Wasm Optimizer

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.

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