Solution

The correct answer is (A), (B) and (D) Only

EXPLANATION:

Three-address code (TAC) is an intermediary form of source code that sits between high-level code and assembly/low-level code, often used in a compiler's intermediate representation of the source code. In TAC, all operations take at most two operands, and an assignment is performed as well. Therefore, up to three addresses (or items) are referenced in each line of code: two for the operands and one for the resulting value's assignment.

This code can be represented in special structures, including:

• Triples: In triples, the operation is defined in one row by three fields: op (the operation), arg1 and arg2 (the arguments), and result (the place to store the resulting operation). Each row, or instruction, is implicitly defined by its position in the table. So, if there is an instruction like 'sub a, b', it means 'subtract b from a'.
• Quadruples: The quadruples structure is similar to the triples structure, but it includes an additional field for the result so that each operation does not depend on its physical position in the sequence. This makes it easier to carry out transformations on the code sequence, as this additional field for the result gives more flexibility, particularly in the process of optimization.
• Indirect Triples: Indirect triples use the concept of triples but give the advantage of quadruples. It decouples the usage of an expression from its physical location in the sequence. It consists of a position-independent data structure like quadruples, which can effectively alter the sequence of expressions without modifying the triples.

The option (C) Patterns is not a known structure for representing three address codes. Therefore, the correct answer is (A), (B) and (D), or Option 2.