wiki:StateofJSC2016

The State of JSC

  • Moved from LLVM to B3/Air
    • Transition is complete
    • FTL Jit in 64-bit platforms
    • Big Jetstream improvements
    • Big Kraken improvements
  • Moved from Tracing to Sampling profiler
    • Performance is an order of magnitude better in Web Inspector
    • 10-20x faster with the sampling profiler
  • ES6 Feature Complete
    • Block Scoping
    • Generator Functions
  • Current work
    • ES6 Sample Bench
      • Fast Generators
      • Fast Map/Set
      • gotten 20% faster
      • Runs 2 different tests
      • Takes geometric mean of tests
      • Steady state
    • Concurrent Garbage Collection
      • Gonna mean pauses in JSC
      • Pauses won’t be nearly as long
      • Execute JS during GC
      • There will be points where you pause the world but it won’t be in high milliseconds
    • Working on WebAssembly
      • It’s being implemented
    • DOM JIT
      • Creating an abstraction for the JSC for operations on the DOM
      • Be aware of getter accessors of being compiled
    • Integrating ES6 Modules in HTML
      • <script type=“module”>
    • Almost done ES2017
      • Support everything buy async/await
      • Patches on async/await
  • Demo of command line:
    • ./Tools/Scripts/run-jsc —release —sample ~/test.js
    • Shows sampling rate
    • and the hottest byte code samples
    • The hash identifies the code blocks and just
    • These tools would be nice for WebContent process
      • Too difficult to use with the sample profiles
    • Would be cool to add byte code information in inspector
    • At a high level a Heat Map would be nice (being worked on)
    • If it is in inspector, it can impact performance and throw off the profile
    • JSC_dumpDFGDisassembly=1 ./Tools/Scripts/run-jsc —release —sample ~/test.js
  • How to async/await
    • async func with await is a shorthand for promises
    • await automatically wraps the given function in a Promise and returns the promise
  • WebAssembly
    • Work is underway
    • There is a trapping semantic in WebAssembly
    • Cant export a function that takes 64-bit integer
    • Internally in WebAssembly you can handle 64-bit integers
    • You have to check that the memory is in bounds, if not then you have to unwind the webassembly
    • Does the exception flatten the webassembly?
      • The plan is to have each WebAssembly frame visible
    • You can have import and export in WebAssembly to call from WebAssembly to JS
    • Developers would likely have WebAssembly that calls to a JS helper to modify DOM since you can’t modify the DOM from WebAssembly
    • There is a lot of debate still happening
    • You can use the JS GC for whatever language your using
    • How fast is WebAssembly?
      • Significantly faster for common cases of compiling C code
      • WASM is quite slow compared to native codes
      • WebAssembly has more info about how things work that allow for more optimizations
      • Close to native performance
    • How do I compile to WebAssembly?
      • Compile through clang, that pass it to LLVM IR then pass it back to WebAssembly
      • It will likely get easier as tools are created
Last modified 3 years ago Last modified on Oct 26, 2016 1:15:52 PM