Bootstrapping in Compiler Development: Creating Self-Hosting Compilers

Explore bootstrapping, a crucial technique in compiler development used to create self-hosting compilers. This guide explains the process of creating a compiler that can compile its own source code, its importance in language evolution, and the iterative steps involved in bootstrapping a new compiler.

Bootstrapping in Compiler Development

What is Bootstrapping?

Bootstrapping is a technique used to create a self-hosting compiler—a compiler that can compile its own source code. This is essential because it allows compilers to evolve and generate new, improved versions of themselves without needing to use a compiler written in a different language. It also allows a compiler written in a new programming language to be created without needing to use a compiler that already supports that language. The process typically involves creating a simpler version of the compiler first and then using that simpler compiler to compile a more advanced version. This process is repeated to create a fully functional and self-hosting compiler.

Understanding Self-Hosting Compilers

A self-hosting compiler is written in the same language it compiles. Once created, it can recompile itself, making it independent and capable of generating new versions without external tools. This is especially useful for creating compilers for new programming languages, as it avoids needing a pre-existing compiler for that language.

Compiler Characteristics

To understand bootstrapping, we need to consider the languages involved in a compiler:

  • Source Language (S): The language the compiler translates.
  • Target Language (T): The language the compiler produces.
  • Implementation Language (I): The language the compiler is written in.

A compiler can be represented as S CI T (Source language S, compiled using a compiler written in language I, to produce target code T).

Steps in Bootstrapping a Compiler

To create a new compiler for a new language L that runs on machine A:

  1. Create a Subset Compiler: Develop a simpler compiler (S CA A) for a subset of L, using language A (the target machine's language). This compiler needs to run on machine A.
  2. Create a Full Compiler: Create a full compiler (L CS A) written in the subset language S of L. This is a more complete version of the compiler, able to compile the full language L.
  3. Compile the Full Compiler: Compile the full compiler (L CS A) using the subset compiler (S CA A) This produces the final compiler (L CA A), which runs on machine A and compiles the full language L.

This entire process is known as bootstrapping. It’s iterative and allows a compiler to evolve from a simpler version to a fully functional, self-hosting version.

Importance of Bootstrapping

Bootstrapping is crucial for compiler development because:

  • It allows creating compilers for new languages without needing a pre-existing compiler for that language.
  • It enables compiler evolution and improvement; new features and optimizations can be added over time.