Code Generation 1

Organization of Storage

Code Area
Static Area
Stack Area
Heap Area

Stack Management using Register File

Stack pointer (SP): points to the top of the frame
Frame Pointer (FP, BP): points to the frame base

because stack frame size is not always known at compile time.

Saving Registers

The callee may overwrite useful values in the registers.

So caller's useful values should be stored in stack when function-call (push), and restored when callee return (pop). This role is done by both callee and caller (caller-saved, callee-saved).

Caller-saved registers used to hold temporary quantities that need not be preserved across calls.
Callee-saved registers used to hold long-lived values that should be preserved across calls.

So Code before call:

push the params.
push caller-saved registers
push return address (curr PC) and jump to callee code

Prologue of callee

push dynamic link (FP)
old stack pointer becomes new frame pointer
push callee-saved registers
push local var

Epilogue

pop callee-saved registers
store return value at appropriate place
restore old stack pointer
pop old frame pointer
pop return addr and jump to that

Code after call

pop caller-saved registers
use return value from appropriate place

When accessing stack variable, use offsets from FP.

Global Variables or Static Variables

Global variables have same references for all scope. They are assigned a fixed address once (statically allocated).

Code > Static Data > Stack

Dynamic Allocation

The dynamically allocated value outlives the procedure creating it (unless deleted).

Code > Static Data > Stack -> <- Heap

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