Increasing software-pipelined loops in the itanium-like architecture

The Itanium architecture (IPF) contains features such as register rotation to support efficient software pipelining. One of the drawbacks of software pipelining is its high register requirement, which may lead to failure when registers provided by architecture are insufficient. This paper evaluates the register requirements of software-pipelined loops in Itanium architecture and presents two new methods, which try to reduce static general register requirements in software pipelined loops by either reducing instructions in the loop body or allocating unused rotating registers for variants using static registers. We have implemented our methods in the Open Research Compiler (ORC) targeted for Itanium processors, and experiments show that number of software-pipelined loops in NAS Benchmarks increased. For some benchmarks, the performance is improved by more than 18%.