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
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.
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