high performance computing on graphics processing units: hgpu.org

Programming languages such as C for CUDA, OpenCL or ISPC have contributed to increase the programmability of SIMD accelerators and graphics processing units. However, these languages still lack the flexibility offered by lowlevel SIMD programming on explicit vectors. To close this expressiveness gap while preserving performance, this paper introduces the notion of Call Re-Vectorization (CREV). CREV allows changing the dimension of vectorization during the execution of a kernel, exposing it as a nested parallel kernel call. CREV affords programmability close to dynamic parallelism, a feature that allows the invocation of kernels from inside kernels, but at much lower cost. In this paper, we present a formal semantics of CREV, and an implementation of it on the ISPC compiler. We have used CREV to implement some classic algorithms, including string matching, depth first search and Bellman-Ford, with minimum effort. These algorithms, once compiled by ISPC to Intel-based vector instructions, are as fast as state-of-the-art implementations, yet much simpler. Thus, CREV gives developers the elegance of dynamic programming, and the performance of explicit SIMD programming.