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diff --git a/js/src/jit-test/tests/wasm/memory-control/memory-discard.js b/js/src/jit-test/tests/wasm/memory-control/memory-discard.js
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+++ b/js/src/jit-test/tests/wasm/memory-control/memory-discard.js
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+// |jit-test| skip-if: !wasmMemoryControlEnabled(); test-also=--wasm-memory64; test-also=--no-wasm-memory64
+
+// This tests memory.discard and WebAssembly.Memory.discard() by placing data
+// (the alphabet) halfway across a page boundary, then discarding the first
+// page. The first half of the alphabet should be zeroed; the second should
+// not. The memory should remain readable and writable.
+//
+// The ultimate goal is to release physical pages of memory back to the
+// operating system, but we can't really observe memory metrics here. Oh well.
+
+function initModule(discardOffset, discardLen, discardViaJS, shared, memType = 'i32') {
+    const memProps = shared ? '4 4 shared' : '4'; // 4 pages
+    const text = `(module
+        (memory (export "memory") ${memType} ${memProps})
+        (data "abcdefghijklmnopqrstuvwxyz")
+        (func (export "init")
+            ;; splat alphabet halfway across the 3/4 page boundary.
+            ;; 196595 = (65536 * 3) - (26 / 2)
+            (memory.init 0 (${memType}.const 196595) (i32.const 0) (i32.const 26))
+        )
+        (func (export "letter") (param i32) (result i32)
+            (i32.load8_u (${memType}.add (${memType}.const 196595) ${memType == 'i64' ? '(i64.extend_i32_u (local.get 0))' : '(local.get 0)'}))
+        )
+        (func (export "discard")
+            (memory.discard (${memType}.const ${discardOffset}) (${memType}.const ${discardLen}))
+        )
+    )`;
+    const exp = wasmEvalText(text).exports;
+
+    return [exp, discardViaJS ? () => exp.memory.discard(discardOffset, discardLen) : exp.discard];
+}
+
+function checkRegion(exp, min, max, expectLetters) {
+    for (let i = min; i < max; i++) {
+        const c = "a".charCodeAt(0) + i;
+        const expected = expectLetters ? c : 0;
+        assertEq(exp.letter(i), expected, `checking position of letter ${String.fromCharCode(c)}`);
+    }
+}
+function checkFirstHalf(exp, expectLetters) { return checkRegion(exp, 0, 13, expectLetters) }
+function checkSecondHalf(exp, expectLetters) { return checkRegion(exp, 13, 26, expectLetters) }
+function checkWholeAlphabet(exp, expectLetters) { return checkRegion(exp, 0, 26, expectLetters) }
+
+function testAll(func) {
+    func(false, false, 'i32');
+    func(false, true, 'i32');
+    func(true, false, 'i32');
+    func(true, true, 'i32');
+    if (wasmMemory64Enabled()) {
+        func(false, false, 'i64');
+        func(false, true, 'i64');
+        func(true, false, 'i64');
+        func(true, true, 'i64');
+    }
+}
+
+testAll(function testHappyPath(discardViaJS, shared, memType) {
+    // Only page 3 of memory, half the alphabet
+    const [exp, discard] = initModule(65536 * 2, 65536, discardViaJS, shared, memType);
+
+    // All zero to start
+    checkWholeAlphabet(exp, false);
+
+    // Then all alphabet
+    exp.init();
+    checkWholeAlphabet(exp, true);
+
+    // Discarding the first page clears the first half of the alphabet
+    discard();
+    checkFirstHalf(exp, false);
+    checkSecondHalf(exp, true);
+
+    // We should be able to write back to a discarded region of memory
+    exp.init();
+    checkWholeAlphabet(exp, true);
+
+    // ...and then discard again
+    discard();
+    checkFirstHalf(exp, false);
+    checkSecondHalf(exp, true);
+});
+
+testAll(function testZeroLen(discardViaJS, shared) {
+    // Discard zero bytes
+    const [exp, discard] = initModule(PageSizeInBytes * 2, 0, discardViaJS, shared);
+
+    // Init the stuff
+    exp.init();
+    checkWholeAlphabet(exp, true);
+
+    // Discarding zero bytes should be valid...
+    discard();
+
+    // ...but should have no effect.
+    checkWholeAlphabet(exp, true);
+});
+
+testAll(function testWithGrow(discardViaJS, shared, memType) {
+    if (shared) {
+        return; // shared memories cannot grow
+    }
+
+    // Only page 3 of memory, half the alphabet. There is no max size on the
+    // memory, so it will be subject to moving grows in 32-bit mode.
+    const [exp, discard] = initModule(65536 * 2, 65536, discardViaJS, false, memType);
+
+    // Start with the whole alphabet
+    exp.init();
+    checkWholeAlphabet(exp, true);
+
+    // Discarding the first page clears the first half of the alphabet
+    discard();
+    checkFirstHalf(exp, false);
+    checkSecondHalf(exp, true);
+
+    // Oops we just grew by a preposterous amount, time to move
+    exp.memory.grow(200)
+
+    // The memory should still be readable
+    checkFirstHalf(exp, false);
+    checkSecondHalf(exp, true);
+
+    // We should be able to write back to a discarded region of memory
+    exp.init();
+    checkWholeAlphabet(exp, true);
+
+    // ...and then discard again
+    discard();
+    checkFirstHalf(exp, false);
+    checkSecondHalf(exp, true);
+});
+
+testAll(function testOOB(discardViaJS, shared) {
+    // Discard two pages where there is only one
+    const [exp, discard] = initModule(PageSizeInBytes * 3, PageSizeInBytes * 2, discardViaJS, shared);
+
+    exp.init();
+    checkWholeAlphabet(exp, true);
+    assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /out of bounds/);
+
+    // Ensure nothing was discarded
+    checkWholeAlphabet(exp, true);
+});
+
+testAll(function testOOB2(discardViaJS, shared) {
+    // Discard two pages starting near the end of 32-bit address space
+    // (would trigger an overflow in 32-bit world)
+    const [exp, discard] = initModule(2 ** 32 - PageSizeInBytes, PageSizeInBytes * 2, discardViaJS, shared);
+
+    exp.init();
+    checkWholeAlphabet(exp, true);
+    assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /out of bounds/);
+
+    // Ensure nothing was discarded
+    checkWholeAlphabet(exp, true);
+});
+
+testAll(function testOOB3(discardViaJS, shared) {
+    // Discard nearly an entire 32-bit address space's worth of pages. Very exciting!
+    const [exp, discard] = initModule(0, 2 ** 32 - PageSizeInBytes, discardViaJS, shared);
+
+    exp.init();
+    checkWholeAlphabet(exp, true);
+    assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /out of bounds/);
+
+    // Ensure nothing was discarded
+    checkWholeAlphabet(exp, true);
+});
+
+(function testOOB4() {
+    // Discard an entire 32-bit address space's worth of pages. JS can do this
+    // even to 32-bit memories because it can handle numbers bigger
+    // than 2^32 - 1.
+    const [exp, _] = initModule(0, 0, false); // pass zero to allow the wasm module to validate
+    const discard = () => exp.memory.discard(0, 2 ** 32);
+
+    exp.init();
+    checkWholeAlphabet(exp, true);
+    assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /out of bounds/);
+
+    // Ensure nothing was discarded
+    checkWholeAlphabet(exp, true);
+})();
+
+if (wasmMemory64Enabled()) {
+    (function testOverflow() {
+        // Discard UINT64_MAX - (2 pages), starting from page 4. This overflows but puts both start and end in bounds.
+        // This cannot be done with a JS discard because JS can't actually represent big enough integers.
+
+        // The big ol' number here is 2^64 - (65536 * 2)
+        const [exp, discard] = initModule(65536 * 3, `18_446_744_073_709_420_544`, false, false, 'i64');
+
+        // Init the stuff
+        exp.init();
+        checkWholeAlphabet(exp, true);
+
+        // Discarding should not be valid when it goes out of bounds
+        assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /out of bounds/);
+
+        // Ensure nothing was discarded
+        checkWholeAlphabet(exp, true);
+    })();
+}
+
+testAll(function testMisalignedStart(discardViaJS, shared) {
+    // Discard only the first half of the alphabet (this misaligns the start)
+    const [exp, discard] = initModule(PageSizeInBytes * 3 - 13, 13, discardViaJS, shared);
+
+    exp.init();
+    checkWholeAlphabet(exp, true);
+    assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /unaligned/);
+
+    // Ensure nothing was discarded
+    checkWholeAlphabet(exp, true);
+});
+
+testAll(function testMisalignedEnd(discardViaJS, shared) {
+    // Discard only the second half of the alphabet (this misaligns the end)
+    const [exp, discard] = initModule(PageSizeInBytes * 3, 13, discardViaJS, shared);
+
+    exp.init();
+    checkWholeAlphabet(exp, true);
+    assertErrorMessage(() => discard(), WebAssembly.RuntimeError, /unaligned/);
+
+    // Ensure nothing was discarded
+    checkWholeAlphabet(exp, true);
+});