Vtbody Inline Expansion

Vtbody Inline Expansion replaces a CALL operator with the contents of the called vtbody. In the Workbench, CALLs are not expanded if the vtbody being CALLed has more than one LEAVE operator, or if it RESTARTS, RESUMES, or TERMINATES itself these restrictions avoid GOTO-style jumps to the interior of a vtbody (which are not allowed in the VT). 

Similar to dead code elimination in optimizing compilers. Dead Vtbody Elimination removes a vtbody that is not called by other vtbodies. An automated version of the transformation is also available that removes all vtbodies not called by others. For example, applying Dead Vtbody Elimination to the VT on the right side of Figure 3-2 would remove vtbody V2 B, which is no longer referenced by other vtbodies. This transformation is typically applied after Vtbody Inline Expansion. 

Vtbody Formation encapsulates a specified set of operators into a new vtbody, which is then CALLed from the original vtbody. This is the inverse of Vtbody Inline Expansion. An example of Vtbody Formation is shown in Figure 3-3, where an increment statement and its contents are encapsulated into a separate vtbody. 

First, unnecessary microsubroutine calls can be eliminated by using Vtbody Inline Expansion to recursively expand all vtbodies inline, producing a single large vtbody if possible. Once this expansion has been performed. Dead Vtbody Elimination can be used to remove the vtbodies that are no longer referenced. 

---