Exploiting Vectorization in High Level Synthesis of Nested Irregular Loops

Synthesis of DoAll loops is a key aspect of High Level Synthesis since they allow to easily exploit the potential parallelism provided by programmable devices. This type of parallelism can be implemented in several ways: by duplicating the implementation of body loop, by exploiting loop pipelining or by applying vectorization. In this paper a methodology for the synthesis of nested irregular DoAll loops based on outer vectorization is proposed. The methodology transforms the intermediate representation of the DoAll loop to introduce vectorization and it can be easily integrated in existing state of the art High Level Synthesis flows since does not require any modification in the rest of the flow. Vectorization is not limited to perfectly nested countable loops: conditional constructs and loops with variable number of iterations are supported. Experimental results on parallel benchmarks show that the generated parallel accelerators have significant speed-up with limited penalties in terms of resource usage and frequency decrement.