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What is Three Address Code

August 2, 2023

2 min read

Three Address Code (TAC) is an intermediate code generation technique used by compilers to represent high-level language constructs in a lower-level, more manageable form. TAC is called “three address code” because each instruction in this intermediate representation typically involves at most three addresses or operands. These addresses can represent variables, constants, or temporary results. TAC is an essential part of the compilation process as it simplifies the optimization and code generation phases.

Characteristics of Three Address Code

  1. Simplicity: TAC uses a simple and limited set of instructions, making it easier to analyze and optimize.
  2. Efficiency: TAC strikes a balance between high-level language constructs and low-level machine instructions, allowing for efficient code generation.
  3. Flexibility: TAC can represent a wide range of programming constructs, including arithmetic operations, control flow statements, and function calls.
  4. Ease of Optimization: The simplicity of TAC makes it easier for compilers to apply various optimization techniques to improve the performance of the generated code.

Basic Structure of TAC

A typical TAC instruction consists of at most three operands, which can be variables, constants, or temporary values. The general format of a TAC instruction is as follows:

result = operand1 operator operand2

Here, result is the variable or temporary location where the result of the operation is stored, operand1 and operand2 are the input operands, and operator is the operation to be performed (e.g., +, -, *, /).

Example

Consider the following high-level code snippet:

a = b + c * d;

The corresponding TAC representation might look like this:

t1 = c * d
a = b + t1

In this example, t1 is a temporary variable used to store the result of the multiplication before it is added to b.

Conclusion

Three Address Code is a valuable intermediate representation used by compilers to bridge the gap between high-level programming languages and low-level machine code. Its simplicity, efficiency, and flexibility make it an ideal choice for optimizing and generating code for a wide range of programming constructs. Understanding TAC is essential for anyone interested in compiler design and implementation.