Tag: How to write Three Address Code for a Program

Miscellaneous Problems in Compiler Design

Compiler Design

Three Address Code | DAGs | Basic Blocks & Flow Graphs-

 

Before you go through this article, make sure that you have gone through the previous articles on-

 

In this article, we will solve Miscellaneous Problems based on these Concepts.

 

PRACTICE PROBLEMS BASED ON ABOVE CONCEPTS-

 

Problem-01:

 

Generate three address code for the following code-

 

c = 0

do

{

if (a < b) then

x++;

else

x–;

c++;

} while (c < 5)

 

Solution-

 

Three address code for the given code is-

  1. c = 0
  2. if (a < b) goto (4)
  3. goto (7)
  4. T1 = x + 1
  5. x = T1
  6. goto (9)
  7. T2 = x – 1
  8. x = T2
  9. T3 = c + 1
  10. c = T3
  11. if (c < 5) goto (2)

 

Problem-02:

 

Generate three address code for the following code-

 

while (A < C and B > D) do

if A = 1 then C = C + 1

else

while A <= D

do A = A + B

 

Solution-

 

Three address code for the given code is-

  1. if (A < C) goto (3)
  2. goto (15)
  3. if (B > D) goto (5)
  4. goto (15)
  5. if (A = 1) goto (7)
  6. goto (10)
  7. T1 = c + 1
  8. c = T1
  9. goto (1)
  10. if (A <= D) goto (12)
  11. goto (1)
  12. T2 = A + B
  13. A = T2
  14. goto (10)

 

Problem-03:

 

Generate three address code for the following code-

 

switch (ch)

{

case 1 : c = a + b;

break;

case 2 : c = a – b;

break;

}

 

Solution-

 

Three address code for the given code is-

 

if ch = 1 goto L1

if ch = 2 goto L2

L1:

T1 = a + b

c = T1

goto Last

L2:

T1 = a – b

c = T2

goto Last

Last:

 

Problem-04:

 

Construct a DAG for the following three address code-

  1. a = b + c
  2. t1 = a x a
  3. b = t1 + a
  4. c = t1 x b
  5. t2 = c + b
  6. a = t2 + t2

 

Solution-

 

Directed acyclic graph for the given three address code is-

 

 

Problem-05:

 

Consider the following code-

 

prod = 0 ;

i = 1 ;

do

{

prod = prod + a[ i ] x b[ i ] ;

i = i + 1 ;

} while (i <= 10) ;

 

  1. Compute the three address code.
  2. Compute the basic blocks and draw the flow graph.

 

Solution-

 

Part-01:

 

Three address code for the given code is-

 

prod = 0

i = 1

T1 = 4 x i

T2 = a[T1]

T3 = 4 x i

T4 = b[T3]

T5 = T2 x T4

T6 = T5 + prod

prod = T6

T7 = i + 1

i = T7

if (i <= 10) goto (3)

 

Part-02:

 

Step-01:

 

We identify the leader statements as-

  • prod = 0 is a leader because first statement is a leader.
  • T1 = 4 x i is a leader because target of conditional or unconditional goto is a leader.

 

Step-02:

 

The above generated three address code can be partitioned into 2 basic blocks as-

 

 

Step-03:

 

The flow graph is-

 

 

To gain better understanding about these Miscellaneous Problems,

Watch this Video Lecture

 

Download Handwritten Notes Here-

 

Next Article- Code Optimization

 

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Watch video lectures by visiting our YouTube channel LearnVidFun.

Three Address Code | Examples

Compiler Design

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

 

Get more notes and other study material of Compiler Design.

Watch video lectures by visiting our YouTube channel LearnVidFun.