js/src/jit-test/tests/gc/pretenuring.js


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// Test nursery string allocation and pretenuring.

gczeal(0);

gcparam("minNurseryBytes", 4096 * 1024);
gcparam("maxNurseryBytes", 4096 * 1024);
gc();

// String allocation in the nursery is initially enabled.
assertEq(nurseryStringsEnabled(), true);

// Literal strings are atoms (which are always tenured).
assertEq(isNurseryAllocated("foo"), false);

// The result of Number.toString is nursery allocated.
assertEq(isNurseryAllocated((1234).toString()), true);

// Ropes are nursery allocated.
let s = "bar";
assertEq(isNurseryAllocated("foo" + s), true);

// Dependent strings are nursery allocated.
assertEq(isNurseryAllocated("foobar".substr(1)), true);

// The testing function 'newString' allows control over which heap is used.
assertEq(isNurseryAllocated(newString("foobar", { tenured: true })), false);
assertEq(isNurseryAllocated(newString("foobar", { tenured: false })), true);

// Allocating lots of strings which survive nursery collection disables
// allocating strings in the nursery.
let a = [];
for (let i = 1; i < 500000; i++) {
  a.push(i.toString());
}
gc();
assertEq(nurseryStringsEnabled(), false);

// When a large number of strings are collected by major GC nursery allocation
// is enabled again.
a = undefined;
gc();
assertEq(nurseryStringsEnabled(), true);