8.1.1 Sub-expression Elimination

The compiler does local and global common subexpression elimination, e.g.:

i = x + y + 1;  
j = x + y;

will be translated to

iTemp = x + y;  
i = iTemp + 1;  
j = iTemp;

Some subexpressions are not as obvious as the above example, e.g.:

a->b[i].c = 10;  
a->b[i].d = 11;

In this case the address arithmetic a->b[i] will be computed only once; the equivalent code in C would be.

iTemp = a->b[i];  
iTemp.c = 10;  
iTemp.d = 11;

The compiler will try to keep these temporary variables in registers.