v8/test/mjsunit/regress/regress-2250.js

// Copyright 2012 the V8 project authors. All rights reserved.
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// Flags: --allow-natives-syntax --opt

// The original problem from the bug: In the example below SMI check for b
// generated for inlining of equals invocation (marked with (*)) will be hoisted
// out of the loop across the typeof b === "object" condition and cause an
// immediate deopt. Another problem here is that no matter how many time we
// deopt and reopt we will continue to produce the wrong code.
//
// The fix is to notice when a deopt and subsequent reopt doesn't find
// additional type information, indicating that optimistic LICM should be
// disabled during compilation.

function eq(a, b) {
  if (typeof b === "object") {
    return b.equals(a);  // (*)
  }
  return a === b;
}

Object.prototype.equals = function (other) {
  return (this === other);
};

function test() {
  for (var i = 0; !eq(i, 10); i++)
    ;
}

%PrepareFunctionForOptimization(test);
eq({}, {});
eq({}, {});
eq(1, 1);
eq(1, 1);
test();
%OptimizeFunctionOnNextCall(test);
test();
%PrepareFunctionForOptimization(test);
%OptimizeFunctionOnNextCall(test);
// Second compilation should have noticed that LICM wasn't a good idea, and now
// function should no longer deopt when called.
test();
assertOptimized(test);