Chapter 9: Translation 1

Compiler Designs and Constructions

Chapter 9: TranslationObjectives:

Translation MethodThree Address Code

Dr. Mohsen Chitsaz

Chapter 9: Translation 2

Bottom-up evaluation of S-attributed:

Definitions: Syntax-directed definition with only

synthesized attributes is called S-attributed Use LR Parser

Implementation: Stack to hold info about subtrees that have

been parsed

Chapter 9: Translation 3

Example:

A.a:= F(X.x, Y.y, Z.z) for productionA ---> XYZ

State Value

X X.x

Y Y.y

Z Z.z A A.a

<--- Top

After Parse===>

Value of Symbol Table

Pointer to a State in LR(1) Parse Table

Chapter 9: Translation 4

Example:

Production Semantic Values (Code)L ---> E$ Print (Val[Top])

E ---> E + T Val[nTop]:= Val[Top – 2] + Val[Top]

E ---> T

T ---> T * F Val[nTop]:= Val[Top – 2] * Val[Top]

T ---> F

F ---> (E) Val[nTop]:=Val[Top – 1]

F ---> digit

Chapter 9: Translation 5

Cont.

Using LR Parser: Parse 3 * 5 + 4 $

T.Val

+

E.Val E.Val

<--- Top Top – 1 Top - 2 <--- nTop

=

Chapter 9: Translation 6

Input Stack Attribute Production Used

3 * 5 + 4 $ - -

* 5 + 4 $ 3 3

* 5 + 4 $ F 3 F ---> digit

* 5 + 4 $ T 3 T ---> F

5 + 4 $ T * 3

+ 4 $ T * 5 3 * 5

+ 4 $ T * F 3 * 5 F - digit

+ 4 $ T 15 T ---> T * F

+ 4 $ E 15 E ---> T

4 $ E + 15

$ E + 4 15 + 4

$ E + F 15 + 4 F ---> digit

$ E + T 15 4 T ---> F

$ E 19 E ---> E + T

E 19

L 19 L ---> E $

Chapter 9: Translation 7

Parse 3 * 5 + 4 $L

E $

E + T

FT

* FT

5F

3

Show Stack

4

Chapter 9: Translation 8

Intermediate Code Generation:

Type of intermediate code generation:1. Graphical Representation

a := b * c + b * c Syntax Tree

:=

a +

* *

b c b c

Chapter 9: Translation 9

Dag

:=

a +

*

b c

Chapter 9: Translation 10

Advantages? Disadvantages?

Chapter 9: Translation 11

Representation of Syntax Tree:

:=

id a +

* *

id c id bid b id c

<--- b * c

a-

Chapter 9: Translation 12

b. Using array

0 id b

1 id c

2 * 0 1

3 id b

4 id c

5 * 3 4

6 + 2 5

7 id a

8 := 7 6

b * c

b * c

Chapter 9: Translation 13

2. Postfix notation ( a:= ((b * c) + (b * c)))

a b c * b c * + :=

Advantages/Disadvantages?- No need for ()- No need for Temp- Use Run-Time Stack- Easy to reconstruct Parse Tree

Chapter 9: Translation 14

Three Address Code:

3. Three address Code:General Form

X := A op BX, A, B are Const, Name, or Temp

Example: a := b * c + d

T0 := b * c

T1 := T0 + d

a := T1

Chapter 9: Translation 15

Three Address Code: Advantages? Disadvantages?

Chapter 9: Translation 16

Three Address Code: Assignment

Operand:= Operand1 op Operand2 Unary Operation

Operand:= Op Operand1 Copy Statement

Operand:= Operand1 Procedure/Function Call

Parm A,BCall P,n

Chapter 9: Translation 17

Three Address Code Indexed Assignment

Operand[I]:= B Pointer

A:= Address B Unconditional Jump

GOTO L Conditional Jump

If A RelOp B GOTO L

Chapter 9: Translation 18

Types of Three Address Codes:

1. Quadruples (Quad/Three Address Code)

Record structure with 4 fieldsArg1, Arg3, op, Result

Example: a:= -b+c*d

Chapter 9: Translation 19

Quadruples:

op Arg1 Arg2 Result

0 U_Minus b T1

1 * c d T2

2 + T1 T2 T3

3 := T3 a

4Code: U_Minus b T1

Mul c d T2

Add T1 T2 T3

Assign T3 a

Chapter 9: Translation 20

Types of Three Address Codes:

2. Triples: (3 – Tuples/Triplest)Record with 3 fieldsArg1, Arg2, op

Example: a := -b + c * d

op Arg1 Arg2

(0) U_Minus b

(1) * c d

(2) + (0) (1)

(3) := (2) a

Chapter 9: Translation 21

Triples: Arg1, Arg2 are either a pointer to Symbol

Table (Name, Constant) or a pointer to Triple Structure

This is a Two Address Instruction Most Assembly Languages are made up of

Triples

Chapter 9: Translation 22

3. Indirect Tuples:We use pointers to TriplesExample: a:= -b + c * d

Triple Address op Arg1 Arg2

0 14 14 U_Minus b

1 15 15 * c d

2 16 16 + (14) (15)

3 17 17 := (15) a

Chapter 9: Translation 23

Indirect Tuples:

Save Space: Why? Not good for optimizing code: Why? Not good for memory assignment prior

to code generation