WebAssembly (Wasm) Optimizer Skill

This skill provides guidelines and tools for optimizing WebAssembly modules used in the project, particularly for game engine adapters (e.g., Stockfish).

Capabilities

1. •Size Optimization: Strategies to minimize .wasm binary size (e.g., using wasm-opt, compiler flags).
2. •Loading Performance: Best practices for fetching, compiling, and instantiating Wasm modules (streaming compilation).
3. •Memory Management: Guidelines for managing Wasm memory from JavaScript/TypeScript to prevent leaks.
4. •Integration: Patterns for seamless communication between Wasm and the main JS thread or Web Workers.

Optimization Checklist

• • Compiler Flags: Are you using optimization flags like -O3, -Oz, or -Os?
• • Binary Stripping: Have debug symbols been stripped from the production binary?
• • wasm-opt: Is the binary post-processed with wasm-opt (from Binaryen)?
• • Streaming Compilation: Do you use WebAssembly.instantiateStreaming where supported?
• • Compression: Is the .wasm file served with Brotli or Gzip compression?

Code Snippets

Efficient Instantiation

// Prefer instantiateStreaming for better performance
async function loadWasm(url: string, importObject: WebAssembly.Imports) {
  if (WebAssembly.instantiateStreaming) {
    return await WebAssembly.instantiateStreaming(fetch(url), importObject);
  } else {
    const response = await fetch(url);
    const bytes = await response.arrayBuffer();
    return await WebAssembly.instantiate(bytes, importObject);
  }
}

Tools

• •Emscripten: Standard SDK for compiling C/C++ to Wasm.
• •Binaryen (wasm-opt): Compiler infrastructure and optimization toolchain.
• •Twiggy: A code size profiler for Wasm.
• •wasm-snip: Replaces unneeded Wasm functions with unreachable.

Troubleshooting

• •"Out of bounds memory access": Check for correct pointer arithmetic and memory allocation sizes on the JS side.
• •"LinkError: Import #x module="env" function="...": function import requires a callable": Verify that the importObject passed to instantiation matches the imports expected by the Wasm module.