ispc is a new compiler for “single program, multiple data” (SPMD) programs. Under the SPMD model, the programmer writes a program that mostly appears to be a regular serial program, though the execution model is actually that a number of program instances execute in parallel on the hardware. ispc compiles a C-based SPMD programming language to run on the SIMD units of CPUs; it frequently provides a 3x or more speedup on CPUs with 4-wide SSE units, without any of the difficulty of writing intrinsics code.
There are a few principles and goals behind the design of ispc:
- To build a small C-like language that delivers excellent performance to performance-oriented programmers who want to run SPMD programs on the CPU.
- To provide a thin abstraction layer between the programmer and the hardware—in particular, to have an execution and data model where the programmer can cleanly reason about the mapping of their source program to compiled assembly language and the underlying hardware.
- To make it possible to harness the computational power of SIMD vector units without the extremely low-programmer-productivity activity of directly writing intrinsics.
- To explore opportunities from close coupling between C/C++ application code and SPMD ispc code running on the same processor—to have lightweight function calls between the two languages and to share data directly via pointers without copying or reformatting.
ispc is an open source compiler with a BSD license. It uses the remarkable LLVM Compiler Infrastructure for back-end code generation and optimization and is hosted on github. It supports Windows, Mac, and Linux, with both x86 and x86-64 targets. It currently supports the SSE2 and SSE4 instruction sets, though support for AVX should be available soon.