Add a regression test for copy propagation miscompilation

src/test/ui/mir/issue-76740-copy-propagation.rs

@@ -0,0 +1,30 @@
+// Regression test for issue #76740.
+// run-fail FIXME: change to run-pass once #76899 lands
+// compile-flags: -Zmir-opt-level=3
+
+#[derive(Copy, Clone)]
+pub struct V([usize; 4]);
+
+impl V {
+    fn new() -> Self {
+        V([0; 4])
+    }
+
+    #[inline(never)]
+    fn check(mut self) {
+        assert_eq!(self.0[0], 0);
+        self.0[0] = 1;
+    }
+}
+
+fn main() {
+    let v = V::new();
+    let mut i = 0;
+    while i != 10 {
+        // Copy propagation incorrectly assumed that Operand::Move does not
+        // mutate the local, and used the same v for each V::check call,
+        // rather than a copy.
+        v.check();
+        i += 1;
+    }
+}