Register pipelining: An integrated approach to register allocation for scalar and subscripted variables

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Abstract

Conventional compilers typically ignore the potential benefits of keeping array elements in registers for reuse, due in part to the fact that standard data flow analysis techniques used in register allocation are not expressive enough to distinguish among individual array elements. This paper introduces the concept of register pipelining as an integrated approach to register allocation for both scalar and subscripted variables. A register pipeline is a set of registers that is allocated to the live ranges of array elements inside a loop. By preserving the computed array elements in the pipeline stages, reuse is enabled across loop iterations. We present an efficient data flow algorithm that extends the construction of live ranges to array elements. To enable a fair competition among the live ranges of subscripted and scalar variables for the available registers, we developed an integrated version of the standard graph coloring algorithm for register allocation.