[turbofan] Load elimination - use maps to avoid state invalidation.
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}
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