Debugging Optimized Code: Concepts and Implementation on DIGITAL Alpha Systems

Effective user debugging of optimized code has been a topic of theoretical and practical interest in the software development community for almost two decades, yet today the state of the art is still highly uneven. We present a brief survey of the literature and current practice that leads to the identification of three aspects of debugging optimized code that seem to be critical as well as tractable without extraordinary efforts. These aspects are (1) split lifetime support for variables whose allocation varies within a program combined with definition point reporting for currency determination, (2) stepping and setting breakpoints based on a semantic event characterization of program behavior, and (3) treatment of inlined routine calls in a manner that makes inlining largely transparent. We describe the realization of these capabilities as part of Compaq’s GEM back-end compiler technology and the debugging component of the OpenVMS Alpha operating system.