“From Code to Program”: Unveiling the Hidden Stages of Compiler Design
Have you ever wondered how your favourite software programs are created? One key ingredient in the process is a tool called a compiler, which takes high-level programming code and transforms it into executable programs that can run on your computer or mobile device. But how exactly does a compiler work, and what stages are involved in its design?
In this blog, we’ll take a closer look at the various stages that go into building a compiler, from the initial parsing of source code to the generation of machine-readable code. We’ll explore the challenges that must be overcome at each step and discuss the techniques and algorithms developed to optimize and streamline the process, maybe a bit more in the upcoming blogs.
Whether you’re a seasoned software developer or simply curious about the inner workings of your favourite apps, this blog will provide a comprehensive overview of compiler design and the critical stages involved. So let’s dive in and explore the fascinating world of compiler technology!
Introduction
To begin with, let’s start with what a compiler actually is. Now, before we get into that, we have something called as a translator. In compiler design, a translator refers to a software program or tool that converts one form of code or language into another. The term “translator” is often used interchangeably with “compiler”, “interpreter”, and “assembler”.
A compiler is a type of translator that takes the entire source code written in a high-level programming language and converts it into an executable machine code or object code, which can be directly executed by the computer. The translation process involves several stages, such as lexical analysis, syntax analysis, semantic analysis, code generation, and code optimization. An important role of the compiler is to report any errors in the source program that it detects during translation process.
An interpreter, on the other hand, is a type of translator that converts and executes the source code line by line, rather than converting the entire code into machine code beforehand. Interpreters are commonly used for scripting languages, such as JavaScript and Python.
An assembler is a type of translator that converts assembly language code into machine code or object code, which can be directly executed by the computer. Assemblers are often used for low-level programming and system software development.
A transcompiler is a language processor that translates source code from one high-level language to another.
Now in one look, you may feel like compilers and interpreters are almost the same. And they to an extend are. There are a few distinguishing factors that come in which separates a compiler from an interpreter.
With that said, now a days we have a mix of both, called as Hybrid Compilers which combines the essence of both compilation and interpretation. An example of such language is Java. Now at least in the case of Java which is written in a high-level programming language, it is first compiled into an intermediate bytecode format by the Java Compiler. Bytecode, for those of you who don’t know is simply a platform independent code that can run on any computer with the help of Java Virtual Machine (JVM). During runtime, the JVM interprets the bytecode and then converts it into computer executable machine code. This process is what we call as Just-In-Time compilation, as JVM compiles the machine code while it is being executed. Now this hybrid approach is what makes Java special. It combines the power of compiler’s syntax and semantic error identification and provides a level of optimization while the interpreter’s side ensure that the code can run on any platform.
In its essence, a compiler is a translator that allows programmers to write code in a language that is more natural to them and then automatically converts it into a language that the computer can understand and execute. This process makes it much easier for humans to write complex programs, as they can focus on expressing their ideas in a way that makes sense rather than worrying about the specific details of how the computer will interpret and execute their code.
During the compilation process, the compiler checks the syntax and semantics of the source code to ensure that it conforms to the rules of the programming language. If there are any errors or warnings, the compiler will report them to the programmer.
Once the code has been successfully compiled, the resulting machine code can be executed on a computer. This makes the compiler an essential tool for software development, as it allows programmers to write code in a high-level programming language and then transform it into machine code that can run on a variety of hardware platforms.
Flow of Transformation
Now you know what a translator is, let’s get into what a Language Processor is. Language processors are essential tools in the software development process. They allow programmers to write code in a high-level language, which is easier to read and understand, and then translate it into machine code that can be executed by a computer. This simplifies the development process and makes it easier to write complex programs. Now, several other programs may also be required for the computer to execute the code you have written. For example, how will the compiler know what a printf statement does. For that, we use the C’s inbuilt stdio.h (Standard Input Output Library), which defines printf statement and how it is executed. So while compiling, we need to make sure that these are also linked into the source code. This task of collecting source code is done by the Language Processor.
Preprocessor
The first stage the code goes through is to the Preprocessor. A preprocessor is a tool that processes the source code before it is compiled, and performs certain operations on it to prepare it for compilation. The preprocessor is a separate program that is run before the compiler itself. It also expands macros into the source language statements. Macros are a type of preprocessor directive that allows programmers to define a sequence of code that can be reused multiple times throughout a program. Macros are essentially a way to automate the process of writing code by allowing the programmer to define a shorthand notation for commonly used code sequences. There are some preprocessors that has the capability to remove comments as well, but usually this is done at the Lexical Analysis stage of the Compiler.
// Example of Macros
// Defines Marcro "MAX" which calculated the highest value
#define MAX(a, b) ((a) > (b) ? (a) : (b))
int x = 10, y = 20;
int max_val = MAX(x, y);This modified program is then fed to the compiler for further processing.
To avoid redundancy, I will not be writing about Compiler and Assembler here as it was already discussed earlier
Linker/Loader
A linker/loader is a program that combines multiple object files (compiled programs) into a single executable file that can be run on a computer.
A linker is a program that takes multiple object files and combines them into a single executable file or library. The linker resolves references between the object files, ensuring that all symbols are defined and linked correctly. It also performs various optimization tasks, such as removing unused code and data, and rearranging code and data for better performance.
A loader is a program that loads the executable file into memory and prepares it for execution. The loader reads the executable file from disk, maps it into memory, resolves any remaining external references, and sets up the initial program state. Once the loader has completed its tasks, control is transferred to the entry point of the program, and it begins executing.
In many modern systems, the linker and loader are combined into a single program, known as the linker/loader. This program performs both tasks, combining the object files into an executable and loading it into memory for execution.
The linker/loader is an important part of the compilation process, as it allows programmers to create complex programs consisting of multiple modules or libraries. Without the linker/loader, it would be much more difficult to build and distribute software on a large scale.
Phases of Compiler
Now the compilation process can be divided into two parts.
- Analysis (Front end)
- Synthesis (Back end)
Analysis
It is also known as front end of the compiler phase. It breaks up the source program into constituent pieces and imposes a grammatical structure onto them. It then uses this structure to create an intermediate representation of the source program. It also collects the information about the source program and stores it in a data structure called as the Symbol Table. It is passed along with the intermediate code to the Synthesis part.
Synthesis
It is also known as the back end of the compiler phase. It constructs the desired target program from the intermediate representation using the information from the Symbol Table. This part produces the Target Machine Code which is then Assembler.
Information: Several compiler phases may be grouped in some languages, and the compiler may not construct the intermediate representation explicitly. One common this that is seen while compiling is the use of symbol table in all phases of compilation.
Stages Of Compilation
The compilation process is a complex series of steps that a compiler goes through to convert source code written in one programming language into executable code. The exact stages and processes involved may vary depending on the type of compiler and the programming language being used. However, the general steps involved in the compilation process are as follows:
- Lexical Analysis
- Syntax Analysis
- Semantic Analysis
- Intermediate Code Generation
- Code Optimization
- Machine Code Generation
Each of these stages plays an important role in transforming the source code into executable code that can be executed on a computer.
Lexical Analysis:
The first step in the compilation process is lexical analysis, which involves breaking the source code into a sequence of tokens. Tokens are the basic building blocks of a programming language, and they represent keywords, identifiers, operators, and other elements of the code. The lexical analyzer, also known as a scanner, reads the source code character by character and groups them into tokens. The output of this stage is a stream of tokens that will be used in the next stage. To know more about Lexical Analysis, visit by blog “Breaking Down Words: The Art of Lexical Analysis in Compiler Design”.
Syntax Analysis:
After lexical analysis, the next step is syntax analysis, also called parsing. In this stage, the compiler checks whether the sequence of tokens generated in the previous stage conforms to the grammar of the programming language being used. The grammar of a programming language is a set of rules that define how the language’s elements can be combined to form valid statements. If the sequence of tokens does not match the grammar, the parser will report an error. If there are no errors, the parser will create a parse tree, which is a hierarchical representation of the code’s syntactic structure. During syntax analysis, the compiler generates a parse tree or abstract syntax tree (AST) that represents the syntactic structure of the code.
Semantic Analysis:
The third stage is semantic analysis. In this stage, the compiler checks whether the parse tree generated in the previous stage conforms to the semantic rules of the programming language. The semantic rules define how the language’s elements should be used and how they relate to each other. The semantic analyzer checks for errors such as type mismatches, undeclared variables, and incorrect function calls. The output of this stage is an annotated parse tree that includes additional information about the code’s meaning.
Intermediate Code Generation:
After semantic analysis, the next stage is intermediate code generation. In this stage, the compiler generates an intermediate representation of the code that is independent of the target machine architecture. The purpose of this stage is to simplify the code and make it easier to optimize. The intermediate code can be in various forms, such as a three-address code, a stack-based code, or a bytecode.
Optimization:
The next stage is optimization. In this stage, the compiler applies various optimization techniques to the intermediate code to improve its performance. Optimization can involve techniques such as constant folding, loop unrolling, and function inlining. The goal of optimization is to produce code that runs faster and uses fewer resources.
Code Generation:
The final stage is code generation. In this stage, the compiler generates machine code that can be executed on the target hardware platform. The machine code can be in various forms, such as assembly language, object code, or executable code. The code generator takes the optimized intermediate code as input and translates it into machine code. The output of this stage is an executable program that can be run on the target machine.
