Recover Instructions

1. Optimizing JIT principles & Bailouts.
2. Current Optimizations.
3. Improving Bailouts with Recover Instructions.
4. Overview of Possible Optimizations.

        if (predicate() /* proved false */)
          /* remove code */
        …
      

Unreachable Code Elimination, remove unused branches.

        var failed = function (i) {
          if (i > 9997)
            failed = function (i) { return true; } 
          return false; 
        }
      

          if (failed(i) || failed(i))
            /* Inlining → Removed by UCE */
      

Cause invalidation on scripts inlining this function.

        function ra(i) {
          var x = (-1 >> 1) + 308641 * i;
          //  ^ Computed with int32s.
          failed(i); failed(i);
          
          print(x | 0);
        }
      

        function ra(i) {
          var x = (-1 >> 1) + 308641 * i;
          //  ^ Computed with doubles.
          if (failed(i) || failed(i))
            return; /* print(x); */
          print(x | 0);
        }
      

UCE prevents Range Analysis optimizations.

Removing writes is just about adding write instructions to the list of recover instructions.

→ Implies precise alias analysis.

→ Needed Escape analysis.