Some JIT compilers are even capable of de-optimizing code.
Z MACHINE INTERPRETER CHROMEBOOK CODE
Some compilers may gather information while the program is running and recompile code several times as new information becomes available that allows them to better optimize it. Some compile whole modules or classes, some whole methods, some only smaller blocks. Some JIT compilers compile code only once. Some JIT compilers wait until the code needs to be executed. Within the family of JIT compilers, there are still many differences as to when exactly they compile, how often, and at what granularity.įor example, some JIT compilers compile code as soon as it is loaded for the first time. The idea of an AOT interpreter that runs a program before it runs or a JIT interpreter that runs a program while it is running is nonsensical. Note that this distinction doesn't make sense for interpreters: an interpreter runs the program. (So, for example, a JIT compiler which compiles JavaScript to x86 machine code doesn't make sense without an x86 CPU it compiles the program while it is running, but without the x86 CPU the program wouldn't be running.) Note that this requires that a JIT compiler from language X to language Y must somehow work together with an interpreter for language Y, otherwise there wouldn't be any way to run the program. a JIT compiler compiles the program as it is running, an AOT compiler compiles the program before it is running. The terms Ahead-of-Time (AOT) and Just-in-Time (JIT) refer to when compilation takes place: the "time" referred to in those terms is "runtime", i.e. (Note that X and Y may be the same language.) that interpreting p′ with an interpreter for Y will yield the same results and have the same effects as interpreting p with an interpreter for X. CPUs are usually interpreters for their respective instructions sets, although modern high-performance workstation CPUs are actually more complex than that they may actually have an underlying proprietary private instruction set and either translate (compile) or interpret the externally visible public instruction set.Ī compiler from X to Y is a program (or a machine, or just some kind of mechanism in general) that translates any program p from some language X into a semantically equivalent program p′ in some language Y in such a way that the semantics of the program are preserved, i.e. An interpreter for language X is a program (or a machine, or just some kind of mechanism in general) that executes any program p written in language X such that it performs the effects and evaluates the results as prescribed by the specification of X.
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