b342cbb20b
This reverts commit b8f9166664.
Reason for revert: Fails gc-stress (https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20gc%20stress/28341).
Original change's description:
> [flags] warn about contradictory flags
>
> Design Doc: https://docs.google.com/document/d/1lkvu8crkK7Ei39qjkPCFijpNyxWXsOktG9GB-7K34jM/
>
> Bug: v8:10577
> Change-Id: Ib9cfdffa401c48c895bf31caed5ee03545beddab
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154792
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Reviewed-by: Tamer Tas <tmrts@chromium.org>
> Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#68168}
TBR=machenbach@chromium.org,neis@chromium.org,clemensb@chromium.org,tebbi@chromium.org,tmrts@chromium.org
Change-Id: Ia1e3373fbb4c369594ceb98eb560e3ccf2cb8780
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10577
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2230523
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68169}
70 lines
2.7 KiB
JavaScript
70 lines
2.7 KiB
JavaScript
// Copyright 2015 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Flags: --random-seed=20 --nostress-opt --noalways-opt --predictable
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(function() {
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var kHistory = 2;
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var kRepeats = 100;
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var history = new Uint32Array(kHistory);
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function random() {
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return (Math.random() * Math.pow(2, 32)) >>> 0;
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}
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function ChiSquared(m, n) {
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var ys_minus_np1 = (m - n / 2.0);
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var chi_squared_1 = ys_minus_np1 * ys_minus_np1 * 2.0 / n;
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var ys_minus_np2 = ((n - m) - n / 2.0);
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var chi_squared_2 = ys_minus_np2 * ys_minus_np2 * 2.0 / n;
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return chi_squared_1 + chi_squared_2;
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}
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for (var predictor_bit = -2; predictor_bit < 32; predictor_bit++) {
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// The predicted bit is one of the bits from the PRNG.
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for (var random_bit = 0; random_bit < 32; random_bit++) {
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for (var ago = 0; ago < kHistory; ago++) {
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// We don't want to check whether each bit predicts itself.
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if (ago == 0 && predictor_bit == random_bit) continue;
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// Enter the new random value into the history
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for (var i = ago; i >= 0; i--) {
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history[i] = random();
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}
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// Find out how many of the bits are the same as the prediction bit.
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var m = 0;
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for (var i = 0; i < kRepeats; i++) {
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for (var j = ago - 1; j >= 0; j--) history[j + 1] = history[j];
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history[0] = random();
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var predicted;
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if (predictor_bit >= 0) {
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predicted = (history[ago] >> predictor_bit) & 1;
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} else {
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predicted = predictor_bit == -2 ? 0 : 1;
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}
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var bit = (history[0] >> random_bit) & 1;
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if (bit == predicted) m++;
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}
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// Chi squared analysis for k = 2 (2, states: same/not-same) and one
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// degree of freedom (k - 1).
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var chi_squared = ChiSquared(m, kRepeats);
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if (chi_squared > 24) {
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var percent = Math.floor(m * 100.0 / kRepeats);
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if (predictor_bit < 0) {
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var bit_value = predictor_bit == -2 ? 0 : 1;
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print(`Bit ${random_bit} is ${bit_value} ${percent}% of the time`);
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} else {
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print(`Bit ${random_bit} is the same as bit ${predictor_bit} ` +
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`${ago} ago ${percent}% of the time`);
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}
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}
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// For 1 degree of freedom this corresponds to 1 in a million. We are
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// running ~8000 tests, so that would be surprising.
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assertTrue(chi_squared <= 24);
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// If the predictor bit is a fixed 0 or 1 then it makes no sense to
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// repeat the test with a different age.
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if (predictor_bit < 0) break;
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}
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}
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}
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})();
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