C++ Expression Templates Performance Issues in Scientific Computing

Ever-increasing size and complexity of software applications and libraries in parallel scientific computing is making implementation in the programming languages traditional for this field—FORTRAN 77 and C—impractical. The major impediment to the progression to a higher-level language such as C++ is attaining FORTRAN 77 or C performance, which is considered absolutely necessary by many practitioners. The use of template metaprogramming in C++, in the form of so-called expression templates to generate custom C++ code, holds great promise for getting C performance from C++ in the context of operations on array-like objects. Several sophisticated expression template implementations of parallel array-class libraries exist, and in certain circumstances their promise of performance is realized. Unfortunately this is not uniformly the case; this paper explores the major reasons for this. A more complete version of this paper may be obtained from http://www.c3.lanl.gov/ ̃kei/ipps98.html.