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Introduction
We, programmers, write computer programs used to perform certain tasks in computers in high-level programming languages. But computers cannot understand these programs, so they need to be translated into machine-readable instructions. The compiler converts source code into machine code; single pass and multi pass compilers are two types of compilers.
In the following blog, we will learn about compilers. In detail, we will discuss two types of compilers, single pass and multi pass compilers. We will also read about the difference between a single pass and multi pass compiler for better understanding.
Single Pass Compiler
A source code goes through different stages during compilation. A single-pass compiler passes the code into these steps in a single-pass; in other words, it translates each part of the source code into the final required machine code.
Firstly, the compiler scans the source code during lexical analysisand divides it into similar tokens. Then, with the help of the Parse tree, it performs syntax analysis, verifying the code with the programming language's grammar. Finally, it generates the machine code. The three main steps are lexical analysis, syntax analysis, and code generation. There is no code optimization or intermediate code generation.
As not all programming languages are well-suited for single-pass compilation, here are some examples of programming languages related to single-pass compilers: Pascal, C, FORTRAN, etc.
Let's discuss some of the advantages of a single-pass compiler:
It is faster for small programs and embedded systems in case of small code size and critical time compilation.
It requires less memory.
It can generate the machine code faster than another type.
Disadvantages of Single Pass Compiler
Let's see some of the disadvantages of a single-pass compiler:
It cannot perform complex optimization techniques as we need to perform multiple passes for optimization.
There is no intermediate code generation.
It imposes some restrictions upon the program constants, variables, types, and procedures that must be defined before use.
Multi Pass Compiler
A multi-pass compiler makes the source code go through several passes during the compilation process; it also generates intermediate optimized code after each step. It converts the source program into one or more intermediate codes in steps between the source code and machine code. It reprocesses the entire program in each succeeding pass.
Each pass takes the result of the previous pass as the input and creates an intermediate optimized output. Likewise, the code improves in each pass until the final pass generates the required code. A multi-pass compiler performs additional tasks such as intermediate code generation, machine-dependent code optimization, and machine-independent code optimization.
Some examples of programming languages related to multi-pass compilers are Java, C++, Lisp, etc. These languages' codes are highly abstract and require multiple passes to optimize.
Advantages of Multi Pass Compiler
Let's discuss some of the advantages of a multi-pass compiler:
It is machine independent as multiple passes include a modular structure, and code generation is separate from other steps; the passes can be reused for different machines.
It works well with complex programming languages.
It generates better code than single-pass compilers, as they perform more optimization through multiple passes.
Disadvantages of Multi Pass Compiler
Let's also see some of the disadvantages of a multi-pass compiler:
It requires more memory and processing power as it goes through multiple passes over the source code and stores intermediate optimized codes.
It also increases the compilation time.
Difference Between Single Pass and Multi Pass Compiler
We have discussed single pass and multi pass compilers. Let's look at the difference between single pass and multi pass compilers for better understanding.
Single Pass
Multi Pass
Passes through each compilation step only once, instantly converting each token into the required machine code.
Passes the source code through the compilation process multiple times.
Faster than multi-pass compiler
It is comparatively slower as it goes through several passes and writes intermediate code in each pass.
It has a limited scope.
It has a greater scope.
It is also known as a narrow compiler.
It is also called a wide compiler.
There is no code optimization, and the code generation is less efficient.
Better code generation and optimization.
There is no intermediate code generation.
The intermediate code is generated during the process.
It takes less time to compile.
It takes more time to compile.
Some of the examples are Turbo Pascal and Small C compilers.
Some of the examples are LLVM and Java compilers. Also, Modula - 2 languages use it.
What is the difference between the single pass and multi pass compiler?
A single-pass compiler passes through the source code only once during compilation, translating each part into the final code at once. A multi-pass compiler compiles the source code in multiple passes.
What is an example single pass and multi pass compiler?
Some famous examples of single-pass compilers are Turbo Pascal, Small C compilers, etc. Examples of multi-pass compilers are GCC Compiler, Java Compiler, etc. There are many more examples, and the choice depends on your requirements.
Which stages are absent in single pass compilation?
The three main stages in a single pass compiler are lexical analysis, syntax analysis, and code generation. The optimization stage and intermediate code generation stage is not present in the single pass compiler.
Which is better single pass and multi pass compiler?
The choice between single pass and multi pass compilers depends on your needs. Single-pass compilers are simple and faster, making a good choice for small or simple projects. Multi-pass compilers are more efficient and powerful, a good choice for large or complex projects.
Conclusion
We hope this article was insightful and you learned something new. In this blog, we learned about types of compilers based on the number of passes. We learned about single pass and multi pass compilers. The choice between single pass and multi pass compilers depends on your requirements, such as the source code size, the level of optimization needed, etc. To help you make a good choice, we saw their advantages and disadvantages in the blog. In the end, we discussed the difference between single pass and multi pass compilers.
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