Pipestage Creation

Given an intermediate process of the form specified in the previous paragraph, the following occurs during Pipestage Creation  

The final RECV / SEND pair of operators in process Vj are removed. 

The set of values A (that was sent back to the previous stage Vi, but that was not received from the next stage Vk) is sent to the next stage Vk, and from there to all successive stages until the final stage is reached, where it is sent directly back to the first stage. 

It is assumed that the pipestages will execute in lockstep, and all data transfers between the pipestages will occur at the same time. This assumption may be enforced either through control step scheduling, through added hardware or microcode, or by some other method. 

The preceding portion of Section 3.6 described a transformation for creating pipestages. Before this transformation can be applied. Process 

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SELECT Duplication, SELECT-to-SELECT Transfer, and SELECT Output Closure are often used together with the Process Creation and Pipestage Creation transformations described later to form pipestages. 

Figure 8-15. Call Graphs After Pipestage Creation...

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