Source-Level Debugging of Scalar Optimized Code
A. Adl-Tabatabai
and T. Gross, "Source-Level Debugging of Scalar
Optimized Code", Proc. ACM SIGPLAN Symp. on Programming Language
Design and Implementation, May, 1996, 33-43.
Abstract
Although compiler optimizations play a crucial role in the performance
of modern computer systems, debugger technology has lagged behind in
its support of optimizations. Yet debugging the unoptimized
translation is often impossible or futile, so handling of code
optimizations in the debugger is necessary. But compiler
optimizations make it difficult to provide source-level debugger
functionality: Global optimizations can cause the runtime value of a
variable to be inconsistent with the source-level value expected at a
breakpoint; such variables are called endangered variables. A
debugger must detect and warn the user of endangered variables
otherwise the user may draw incorrect conclusions about the program.
This paper presents a new algorithm for detecting variables that are
endangered due to global scalar optimizations. Our approach provides
more precise classifications of variables and is still simpler than
past approaches. We have implemented and evaluated our techniques in
the context of the cmcc optimizing C compiler. We describe the
compiler extensions necessary to perform the required bookkeeping of
compiler optimizations. We present measurements of the effect of
optimizations on a debugger's ability to present the expected values
of variables to the user.
Postscript
ali@cs.cmu.edu