Runtime Optimization

Runtime optimization has become an important technique for the implementation of many programming languages. The move from ahead-of-time compilation to runtime optimization lets the language runtime and its compilers capitalize on facts that are not known until runtime. If these facts enable specialization of the code, such as folding an invariant value, avoiding type conversion code, or replacing a virtual function call with a direct call, then the profit from use of runtime information can be substantial. This chapter explores the major issues that arise in the design and implementation of a runtime optimizer. It describes the workings of a hot-trace optimizer and a method-level optimizer; both are inspired by successful real systems. The chapter lays out some of the tradeoffs that arise in the design and implementation of these systems.