Abstract: Systems and methods for just-in-time compilation are disclosed. The systems and methods can be used to generate composite blocks, reducing program execution time. The systems and methods can include generating single-trace blocks during program execution. Upon satisfaction of a trigger criterion, single-trace blocks can be selected for compilation into a composite block. The trigger criterion can be a number of executions of a trigger block. Selecting the single-trace blocks can include identifying blocks reachable from the trigger block, selecting a subset of the reachable blocks, and selecting an entry point for the composite block. The composite block can be generated from the single-trace blocks and incorporated into the program control flow, such that the composite block is executed in place of the selected single-trace blocks.