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)
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