A dynamic translator emulates an instruction set architecture by translating source instructions to native code during execution. On statically-scheduled hardware, higher performance can potentially be achieved by reordering the translated instructions; however, this is a challenging transformation if the source architecture supports precise exception semantics, and the user-level program is allowed to register exception handlers. This paper presents a software technique which allows a translator to achieve the out-of-order execution of user-level programs, while preserving all sequential semantics. The design combines a translator, an interpreter, and a set of operating system services. Using the proposed techniques, a dynamic translator can optimistically reorder instructions and speculate them across branch boundaries. If a mispeculated operation causes an exception, the recovery algorithm reverts the application state to a safe point, then retranslates the faulty code without reordering to disable further exceptions.
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