length指令确定字符串的长度并将其加载到一个整数寄存器中。
The length instruction determines the length of the string and loads it into an integer register.
为了生成主机处理器的正确的指令集，JIT编译器需要明确地确定底层的处理器的体系结构类型。
In order to generate the exact set of the host processor's instructions, the JIT compiler needs to precisely determine the architecture type of the underlying processor.
即使正确地确定了处理器的类型，JIT可能也不具备为未得到支持的处理器生成PPC指令子集的条件。
Even if the processor type is determined correctly, the JIT might not have provisions for producing a subset of PPC instructions for a non-supported processor.
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