In compiler design, intermediate code acts as a bridge between the high-level source code written in a programming language and the low-level machine code understood by the computer's processor. It's a machine-independent representation of the program that simplifies the compilation process and offers several advantages:
Portability: By using intermediate code, the compiler's front-end (analysis phase) can remain independent of the target machine. This allows the same front-end to translate code from various high-level languages into the same intermediate code, while the back-end (synthesis phase) specifically generates machine code for the target architecture. This eliminates the need for a separate compiler for every machine, promoting portability.
Optimization: Intermediate code provides a convenient intermediary for applying code optimization techniques. These optimizations can be targeted towards the intermediate code itself, making them independent of the specific target machine and potentially more efficient.
Code Generation: Generating machine code from the intermediate code becomes simpler due to its standardized and machine-independent nature. The back-end can focus on translating the well-defined intermediate code instructions into the specific instruction set of the target machine.
Here are some common types of intermediate code:
- Three-address code (TAC): A basic yet effective format where each instruction has at most three operands (two sources and one destination). This explicit representation makes it easy to analyze and optimize the code.
- Postfix notation: Similar to TAC, postfix notation expresses an operation by placing the operator after its operands (e.g.,
a b +). This linear representation simplifies code generation. - Syntax tree: While not strictly code, an annotated syntax tree can serve as an intermediate representation, capturing the program's structure and semantics for further processing.
- Bytecode: A higher-level intermediate code used in platforms like Java and the .NET Framework. Bytecode is a machine-independent instruction set specifically designed for execution by a virtual machine, offering portability and security benefits.
Overall, intermediate code plays a crucial role in compiler design by facilitating efficient and portable code generation while enabling effective optimization techniques.