sensitivity-problem.js

function ParallelArray(buf) {
  this.buffer = buf;
}

ParallelArray.prototype.get = function (i) {
IC1:  var v = this.buffer[i];
  return v;
}

function MakeOrGetWrapperFromKey(f) {
  // compute start and end somehow
  return %Clone(f, function (buffer) { // pretend f is the key
    for (var i = start; i < end; i++) {
IC2:     buffer[i] = f(i);
    }
  });
}

ParallelArray.prototype.map = function (f) {
  var newBuffer = %NewTypeKeyedToScriptPC([]);
  var kernelWrapper = MakeOrGetWrapperFromKey(f);
  return new ParallelArray(%Fill(newBuffer, kernelWrapper));
}

var pa = new ParallelArray([1,2,3]);
// these create new clones, so there will be 2 copies of IC2, each will be specialized to the buffer as it sees it in this execution
var pa2 = pa.map(function f(x) { return x+1; });
var pa3 = pa2.map(function f(x) { return x-1; });
// these all access the same get function, so there's only one copy of IC1 to record all the types of the buffers seen. it eventually overflows and deopts.
pa.get(0);
pa2.get(0);
pa3.get(0);