diff --git a/tests/compile-fail/weak_memory/imperfectly_overlapping.rs b/tests/compile-fail/weak_memory/imperfectly_overlapping.rs
deleted file mode 100644
index 6f91e147fa8..00000000000
--- a/tests/compile-fail/weak_memory/imperfectly_overlapping.rs
+++ /dev/null
@@ -1,35 +0,0 @@
-// ignore-windows: Concurrency on Windows is not supported yet.
-#![feature(atomic_from_mut)]
-#![feature(core_intrinsics)]
-
-use std::intrinsics::atomic_load;
-use std::sync::atomic::Ordering::*;
-use std::sync::atomic::{AtomicU16, AtomicU32};
-
-fn split_u32(dword: &mut u32) -> &mut [u16; 2] {
-    unsafe { std::mem::transmute::<&mut u32, &mut [u16; 2]>(dword) }
-}
-
-fn test_same_thread() {
-    let mut dword = AtomicU32::new(42);
-    assert_eq!(dword.load(Relaxed), 42);
-    dword.store(0xabbafafa, Relaxed);
-
-    let dword_mut = dword.get_mut();
-
-    let words_mut = split_u32(dword_mut);
-
-    let (hi_mut, lo_mut) = words_mut.split_at_mut(1);
-
-    let (hi, _) = (AtomicU16::from_mut(&mut hi_mut[0]), AtomicU16::from_mut(&mut lo_mut[0]));
-
-    unsafe {
-        // Equivalent to: hi.load(Ordering::SeqCst)
-        // We need to use intrisics to for precise error location
-        atomic_load(hi.get_mut() as *mut u16); //~ ERROR: mixed-size access on an existing atomic object
-    }
-}
-
-pub fn main() {
-    test_same_thread();
-}
diff --git a/tests/run-pass/weak_memory/extra_cpp.rs b/tests/run-pass/weak_memory/extra_cpp.rs
new file mode 100644
index 00000000000..b20ec583499
--- /dev/null
+++ b/tests/run-pass/weak_memory/extra_cpp.rs
@@ -0,0 +1,79 @@
+// compile-flags: -Zmiri-ignore-leaks
+
+// Tests operations not perfomable through C++'s atomic API
+// but doable in safe (at least sound) Rust.
+
+#![feature(atomic_from_mut)]
+
+use std::sync::atomic::Ordering::*;
+use std::sync::atomic::{AtomicU16, AtomicU32, AtomicUsize};
+use std::thread::spawn;
+
+fn static_atomic_mut(val: usize) -> &'static mut AtomicUsize {
+    let ret = Box::leak(Box::new(AtomicUsize::new(val)));
+    ret
+}
+
+fn split_u32(dword: &mut u32) -> &mut [u16; 2] {
+    unsafe { std::mem::transmute::<&mut u32, &mut [u16; 2]>(dword) }
+}
+
+fn mem_replace() {
+    let mut x = AtomicU32::new(0);
+
+    let old_x = std::mem::replace(&mut x, AtomicU32::new(42));
+
+    assert_eq!(x.load(Relaxed), 42);
+    assert_eq!(old_x.load(Relaxed), 0);
+}
+
+fn assign_to_mut() {
+    let x = static_atomic_mut(0);
+    x.store(1, Relaxed);
+
+    *x = AtomicUsize::new(2);
+
+    assert_eq!(x.load(Relaxed), 2);
+}
+
+fn get_mut_write() {
+    let x = static_atomic_mut(0);
+    x.store(1, Relaxed);
+    {
+        let x_mut = x.get_mut();
+        *x_mut = 2;
+    }
+
+    let j1 = spawn(move || x.load(Relaxed));
+
+    let r1 = j1.join().unwrap();
+    assert_eq!(r1, 2);
+}
+
+// This is technically doable in C++ with atomic_ref
+// but little literature exists atm on its involvement
+// in mixed size/atomicity accesses
+fn from_mut_split() {
+    let mut x: u32 = 0;
+
+    {
+        let x_atomic = AtomicU32::from_mut(&mut x);
+        x_atomic.store(u32::from_be(0xabbafafa), Relaxed);
+    }
+
+    let (x_hi, x_lo) = split_u32(&mut x).split_at_mut(1);
+
+    let x_hi_atomic = AtomicU16::from_mut(&mut x_hi[0]);
+    let x_lo_atomic = AtomicU16::from_mut(&mut x_lo[0]);
+
+    assert_eq!(x_hi_atomic.load(Relaxed), u16::from_be(0xabba));
+    assert_eq!(x_lo_atomic.load(Relaxed), u16::from_be(0xfafa));
+}
+
+
+pub fn main() {
+    get_mut_write();
+    from_mut_split();
+    assign_to_mut();
+    mem_replace();
+}
diff --git a/tests/run-pass/weak_memory/extra_cpp.stderr b/tests/run-pass/weak_memory/extra_cpp.stderr
new file mode 100644
index 00000000000..1d0ce4b3853
--- /dev/null
+++ b/tests/run-pass/weak_memory/extra_cpp.stderr
@@ -0,0 +1,2 @@
+warning: thread support is experimental: weak memory effects are not fully compatible with the Rust atomics memory model.
+