Phases of a Compiler: What You Need To Know / Roman Samborskyi

As you might expect, a lot happens when you run the command to compile your code on the terminal or click the build button in your preferred IDE (integrated development environment). Compilers work diligently behind the scenes to convert the code you write into machine language that your device can comprehend and execute. But exactly how do compilers accomplish this? What are the various stages of the compiler involved in the process?

These are the types of queries that every new programmer or student of software development has. To help you better grasp this crucial step in software development, we’ll be going over the stages of a compiler in this post, from lexical analysis to code generation.

Main Phases of a Compiler

The analysis phase and the synthesis phase are typically the two main steps of compilers. The compiler reads and examines the source code during the analysis phase to determine its structure and semantics. The compiler produces machine code from the examined source code during the synthesis stage.

Compilers are sometimes split into two modules—the front-end and the back-end—to carry out these duties. The front-end module is in charge of the analysis phase and is in charge of examining the syntax and semantics of the source code. The synthesis phase is managed by the back-end module, which also creates the machine code.

The six stages of a compiler that we’ll examine are divided across the two modules. Lexical analysis, syntactic analysis, and semantic analysis are handled by the front-end module, whereas intermediate code generation, code optimization, and code creation are handled by the back-end module.

After covering the fundamentals, let’s delve deeper into how each of the six stages functions.

Lexical Analysis

Lexical analysis is the first stage of the analysis phase. The source code is scanned by the compiler during this phase, which involves breaking it up into tokens to make it easier to analyze.

Words or symbols that are used as tokens in programming languages can have a specific meaning. They consist of the fundamental components of the code, such as operators, identifiers, and keywords. For instance, the semicolon (;) is a character used to indicate the end of a statement in the C programming language.

Character by character, the lexical analyzer reads the source code and organizes the characters into tokens according to established rules. The lexical analyzer, for instance, would group the characters int x = 5; into the tokens int, x, =, 5, and ; if it came across those characters.

As part of its preliminary tests, lexical analysis also eliminates comments and whitespace and looks for any incorrect characters or keywords.

The first phase of compiling is Lexical Analysis, where the code is broken up into tokens.

Syntax Analysis

Syntax analysis comes next after lexical analysis. Here, the compiler creates parse trees in preparation for the parsing process while checking for grammatical and syntactic issues. Parse trees depict the code’s structure and demonstrate the relationships between its many tokens.

The syntax analyzer determines whether the tokens produced by the lexical analyzer adhere to the language’s grammar rules. When a syntax error is encountered, it generates an error message, halts compilation, and informs the programmer.

Additionally, syntax analysis finds any syntax mistakes in the code and informs the developer. For instance, the compiler will detect this as a syntax error and alert the developer if they neglect to include a semicolon at the end of a statement. It then creates a parse tree that depicts the structure of the source code if there are no syntax problems.

Semantic Analysis

The third phase, known as semantic analysis, focuses on finding semantic flaws and creating a preliminary version of the source program. Semantic errors are those that happen when the syntax of the source code is correct but the meaning is incorrect.

An annotated syntax tree is the name given to the intermediate representation. It is a data structure that, as opposed to the source code, describes the code in a more abstract manner. The semantic analyzer looks for semantic mistakes in the parse tree that the syntax analyzer has produced.

It also does type checking and checks for undeclared variables. The latter verifies the compatibility of the different variables and expression types used in the source code.

Intermediate Code Generation

The compiler creates an intermediate representation of the source program after making sure there are no semantic problems. In the following stage, the code generator makes use of this interim code representation. Intermediate code is a simplified version of the source code that is simpler to read, understand, and modify than the original source code.

The parse tree previously produced by the semantic analyzer is the first thing the intermediate code generator uses. The intermediate code is then generated using it. There are other kinds of intermediate codes, such as three-address codes (TAC), which only use three operands to express each instruction. Another popular type of intermediate code is postfix notation, which describes expressions in a way that makes them simpler to evaluate with a stack-based algorithm.

The intermediate code can then be further optimized by the compiler to improve the effectiveness and functionality of the output machine code.

Code Optimization

The goal of code optimization is to increase the functionality of the machine code that the compiler produces. It functions somewhat like fine-tuning the code to help it run more quickly and effectively.

Therefore, code optimization is a crucial stage of the compiler since it has the potential to greatly enhance the efficiency of the produced code. The optimization process can involve straightforward methods like constant folding and algebraic simplification or sophisticated algorithms that completely reorganize the program.

The compiler examines the intermediate code during the code optimization stage to find patterns and redundant operations in order to reduce the number of instructions. The intermediate code is subsequently transformed by the compiler to increase performance while keeping the program’s functionality. Depending on the target platform and the kind of program being compiled, the compiler will execute a variety of optimizations.

For instance, the compiler can unroll a loop that iterates over an array to make it more efficient. This indicates that it produces code that runs the loop repeatedly in a single operation. Constant folding, which evaluates expressions with constant values at compile-time rather than run-time, is another function the compiler is capable of performing. Overall, code optimization can decrease code overhead and enhance program performance.

One of the important phases of compiling is code optimization.

Code Generation

Code generation is the compiler’s last stage. Here, the compiler converts the machine language-optimized intermediate code. The compiler creates machine instructions during the code generation stage that match the intermediate code.

Allocating memory, controlling registers, and producing assembly code are all steps in the code generation process. The compiler’s code generation phase creates executable code that can be run on the target platform, making sure it functions as effectively as feasible.

Phases of a Compiler: Wrapping Up

A crucial stage in the development of software applications is the compilation of source code into machine language. Compilers may appear to be sophisticated tools, but they aren’t in the true sense. We can more easily grasp the compilation process if we break it down into the separate phases of the compiler. Each stage, from lexical analysis to code generation, is essential to ensuring that the final executable code is effective and error-free.

Compilers come in a variety of forms, each having special characteristics and skills of its own. Others are tailored for certain hardware architectures, while some compilers are created for specific programming languages. For instance, the GCC (GNU Compiler Collection) is a compiler system that supports C, C++, and Fortran among other programming languages.

Other languages have their own compilers, including Swift and Java. Java source code is converted into bytecode by the Java compiler. Any platform with a Java Virtual Machine may run Bytecode. Swift has its own compiler; it is a relatively new programming language created by Apple. It transforms Swift code into machine code that is optimized for use with iOS, macOS, and other Apple platforms.

In conclusion, by comprehending the various stages of a compiler, you can better grasp how it functions and how you might be able to develop more effective code that would produce fewer compilation errors.

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