| 摘要 |
A method and apparatus for efficient propagation of attribute bits in an instruction decoding pipeline. Attribute bits associated with instructions are manipulated in a like manner to the instructions in an instruction decode pipeline. The pipeline has three pipe stages. Some of the attribute bits are generated in the first pipe stage but not used until the third pipe stage. A prefetch buffer stores prefetched instruction bytes. Attribute bits for each prefetched instruction byte are generated and stored in an attribute buffer in locations corresponding to the instruction bytes stored in the prefetch buffer. A code rotator selects two sequential instructions from the prefetch buffer and stores them in an instruction FIFO for later decoding and execution in the pipeline. In like manner and in parallel, an attribute rotator selects two sets of attribute bits corresponding to the selected instructions and stores them in the instruction FIFO. The attribute bits control certain operations in the decoding and execution of the selected instructions.
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