Simple One-Pass Compiler part II

1. Simple One-Pass Compiler part II Natawut Nupairoj, Ph.D. Department of Computer Engineering Chulalongkorn University

2. Outline • Abstract Stack Machine. • Simple Code Generation.

3. Abstract Stack Machine • Basic machine with stack only for computation. • Ex: push 10 push 5 add push 2 minus 5 2 10 15 13

4. Abstract Stack Machine • Variables • Use value from variable • r-value. • Store value to variable • l-value. k := 5 2 + k • Ex: lvalue k push 5 := push 2 rvalue k add 5 k := 5 (addr) k 5 7 2

5. Stack Manipulation • push v push v on top of stack • pop v pop v from top of stack • rvalue l push content of data l • lvalue l push address of data l • := put r-value on top to l-value below and pop both from top • copy push copy of top

6. Translation of Expression day := (1461 * y) div 4 + (153 * m + 2) div 5 + d lvalue day push 153 div push 1461 rvalue m add rvalue y mul rvalue d mul push 2 add push 4 add := div push 5

7. Translation Scheme for Simple Expression expr ::= expr + term {print(‘add’);} expr ::= expr – term {print(‘minus’);} expr ::= term term ::= 0{print(‘push 0’);} term ::= 1{print(‘push 1’);} ... term ::= 9{print(‘push 9’);}

8. Example expr + { print(‘add’) } expr term - { print(‘minus’) } 2 { print(‘push 2’) } expr term term 5 { print(‘push 5’) } 9 { print(‘push 9’) } • Input:9 – 5 + 2 • Output: • push 9 • push 5 • minus • push 2 • add

9. Translation Scheme for Simple Expression with Tokens expr ::= expr + term {print(‘add’);} expr ::= expr – term {print(‘minus’);} expr ::= term term ::= number{print(‘push ’); print(number.lexeme);} term ::= id{print(‘lvalue ); print(id.lexeme);}

10. expr ::= expr + term {print(‘add’);} expr ::= expr – term {print(‘minus’);} expr ::= term term ::= number{print(‘push ’); print(number.lexeme);} term ::= id{print(‘rvalue ’); print(id.lexeme);} Input: 2 + k – m Output: push 2 rvalue k add rvalue m minus Example

11. Translation Scheme for Assignment Statement stmt ::= id:={print(‘lvalue’); print(id.lexeme);} expr{print(‘:=‘);} • Input: k := k + 1 • Output: • lvalue k • rvalue k • push 1 • add • := expr stmt

12. Control Flow • eq pop top two values and compare, if equal push 1 on top of the stack, otherwise push 0. • lt pop top two values and compare, if bottom less than first push 1 on top of the stack, otherwise push 0. • gt similar to “lt”. • label l target for jump • goto l jump to lable l • gofalse l pop top; jump if zero • gotrue l pop top; jump if nonzero

13. Translation of if Statement stmt ::= ifexpr {out:=newlabel; print(‘gofalse’); print(out);} thenstmt1 {print(‘label ’); print(out);} • if k+1 < 0 then m := 3; • rvalue k • rush 1 • add • push 0 • lt • gofalse lb01 • lvalue m • push 3 • := • label lb01 stmt Code for expr gofalse lb01 Code for stmt1 label lb01