History of Compiler Construction - Optimizing Compilers - Capex COBOL Optimizer

Capex COBOL Optimizer

Capex Corporation developed the "COBOL Optimizer" in the mid 1970s for COBOL. This type of optimizer depended, in this case, upon knowledge of 'weaknesses' in the standard IBM COBOL compiler, and actually replaced (or patched) sections of the object code with more efficient code. The replacement code might replace a linear table lookup with a binary search for example or sometimes simply replace a relatively 'slow' instruction with a known faster one that was otherwise functionally equivalent within its context. This technique is now known as "Strength reduction". For example on the IBM/360 hardware the CLI instruction was, depending on the particular model, between twice and 5 times as fast as a CLC instruction for single byte comparisons.

Modern compilers typically provide optimization options, so programmers can choose whether or not to execute an optimization pass.