Android Renderscript

Renderscript is Android's advanced 3D graphics rendering and compute API. It provides a portable C99-based language with extensions to facilitate common use cases for enhancing graphics and thread level parallelism. The Renderscript compiler frontend is based on Clang/LLVM. It emits a portable bitcode format for the actual compiled script code, as well as reflects a Java interface for developers to control the execution of the compiled bitcode. Executable machine code is then generated from this bitcode by an LLVM backend on the device. Renderscript is thus able to provide a mechanism by which Android developers can improve performance of their applications while retaining portability. This talk focuses on the design and implementation of Renderscript using Clang/LLVM. Renderscript leverages Clang's AST to provide a Java reflection of globally visible symbols in the compilation unit. This includes both global variables as well as invocable parameterized functions. We also transform the Clang-based AST before emitting bitcode to provide support for reference-counted types that span the Renderscript/Java memory domains. Renderscript uses bitcode as a portable code format so that we can leverage other hardware architectures in addition to the CPU in the future (GPU, DSP). Interesting facts: - Difference in Clang source: 6 lines (all upstreamable with a bit of configuration logic) - Difference in LLVM source: ~300 lines (possibly worth upstreaming, but some fixes for legacy JIT mode are no longer relevant to TOT) - The frontend compiler is layered completely on top of Clang, so everything we use is sub-classed and/or recombined for our purposes in the llvm-rs-cc compiler driver. - The backend compiler is stripped down to fit on a tablet/smartphone stack.