The LANCE three address code IR is defined as a subset of ANSI C. The IR format is common to all LANCE optimization tools which work in a "plug-and-play" fashion. By inheriting the IR semantics from ANSI C, the IR gets easy to understand and thus enables extensions of the system with custom optimizations. Since the IR can be compiled by any ANSI C compiler, validation of new IR optimization tools can be performed on a host machine without the need for a target specific backend or instruction set simulator.