This page has my notes from initial study for Android RenderScript.

RenderScript is Android 3D graphics rendering and intensive computation using heterogeneous computing.
1. Portability: A general purpose compute API across different system computing hardware
2. High Performance
3. Developer Friendly: A compute API similar to CUDA, OpenCL or GLSL, and a familiar language with C99

There are three major components in RenderScript
1. Offline compiler (llvm-rs-cc): Convert script files into portable bitcode and reflected Java layer
2. Online JIT compiler (libbcc): Translate portable bitcode to appropriate machine code (CPU/GPU/DSP/…)
3. Runtime library support (libRS): Manage scripts from Dalvik layer and also provide basic support libraries (math functions, etc.)
A good introduciton of Android RenderScript on LLVM is given by Shih-Wei Liao, and a good comparsion and analysis of different android programming model is given by Kandroid S/W Fundamentals Study Group at 12th Kandroid Conference, 2013.

Clang is offline frontend compiler to create LLVM bitcode and reflected Java layer. The portable bitcode supplied as a resource within .apk container and is compiled before use one the device. Offline compiler, llvm-rs-cc, performs machine-independent optimizations on host before emitting portable bitcode so that the online JIT on android devices can be light-weight.

Online JIT compiler, libbcc, performs target-specific optimizations and code generation and links dynamically against vendor-specific runtime library funcitons (lib*.bc). An example: RenderScript’s runtime (libclcore.bc) comes with vector operations. Xoom’s libclcore will have different CPU/GPU support (VFP3-16) than Nexus S’s (NEON).