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4.2 Efficiency

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The following factors greatly reduce the overhead expense involved in a PA-RISC procedure call:

  1. Allocation of the stack frame and saving of one callee-saves register can be accomplished in a total of one cycle. (The same is also true for the deallocation of the frame and restoration of one register.)

  2. Even when not optimizing, the delay slot (i.e. the instruction slot following a Branch instruction) is used for operations such as loading register values and passing parameters.

  3. Most of the steps involved in a call are optional if they are unnecessary in a particular situation. (For example, saving and restoring RP, saving and restoring callee-saves registers, allocating stack storage space, etc.)



4.1 Control Flow of a Standard Procedure Call

4.3 The Code Involved in a Simple Local Call