.
1. No system header files are to be exposed through the interface.
2. Std C++ and Std C header files are okay to be exposed through the interface.
3. No exposed system-specific functions.
4. No exposed system-specific data.
5. Data in lib/System classes must use only simple C++ intrinsic types.
6. Errors are handled by returning "true" and setting an optional std::string
7. Library must not throw any exceptions, period.
8. Interface functions must not have throw() specifications.
9. No duplicate function impementations are permitted within an operating
system class.
To accomplish these requirements, the library has numerous design criteria that
must be satisfied. Here's a high level summary of the library's design criteria:
1. No unused functionality (only what LLVM needs)
2. High-Level Interfaces
3. Use Opaque Classes
4. Common Implementations
5. Multiple Implementations
6. Minimize Memory Allocation
7. No Virtual Methods