v8/test/mjsunit/regress/regress-fast-literal-transition.js

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// Flags: --allow-natives-syntax --always-opt --expose-gc

// Test that the elements kind of the boilerplate object is sufficiently
// checked in LFastLiteral, so that unoptimized code can transition the
// boilerplate. The --always-opt flag makes sure that optimized code is
// not thrown away at deoptimization.

// The switch statement in f() makes sure that f() is not inlined. If we
// start inlining switch statements, we will still catch the bug on the
// final --stress-opt run.

function f(x) {
  switch (x) {
    case 1:
      return 1.4;
    case 2:
      return 1.5;
    case 3:
      return {};
    default:
      gc();
  }
}

function g(x) {
  return [1.1, 1.2, 1.3, f(x)];
}

// Step 1: Optimize g() to contain a PACKED_DOUBLE_ELEMENTS boilerplate.
;
%PrepareFunctionForOptimization(g);
assertEquals([1.1, 1.2, 1.3, 1.4], g(1));
assertEquals([1.1, 1.2, 1.3, 1.5], g(2));
%OptimizeFunctionOnNextCall(g);

// Step 2: Deoptimize g() and transition to PACKED_ELEMENTS boilerplate.
assertEquals([1.1, 1.2, 1.3, {}], g(3));

// Step 3: Cause a GC while broken clone of boilerplate is on the heap,
// hence causing heap verification to catch it.
assertEquals([1.1, 1.2, 1.3, undefined], g(4));