Interprocedural dataflow analysis in an executable optimizer

Interprocedural dataflow information enables link-time and post-link-time optimizers to perform analyses and code transformations that are not possible in a traditional compiler. This paper describes the interprocedural dataflow analysis techniques used by Spike, a post-linktime optimizer for Alpha/NT executables. Spike uses dataflow analysis to summarize the register definitions, uses, and kills that occur external to each routine, allowing Spike to perform a variety of optimizations that require interprocedural dataflow information. Because Spike is designed to optimize large PC applications, the time required to perform interprocedural dataflow analysis could potentially be unacceptably long, limiting Spike's effectiveness and applicability. To decrease dataflow analysis time, Spike uses a compact representation of a program's intraprocedural and interprocedural control flow that efficiently summarizes the register definitions and uses that occur in the program. Experimental results are presented for the SPEC95 integer benchmarks and eight large PC applications. The results show that the compact representation allows Spike to compute interprocedural dataflow information in less than 2 seconds for each of the SPEC95 integer benchmarks. Even for the largest PC application containing over 1.7 million instructions in 340 thousand basic blocks, interprocedural dataflow analysis requires just 12 seconds.