Three Address Code-

 

Before you go through this article, make sure that you have gone through the previous article on Three Address Code.

 

We have discussed-

• Three Address Code is a form of an intermediate code.
• It is generated by the compiler for implementing Code Optimization.
• It uses maximum three addresses to represent any statement.

 

In this article, we will discuss Implementation of Three Address Code.

 

Implementation-

 

Three Address Code is implemented as a record with the address fields.

 

The commonly used representations for implementing Three Address Code are-

 

 

1. Quadruples
2. Triples
3. Indirect Triples

 

1. Quadruples-

 

In quadruples representation, each instruction is splitted into the following 4 different fields-

op, arg1, arg2, result

Here-

• The op field is used for storing the internal code of the operator.
• The arg1 and arg2 fields are used for storing the two operands used.
• The result field is used for storing the result of the expression.

 

Exceptions   There are following exceptions-   Exception-01:   To represent the statement x = op y, we place- op in the operator field y in the arg1 field x in the result field arg2 field remains unused   Exception-02:   To represent the statement like param t1, we place- param in the operator field t1 in the arg1 field Neither arg2 field nor result field is used   Exception-03:   To represent the unconditional and conditional jump statements, we place label of the target in the result field.

 

2. Triples-

 

In triples representation,

• References to the instructions are made.
• Temporary variables are not used.

 

3. Indirect Triples-

 

• This representation is an enhancement over triples representation.
• It uses an additional instruction array to list the pointers to the triples in the desired order.
• Thus, instead of position, pointers are used to store the results.
• It allows the optimizers to easily re-position the sub-expression for producing the optimized code.

 

PRACTICE PROBLEMS BASED ON QUADRUPLES, TRIPLES & INDIRECT TRIPLES-

 

Problem-01:

 

Translate the following expression to quadruple, triple and indirect triple-

a + b x c / e ↑ f + b x c

 

Solution-

 

Three Address Code for the given expression is-

 

T1 = e ↑ f

T2 = b x c

T3 = T2 / T1

T4 = b x a

T5 = a + T3

T6 = T5 + T4

 

Now, we write the required representations-

 

Quadruple Representation-

 

Location	Op	Arg1	Arg2	Result
(0)	↑	e	f	T1
(1)	x	b	c	T2
(2)	/	T2	T1	T3
(3)	x	b	a	T4
(4)	+	a	T3	T5
(5)	+	T5	T4	T6

 

Triple Representation-

 

Location	Op	Arg1	Arg2
(0)	↑	e	f
(1)	x	b	c
(2)	/	(1)	(0)
(3)	x	b	a
(4)	+	a	(2)
(5)	+	(4)	(3)

 

Indirect Triple Representation-

 

	Statement
35	(0)
36	(1)
37	(2)
38	(3)
39	(4)
40	(5)

 

Location	Op	Arg1	Arg2
(0)	↑	e	f
(1)	x	b	e
(2)	/	(1)	(0)
(3)	x	b	a
(4)	+	a	(2)
(5)	+	(4)	(3)

 

Problem-02:

 

Translate the following expression to quadruple, triple and indirect triple-

a = b x – c + b x – c

 

Solution-

 

Three Address Code for the given expression is-

 

T1 = uminus c

T2 = b x T1

T3 = uminus c

T4 = b x T3

T5 = T2 + T4

a = T5

 

Now, we write the required representations-

 

Quadruple Representation-

 

Location	Op	Arg1	Arg2	Result
(1)	uminus	c		T1
(2)	x	b	T1	T2
(3)	uminus	c		T3
(4)	x	b	T3	T4
(5)	+	T2	T4	T5
(6)	=	T5		a

 

Triple Representation-

 

Location	Op	Arg1	Arg2
(1)	uminus	c
(2)	x	b	(1)
(3)	uminus	c
(4)	x	b	(3)
(5)	+	(2)	(4)
(6)	=	a	(5)

 

Indirect Triple Representation-

 

	Statement
35	(1)
36	(2)
37	(3)
38	(4)
39	(5)
40	(6)

 

Location	Op	Arg1	Arg2
(1)	uminus	c
(2)	x	b	(1)
(3)	uminus	c
(4)	x	b	(3)
(5)	+	(2)	(4)
(6)	=	a	(5)

 

To gain better understanding about Quadruples, Triples and Indirect Triples,

Watch this Video Lecture

 

Download Handwritten Notes Here-

 

 

Next Article- Basic Blocks and Flow Graphs

 

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