Variables that can be used as local variables must be declared as local variables and not as global variables. There is a possibility that the value of a global variable will be changed by function calling or pointer operations, thus the efficiency of optimization is degraded.

The following advantages are available when local variables are used.

[Example]

Case in which global variables are used for temporary variables (before improvement) and case in which local variables are used (after improvement)

Source code before improvement

int tmp;

void func(int* a, int* b)

{

     tmp = *a;

     *a = *b;

     *b = tmp;

}

Assembly-language expansion code before improvement

__func:

     MOV.L #_tmp,R4

     MOV.L [R1],[R4]

     MOV.L [R2],[R1]

     MOV.L [R4],[R2]

     RTS

Source code after improvement

void func(int* a, int* b)

{

     int tmp;

     tmp = *a;

     *a = *b;

     *b = tmp;

}

Assembly-language expansion code after improvement

__func:

     MOV.L [R1],R5

     MOV.L [R2],[R1]

     MOV.L R5,[R2]

     RTS