Procedures call

Procedure is an important and frequently used programming construct for a compiler. It is used to generate good code for procedure calls and returns.

Calling sequence:

The translation for a call includes a sequence of actions taken on entry and exit from each procedure. Following actions take place in a calling sequence:

• When a procedure call occurs then space is allocated for activation record.
• Evaluate the argument of the called procedure.
• Establish the environment pointers to enable the called procedure to access data in enclosing blocks.
• Save the state of the calling procedure so that it can resume execution after the call.
• Also save the return address. It is the address of the location to which the called routine must transfer after it is finished.
• Finally generate a jump to the beginning of the code for the called procedure.

Let us consider a grammar for a simple procedure call statement

1. S →    call id(Elist)  
2.    Elist →   Elist, E  
3.    Elist →  E  

A suitable transition scheme for procedure call would be:

Production Rule	Semantic Action
S → call id(Elist)	for each item p on QUEUE do   GEN (param p)     GEN (call id.PLACE)
Elist → Elist, E	append E.PLACE to the end of QUEUE
Elist → E	initialize QUEUE to contain only    E.PLACE

Queue is used to store the list of parameters in the procedure call.