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diff --git a/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs b/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs
new file mode 100644
index 000000000..391daed20
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+++ b/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs
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+use crate::sync::atomic::Ordering;
+
+#[cfg(test)]
+use stdarch_test::assert_instr;
+
+/// Compares and exchange 16 bytes (128 bits) of data atomically.
+///
+/// This intrinsic corresponds to the `cmpxchg16b` instruction on `x86_64`
+/// processors. It performs an atomic compare-and-swap, updating the `ptr`
+/// memory location to `val` if the current value in memory equals `old`.
+///
+/// # Return value
+///
+/// This function returns the previous value at the memory location. If it is
+/// equal to `old` then the memory was updated to `new`.
+///
+/// # Memory Orderings
+///
+/// This atomic operations has the same semantics of memory orderings as
+/// `AtomicUsize::compare_exchange` does, only operating on 16 bytes of memory
+/// instead of just a pointer.
+///
+/// For more information on memory orderings here see the `compare_exchange`
+/// documentation for other `Atomic*` types in the standard library.
+///
+/// # Unsafety
+///
+/// This method is unsafe because it takes a raw pointer and will attempt to
+/// read and possibly write the memory at the pointer. The pointer must also be
+/// aligned on a 16-byte boundary.
+///
+/// This method also requires the `cmpxchg16b` CPU feature to be available at
+/// runtime to work correctly. If the CPU running the binary does not actually
+/// support `cmpxchg16b` and the program enters an execution path that
+/// eventually would reach this function the behavior is undefined.
+///
+/// The `success` ordering must also be stronger or equal to `failure`, or this
+/// function call is undefined. See the `Atomic*` documentation's
+/// `compare_exchange` function for more information. When `compare_exchange`
+/// panics, this is undefined behavior. Currently this function aborts the
+/// process with an undefined instruction.
+#[inline]
+#[cfg_attr(test, assert_instr(cmpxchg16b, success = Ordering::SeqCst, failure = Ordering::SeqCst))]
+#[target_feature(enable = "cmpxchg16b")]
+pub unsafe fn cmpxchg16b(
+    dst: *mut u128,
+    old: u128,
+    new: u128,
+    success: Ordering,
+    failure: Ordering,
+) -> u128 {
+    use crate::{intrinsics, sync::atomic::Ordering::*};
+
+    debug_assert!(dst as usize % 16 == 0);
+
+    let (val, _ok) = match (success, failure) {
+        (Acquire, Acquire) => intrinsics::atomic_cxchg_acq(dst, old, new),
+        (Release, Relaxed) => intrinsics::atomic_cxchg_rel(dst, old, new),
+        (AcqRel, Acquire) => intrinsics::atomic_cxchg_acqrel(dst, old, new),
+        (Relaxed, Relaxed) => intrinsics::atomic_cxchg_relaxed(dst, old, new),
+        (SeqCst, SeqCst) => intrinsics::atomic_cxchg(dst, old, new),
+        (Acquire, Relaxed) => intrinsics::atomic_cxchg_acq_failrelaxed(dst, old, new),
+        (AcqRel, Relaxed) => intrinsics::atomic_cxchg_acqrel_failrelaxed(dst, old, new),
+        (SeqCst, Relaxed) => intrinsics::atomic_cxchg_failrelaxed(dst, old, new),
+        (SeqCst, Acquire) => intrinsics::atomic_cxchg_failacq(dst, old, new),
+
+        // The above block is all copied from libcore, and this statement is
+        // also copied from libcore except that it's a panic in libcore and we
+        // have a little bit more of a lightweight panic here.
+        _ => crate::core_arch::x86::ud2(),
+    };
+    val
+}