Improved Optimization of FORTRAN Object Programs

For many years the FORTRAN H Extended compiler has produced highly optimized object programs for IBM System/360 and System/370 computers. A study of the object programs revealed, however, that important additional optimizations were possible, and the compiler has been enhanced accordingly. First, the range of cases handled by the optimization techniques already present in the compiler has been extended. For example, more duplicate computations are eliminated, and more invariant computations are moved from inner to outer loops. Second, several new optimizations have been added, with subscript computation and register allocation receiving particular attention. Third, certain optimization restrictions have been removed. This paper describes these improvements and reports their effects.