With-Loop Scalarization - Merging Nested Array Operations

Abstract. Construction of complex array operations by composition of more basic ones allows for abstract and concise specifications of algorithms. Unfortunately, näıve compilation of such specifications leads to creation of many temporary arrays at runtime and, consequently, to poor performance characteristics. This paper elaborates on a new compiler optimization, named withloop-scalarization, which aims at eliminating temporary arrays in the context of nested array operations. It is based on with-loops, a versatile array comprehension construct used by the functional array language SaC both for specification as well as for internal representation of array operations. The impact of with-loop-scalarization on the runtime performance of compiled SaC code is demonstrated by several experiments involving support for arithmetic on arrays of complex numbers and the application kernel FT from the NAS benchmark suite.