How Does Code Transform Into Machine Instructions? A Step‑by‑Step Compiler Guide

Programs you write are just text strings; a compiler converts that text into binary instructions the CPU can execute. The process begins with a button in an IDE that triggers the compilation pipeline.

Tokenization

The compiler first scans the source string, discarding whitespace and line breaks, and groups characters into meaningful units called tokens (e.g., keywords like int and main, literals like 0 and 5).

Parsing and AST Construction

Next, the compiler parses the token stream according to the language grammar. For example, when it encounters an if token, it applies the if -statement grammar, building a hierarchical representation called an Abstract Syntax Tree (AST). The AST shows the structure: the if keyword, opening parenthesis, boolean expression, closing parenthesis, and the statement block.

Code Generation

The compiler then traverses the AST to emit instructions. In a simple example it may generate assembly that directly reflects the source logic.

Real compilers often do not emit final machine code at this stage; they produce intermediate representations that later back‑ends translate for specific CPU architectures (e.g., x86 vs. ARM).

Target‑Specific Back‑Ends and LLVM

If you design a new language, you must write a back‑end for each target architecture. LLVM solves this by providing a common intermediate language; the compiler emits LLVM IR, and LLVM handles the rest, generating optimized machine code for the chosen CPU.

Optimization

During code generation the compiler performs optimizations, such as removing dead code. In the example, an unused variable a is eliminated, so its assignment instruction disappears from the final output.

Object Files and Linking

Each compiled source file becomes an object file containing the binary instructions. A linker then combines all object files, resolves symbols, and produces the final executable program.

The article originally included a call to follow a public account for more linker details, but the technical explanation above stands on its own.