Three Address Code | Examples

Three Address Code-

 

Three Address Code is a form of an intermediate code.

 

The characteristics of Three Address instructions are-

  • They are generated by the compiler for implementing Code Optimization.
  • They use maximum three addresses to represent any statement.
  • They are implemented as a record with the address fields.

 

General Form-

 

In general, Three Address instructions are represented as-

 

a = b op c

 

Here,

  • a, b and c are the operands.
  • Operands may be constants, names, or compiler generated temporaries.
  • op represents the operator.

 

Examples-

 

Examples of Three Address instructions are-

  • a = b + c
  • c = a x b

 

Common Three Address Instruction Forms-

 

The common forms of Three Address instructions are-

 

1. Assignment Statement-

 

x = y op z and x = op y

 

Here,

  • x, y and z are the operands.
  • op represents the operator.

 

It assigns the result obtained after solving the right side expression of the assignment operator to the left side operand.

 

2. Copy Statement-

 

x = y

 

Here,

  • x and y are the operands.
  • = is an assignment operator.

 

It copies and assigns the value of operand y to operand x.

 

3. Conditional Jump-

 

If x relop y goto X

 

Here,

  • x & y are the operands.
  • X is the tag or label of the target statement.
  • relop is a relational operator.

 

If the condition “x relop y” gets satisfied, then-

  • The control is sent directly to the location specified by label X.
  • All the statements in between are skipped.

 

If the condition “x relop y” fails, then-

  • The control is not sent to the location specified by label X.
  • The next statement appearing in the usual sequence is executed.

 

4. Unconditional Jump-

 

goto X

 

Here, X is the tag or label of the target statement.

 

On executing the statement,

  • The control is sent directly to the location specified by label X.
  • All the statements in between are skipped.

 

5. Procedure Call-

 

param x call p return y

 

Here, p is a function which takes x as a parameter and returns y.

 

PRACTICE PROBLEMS BASED ON THREE ADDRESS CODE-

 

To solve the problems, Learn about the Precedence Relations and Associativity of Operators.

 

Problem-01:

 

Write Three Address Code for the following expression-

a = b + c + d

 

Solution-

 

The given expression will be solved as-

 

 

Three Address Code for the given expression is-

(1) T1 = b + c

(2) T2 = T1 + d

(3) a = T2

 

Problem-02:

 

Write Three Address Code for the following expression-

-(a x b) + (c + d) – (a + b + c + d)

 

Solution-

 

Three Address Code for the given expression is-

(1) T1 = a x b

(2) T2 = uminus T1

(3) T3 = c + d

(4) T4 = T2 + T3

(5) T5 = a + b

(6) T6 = T3 + T5

(7) T7 = T4 – T6

 

Problem-03:

 

Write Three Address Code for the following expression-

If A < B then 1 else 0

 

Solution-

 

Three Address Code for the given expression is-

(1) If (A < B) goto (4)

(2) T1 = 0

(3) goto (5)

(4) T1 = 1

(5)

 

Problem-04:

 

Write Three Address Code for the following expression-

If A < B and C < D then t = 1 else t = 0

 

Solution-

 

Three Address Code for the given expression is-

(1) If (A < B) goto (3)

(2) goto (4)

(3) If (C < D) goto (6)

(4) t = 0

(5) goto (7)

(6) t = 1

(7)

 

Also Read- More Problems On Three Address Code

 

To gain better understanding about Three Address Code,

Watch this Video Lecture

 

Download Handwritten Notes Here-

 

 

Next Article- Quadruples, Triples & Indirect Triples

 

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Summary
Three Address Code | Examples
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Three Address Code | Examples
Description
In compiler design, Three Address Code is a form of an intermediate code. Three Address Code Examples and Common Forms. Three Address Code is generated by the compiler for implementing code optimization.
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Gate Vidyalay
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