We describe an approach to automatic parallelisation of programs written in Sieve C++ (Codeplay’s C++ extension), using the Sieve compiler and runtime system. In Sieve C++, the programmer encloses a performance-critical region of code in a sieve block, thereby instructing the compiler to delay side-effects until the end of the block. The Sieve system partitions code inside a sieve block into independent fragments and speculatively distributes them among multiple cores. We present implementation details and experimental results for the Sieve system on the Cell BE processor.