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Architecture

crates/oxc_minifier/docs/ARCHITECTURE.md

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Architecture

Design Philosophy

Achieve maximum compression through comprehensive optimizations while maintaining correctness.

Size Optimization Strategy

  • Fixed-point iteration until no more improvements
  • Combine multiple optimization techniques
  • Learn from all major minifiers
  • Apply optimizations exhaustively

Learning from Industry Leaders

From Closure Compiler (Size Focus)

  • Advanced dead code elimination
  • Aggressive constant folding
  • Cross-statement optimizations
  • Property flattening techniques
  • Whole program analysis

From Terser/UglifyJS (Comprehensive)

  • All peephole optimizations
  • Battle-tested patterns
  • Edge case handling
  • Extensive transformation catalog

From esbuild (Performance)

  • Minimal AST passes where possible
  • Arena allocation strategy
  • Efficient algorithms
  • Smart traversal patterns

From SWC (Modern)

  • Rust safety and performance
  • Clean visitor pattern
  • Parallel processing potential
  • Modern architecture

Core Components

Compressor (compressor.rs)

Orchestrates the optimization pipeline with fixed-point iteration.

rust
pub struct Compressor<'a> {
    allocator: &'a Allocator,
}

Key responsibilities:

  • Builds semantic model
  • Applies normalization
  • Runs peephole optimizations to fixed-point
  • Manages optimization state

Peephole Optimizations (peephole/)

17+ transformation passes including:

  • Constant folding
  • Dead code elimination
  • Control flow optimization
  • Expression simplification
  • Syntax substitution

Each optimization implements transformations in the AST traversal visitor pattern.

Context (ctx.rs)

Shared utilities for optimizations:

  • AST manipulation helpers
  • Constant evaluation
  • Side effect analysis
  • Semantic utilities
rust
pub struct Ctx<'a, 'b> {
    // Provides access to:
    // - AST builder
    // - Scoping information
    // - Symbol values
    // - Optimization options
}

State Management (state.rs)

Tracks optimization state:

  • Symbol values
  • Changed flags
  • Pure functions
  • Source type

Optimization Pipeline

1. Parse and Build Semantic Model
   └─> SemanticBuilder creates scoping and symbols

2. Normalization Pass
   └─> Convert to canonical form for optimizations

3. Peephole Optimization Loop
   └─> Apply all optimizations
   └─> Check if any changes made
   └─> Repeat until fixed-point (no changes)

4. Optional Mangling
   └─> Rename variables for size

5. Code Generation
   └─> Output optimized JavaScript

Memory Management

  • Arena allocation via oxc_allocator
  • Minimal cloning through TakeIn trait
  • Efficient AST manipulation with arena pointers

Traversal Strategy

Using oxc_traverse for AST walking:

  • Enter/exit hooks for each node type
  • Bottom-up transformations (exit handlers)
  • State tracking through context

Integration Points

  • oxc_ast: AST node definitions
  • oxc_semantic: Scope and symbol analysis
  • oxc_ecmascript: ECMAScript operations
  • oxc_mangler: Variable renaming
  • oxc_codegen: Output generation