Compiler Design and Construction - Old Questions

9.  What do you mean by three-address code representation? Explain with example.

Three address code is a type of intermediate code which is easy to generate and can be easily converted to machine code.It makes use of at most three addresses and one operator to represent an expression and the value computed at each instruction is stored in temporary variable generated by compiler.

There are 3 representations of three address code:

1. Quadruples:
It is structure with consist of 4 fields namely op, arg1, arg2 and result. op denotes the operator and arg1 and arg2 denotes the two operands and result is used to store the result of the expression. The three address statements x = y op z is represented by placing y in arg1, z in arg2 and x in result. For e.g. for statement a = b*-c +b*-c , the quadruples is:

2. Triples:

This representation doesn’t make use of extra temporary variable to represent a single operation instead when a reference to another triple’s value is needed, a pointer to that triple is used. So, it consist of only three fields namely op, arg1 and arg2. For e.g. for statement a = b*-c +b*-c , the triples is:

3. Indirect triples:
This representation makes use of pointer to the listing of all references to computations which is made separately and stored. It involves in listing of pointers to triples rather than listing of triples themselves. For e.g. the three address indirect triples for same statement above is