Passing parameters and the return value using registers

When a compiler processes a function definition:

int f( int[] A, int a, int b ) { .... }

When registers are used for parameter passing, the compiler will:

Designate (= assign/reserve) a register for the parameter

Example:

Function f: Parameter Name Data Type Location ------------------------------------------------ 0 A int[ ] r0 1 a int r1 2 b int r2

Note: the return value is usually returned in register r0 by compilers - we will adopt this.

How is header information used ?

The information in the function header is used to:

Map the variables in the function body to its corresponding designated registers
Use the designated registers as operands in the translation of the function body

Example: since the parameter a was designated as register r1, a statement using variable a will use register r1

int f( int[] A, int a, int b ) { .... Translated as a = a + 1; ----------------> add r1, r1, #1 .... }