Yet More Code Generation

For the next week or so, I will be picking out concepts from section 8.3-8.7 and Chapter 9 that apply to our project. Please be reading these sections.

Assignment Statements

We have looked at basic assignment statements of the form:

a = 100;
a = a + 1;
a = b + c / d;
...
In general, we know that an assignment statement of the form:

a = b + c;
emits the following code:

t1 = b + c
a = t1
If the expression (e.g. b + c) is more complicated, we require more temporary variables remembering for now, we are not concerned about reusing temporary variable names.

I am not going to discuss every possible combination of assignment statements we might have, but I will discuss each of the following statements:

1) a = &b;   
2) *p = a;  
3) a[b] = c; 
4) a = b++;
So what might the code for each of the above statements look like given our runtime environment?

1) a = &b;

Draw a picture using basic memory that reflects this statement. Consider:

main ()
{
  int *a, b;

  b = 100;
  a = &b;
}

[ryand@Huskers compiler]$ pcc  z.c
  1    main ()
  2    {
  3      int *a, b;
  4    
  5      b = 100;
  6      a = &b;
  7    }

[ryand@Huskers compiler]$ more z.q 
 1  27   0   0   0   0   0   0
 2  22   0   3   0   0   0   0
 2  26   2   1   0   0   3   2
 2  26   3   2   0   0   3   3
 2  26   4   3   0   0   3   1
 2  23   0   0   0   0   0   0
 1  21   0   0   0   0   0   1
 1  28   0   0   0   0   0   0
2
0
100
2) *p = a;

Draw a picture using basic memory that reflects this statement. Consider:


  1   main ()
  2   {
  3     int *p, a;
  4
  5     a = 100;
  6     *p = a;
  7     output(*p,a);
  8   }

[ryand@Huskers compiler]$ more quadfile
 1  27   0   0   0   0   0   0
 2  22   0   3   0   0   0   0
 2  26   2   1   0   0   3   2
 2  26   4   2   0   0   4   1
 2   9   4   1   0   0   3   3
 2  20   4   2   0   0   0   0
 2  20   4   3   0   0   0   0
 2  25   0   2   0   0   0   0
 2  26   0   0   0   0   1   0
 2  23   0   0   0   0   0   0
 1  21   0   0   0   0   0   1
 1  28   0   0   0   0   0   0
2
0
100

[ryand@Huskers compiler]$ inter a s

______________________________________________________________
TRACE: sp = 1, pc = 0, ap = 0
TRACE: quad = 27 0 0 0 0 0 0
TRACE: operand1 = 0, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0A  100S    0     0     0     0     0     0     0     0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 1, pc = 10, ap = 0
TRACE: quad = 21 0 0 0 0 0 1
TRACE: operand1 = 0, operand2 = 0, operand3 = 1
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0A  100S    0     0     0     0     0     0     0     0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 4, pc = 1, ap = 4
TRACE: quad = 22 0 3 0 0 0 0
TRACE: operand1 = 3, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0   100     0    11     0S    0     0     0     0     0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 7, pc = 2, ap = 4
TRACE: quad = 26 2 1 0 0 3 2
TRACE: operand1 = 100, operand2 = 0, operand3 = 6
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0   100     0    11     0A    0     0     0S    0     0 

TRACE: sp = 7, pc = 3, ap = 4
TRACE: quad = 26 4 2 0 0 4 1
TRACE: operand1 = 100, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0   100     0    11     0A    0   100     0S    0     0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 7, pc = 4, ap = 4
TRACE: quad = 9 4 1 0 0 3 3
TRACE: operand1 = 0, operand2 = 0, operand3 = 7
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

  100   100     0    11     0A    0   100     0S    0     0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 7, pc = 5, ap = 4
TRACE: quad = 20 4 2 0 0 0 0
TRACE: operand1 = 100, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

  100   100     0    11     0A    0   100   100S    0     0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 8, pc = 6, ap = 4
TRACE: quad = 20 4 3 0 0 0 0
TRACE: operand1 = 100, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

  100   100     0    11     0A    0   100   100   100S    0 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 9, pc = 7, ap = 4
TRACE: quad = 25 0 2 0 0 0 0
TRACE: operand1 = 2, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

  100   100     0    11     0A    0   100   100   100   100S

_______________________________________________________________
output:    100,   100

TRACE: sp = 7, pc = 8, ap = 4
TRACE: quad = 26 0 0 0 0 1 0
TRACE: operand1 = 0, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

  100   100     0    11     0A    0   100   100S  100   100 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 7, pc = 9, ap = 4
TRACE: quad = 23 0 0 0 0 0 0
TRACE: operand1 = 0, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0   100     0    11     0A    0   100   100S  100   100 

_______________________________________________________________
_______________________________________________________________
TRACE: sp = 1, pc = 11, ap = 0
TRACE: quad = 28 0 0 0 0 0 0
TRACE: operand1 = 0, operand2 = 0, operand3 = 0
TRACE: enter [s = stackdump b = breakpoint  = step]: s

_______________________________________________________________
                  R U N T I M E   S T A C K

    0A  100S    0    11     0     0   100   100   100   100 

_______________________________________________________________
Normal Termination






© Douglas J. Ryan / ryandj@pacificu.edu