Detection and recovery of endangered variables caused by instruction scheduling

Abstract

Instruction scheduling re-orders and interleaves instruction sequences from different source statements. This impacts the task of a symbolic debugger, which attempts to present the user a picture of program execution that matches the source program. At a breakpoint B , if the value in the run-time location of a variable V may not correspond to the value the user expects V to have, then this variable is endangered at B . This paper describes an approach to detecting and recovering endangered variables caused by instruction scheduling. We measure the effects of instruction scheduling on a symbolic debugger's ability to recover source values at a breakpoint. This paper reports measurements for three C programs from the SPEC suite and a collection of programs from the Numerical Recipes, which have been compiled with a variant of a commercial C compiler.