Quantifying and evaluating the space overhead for alternative C++ memory layouts

  • Authors:

  • Peter F. Sweeney;Michael Burke

  • Affiliations:

  • IBM, Thomas J. Watson Research Center, P.O. Box 704, Yorktown Heights, NY;IBM, Thomas J. Watson Research Center, P.O. Box 704, Yorktown Heights, NY

  • Venue:
  • Software—Practice & Experience
  • Year:
  • 2003

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Abstract

This paper develops a formalism that precisely characterizes when class tables are required for C++ memory layouts. A memory layout is a particular choice of data structures for implementing run-time support for object-oriented languages. We use this formalism to quantify and evaluate, on a set of benchmarks, the space overhead for a set of C++ memory layouts. In particular, this paper studies the space overhead due to three language features: virtual dispatch, virtual inheritance, and dynamic typing. To date, there has been no scientific quantification or evaluation of C++ memory layouts. Our approach can help C++ implementors. This work has already influenced the memory layout design choices in IBM's Visual Age C++ V5 compiler.Applying our approach to a set of five benchmarks, we demonstrate that the impact of object-oriented space overhead can vary dramatically between applications (ranging from 0.42% to 99.79% for our benchmarks). In particular, applications whose object space is dominated by instances of classes that heavily use object-oriented language features will be significantly impacted by the choice of a memory layout.