Trace-directed program restructuring for AIX executables

This paper presents the design and implementation of trace- directed program restructuring (TDPR) for AIX® executable programs. TDPR is the process of reordering the instructions in an executable program, using an actual execution profile (or instruction address trace) for a selected workload, to improve utilization of the existing hardware architecture. Generally, the application of TDPR results in faster programs, programs that use less real memory, or both. Previous similar work [1–6] regarding profile-guided or feedback-directed program optimization has demonstrated significant improvements for various architectures. TDPR applies these concepts to AIX executable programs at a global level (i.e., independent of procedure or other structural boundaries) running on the POWER, POWER2™, and PowerPC 601™ machines and adds the methodology to preserve correctness and debuggability for reordered executables. Using the prototype tools developed for this effort on a selection of both user-level application prog rams and operating system (kernel) code, improvements in execution time of up to 73% and reduced instruction memory requirements of up to 61% were measured. The techniques used to restructure AIX executables are discussed, and the performance improvements and memory reductions measured for several application programs are presented.