Embedded C language pointer alias

1、 Pointer alias

（1） When two pointers point to the same object , These two pointers are called aliases of the object

（2） Compiler features

① The compiler is pessimistic

② The compiler does not know whether the pointer is an alias

2、 example ： Step and accumulate the two timers

void timers_v1(int *timer1,int *timer2, int *step)

{

        *timer1 += *step;

        *timer2 += *step;

}

The assembly code of the above code is ：

timers_v1.s

        LDR r3,[r0,#0]        ;r3=*timer1

        LDR r12,[r2,#0]        ;r12=*step

        ADD r3,r3,r12        ;r3+=r12

        STR   r3,[r0,#0]        ;*timer1=r3

        LDR r0,[r1,#0]        ;r0=*timer2

        LDR r2,[r2,#0]        ;r2=*step

        ADD r0,r0,r12        ;r0+=r12

        STR   r0,[r1,#0]        ;*timer2=r0

        MOV pc,r14               ;return 

*step Variable loaded twice

3、 reflection ： What measures can be taken to avoid reading memory twice ？

4、 Code improvements ： Add local variables , cache *step Value , Use temporary variables for subsequent operations .

void timers_v2(int *timer1,int *timer2, int *step)

{

        int step = *step;

        *timer1 += step ;

        *timer2 += step;

}