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    • Jaroslav Sevcik's avatar
      [turbofan] Optimize array destructuring · 3fe7d698
      Jaroslav Sevcik authored
      This CL introduces type narrowing and constant folding reducers
      to constant fold code that comes out of inlined destructuring
      of arrays. In particular, array iterator introduces code that
      contains a phi of a temporary array that blocks escape analysis.
      The phi comes from conditional that can be evaluated statically
      (i.e., constant folded), so with better constant folding we
      allow escape analysis to get rid of the temporary array.
      
      On a quick micro-benchmark below, we see more than 6x improvement.
      This is close to the hand-optimized version - if we replace
      body of f with 'return b + a', we get 220ms (versus 218ms with
      destructuring).
      
      function f(a, b) {
        [b, a] = [a, b];
        return a + b;
      }
      
      function sum(count) {
        let s = 0;
        for (let i = 0; i < count; i++) {
          s += f(1, 2);
        }
        return s;
      }
      
      // Warm up
      sum(1e5); sum(1e5);
      console.time("destructure array");
      sum(1e8);
      console.timeEnd("destructure array");
      
      console.timeEnd: destructure array, 213.526000
      
      console.timeEnd: destructure array, 1503.537000
      
      Bug: v8:7728
      Change-Id: Ib7aec1d5897989e6adb1af1eddd516d8b3866db5
      Reviewed-on: https://chromium-review.googlesource.com/1047672Reviewed-by: 's avatarBenedikt Meurer <bmeurer@chromium.org>
      Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
      Cr-Commit-Position: refs/heads/master@{#53048}
      3fe7d698