Three Address Code For Array Examples

Tag: Three Address Code For Array Examples

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

{

if (a < b) then

x++;

else

x–;

c++;

} while (c < 5)

Solution-

Three address code for the given code is-

c = 0
if (a < b) goto (4)
goto (7)
T1 = x + 1
x = T1
goto (9)
T2 = x – 1
x = T2
T3 = c + 1
c = T3
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-

if (A < C) goto (3)
goto (15)
if (B > D) goto (5)
goto (15)
if (A = 1) goto (7)
goto (10)
T1 = c + 1
c = T1
goto (1)
if (A <= D) goto (12)
goto (1)
T2 = A + B
A = T2
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-

a = b + c
t1 = a x a
b = t1 + a
c = t1 x b
t2 = c + b
a = t2 + t2

Solution-

Directed acyclic graph for the given three address code is-

Problem-05:

Consider the following code-

prod = 0 ;

i = 1 ;

{

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

i = i + 1 ;

} while (i <= 10) ;

Compute the three address code.
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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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

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