Three code generation, Quadruples, Triple, indirect triple

1. Three Address Code
Pooja Dixit
Department of Computer Science
Sophia Girls’ College (Autonomous),
Ajmer

2. Three address code
• Three-address code is an intermediate code. It is used by the
optimizing compilers.
• In three-address code, the given expression is broken down into
several separate instructions. These instructions can easily
translate into assembly language.
• In three address code, at most three addresses are used to
represent any statement.
• Each Three address code instruction has at most three
operands. It is a combination of assignment and a binary
operator.
• Example : Given Expression:
a := b op c
Where-
▫ a, b, c are operands
▫ Op= operators
• Example: a = b + c
▫ Here a, b, c = Operands
▫ +, = are Operator

3. How to Generate Three address code
• Eg:- a = b + c + d
this given expression has two operator +, =
Note: to generate 3-add code for given expression we
have follow these rules-
• ‘+’ operator has higher precedence over ‘=’ operator.
• ‘+’ operator is left associative.
• So the Address Code will be-
▫ T1 = b + c
▫ T2 = T1 + d
▫ a = T2
b + c + d
1
2
3
a =
According to the rule we
first solve b + c, than solve
d and at last store result
into a

4. Implementation of Three Address Code
• Three address code can be implemented as a record with the
address fields.
• There are three types of representation used for three
address code.
Representation
Quadruple
Triple
Indirect Triple

5. Implementation of Three Address Code –
1. Quadruple –
in quadruples representation each instruction is
divided into 4 fields.
Where-
▫ The op field is used to represent the internal code
for operator.
▫ The ag1, ag2 fields represent the two operands used.
▫ The result field is used to store the result of an
expression.
Operator
arg1
arg2
results

6. Three Address Code
• Example
• Change this expression into three-address code:
▫ t1 := e f
▫ t2 := b * c
▫ t3 := t2 / t1
▫ t4 := b * a
▫ t5 := a + t3
▫ t6 := t5 + t4
• These statements are represented by quadruples as follows:
• Operator Source 1 Source 2 Destination
(0) e f T1
(1) * b c T2
(2) / T2 T1 T3
(3) * b a T4
(4) + a T3 T5
(5) + T5 T4 T6
Note: here we arrange the terms according to the
Operator priority

7. Implementation of Three Address Code –
• Advantage –
▫ Easy to rearrange code for global optimization.
▫ One can quickly access value of temporary variables
using symbol table.
• Disadvantage –
▫ Contain lot of temporaries.
▫ Temporary variable creation increases time and
space complexity.

8. Triples
• The triples have three fields to implement the three address code. The
field of triples contains the name of the operator, the first arg1 operand
and the second arg2 operand.
• In triple representation the use of temporary variables are avoided and
instead to instructions are made.
Fig: Triples field
Operator
arg1
arg2

9. Triples
Example: consider the example of quadruple
• Three address code are same as quadruple
• These statements are represented by triples as follows:
• If there is any statement suffle
Operator Arg 1 Arg 2
(0) e f
(1) * b c
(2) / (1) (0)
(3) * b a
(4) + a (2)
(5) + (4) (3)

10. Indirect Triples
• This representation is an enhancement over triples representation. It
use an additional instruction array to list the pointers to the desired
order.
• Thus it use pointers instead of position to store result which enable the
optimizers to freely reposition the sub expression to produce an
optimize code.
Operator Arg 1 Arg 2
(0) e f
(1) * b c
(2) / (1) (0)
(3) * b a
(4) + a (2)
(5) + (4) (3)
Statement
35 (0)
36 (1)
37 (2)
38 (3)
39 (4)
40 (5)