Simple Procedure Call and Return

• parameter transmission
• storage allocation/initialization
• transfer control

f(x) = x + y + f(z)

temporaries needed to hold results

Transfer Control

• Exit:
  • return address retrieved and stored
  • subroutine data freed
  • branch to return address
• Entry:
  • save return address
  • save data area

Simulating Recursion

• Entry:
  • declare stack
  • label first executable statement L1
• Recursive Calls:
  • store all parameters and local variables in stack
  • create return label I and store on stack
  • evaluate arguments and copy to formal parameters
  • insert goto to procedure beginning
  • attach label created in step 4 to statement after goto
• To handle returns:
  • if empty stack then
    • exit procedure
  • else:
    • give output parameters values from stack top
    • insert code to get return address from stack
    • remove all locals from stack
    • if function, insert code to evaluate expression and store result on stack
    • go to the return address using goto

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