Currently, the transition elements kind operation invalidates the
elements of all other arrays. In particular, if we loop over matrix 
elements using two nested loops, and do possibly transitioning access 
a[i][j] in every iteration, we invalidate the load elimination state 
for the array 'a' because a[i][j] might transition elements kind 
for the 'a[i]' array. As a result, the 'a[i]' access cannot be 
hoisted from the inner loop.

With this CL, we figure out that transitioning 'a[i]' cannot affect 'a'
because we know that 'a' does not have the transition's source map.

In the micro-benchmark below, the time for summing up the elements of
100x100 matrix improves by factor of 1.7 (from ~340ms to ~190ms).

function matrixSum(a) {
  let s = 0;
  let rowCount = a.length;
  let columnCount = a[0].length;
  for (let i = 0; i < rowCount; i++) {
    for (let j = 0; j < columnCount ; j++) {
      s += a[i][j];
    }
  }
  return s;
}

// Setup the matrices:
// Smi elements.
var ma = [[1, 2], [3, 4]];
// Holey double elements.
var b = Array(100);
for (let i = 0; i < 100; i++) b[i] = 1.1;
var mb = [];
for (let i = 0; i < 100; i++) mb[i] = b;

// Warmup.
matrixSum(mb);
matrixSum(mb);
matrixSum(ma);
matrixSum(mb);
matrixSum(ma);

%OptimizeFunctionOnNextCall(matrixSum);

function runner(m) {
  let s = 0;
  for (let i = 0; i < 1e4; i++) {
    s += matrixSum(m);
  }
  return s;
}
// Make sure the runner does not know the elements kinds.
%NeverOptimizeFunction(runner);

// Measure.
console.time("Sum");
runner(mb);
console.timeEnd("Sum");


Bug: v8:6344
Change-Id: Ie0642d8693ed63116b1aaed7d2f261fcb64729fe
Reviewed-on: https://chromium-review.googlesource.com/704634
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48334}