Auto merge of rust-lang#3010 - RalfJung:assign_overlapping, r=RalfJung

add test checking that overlapping assignments work

Author: bors

src/tools/miri/tests/pass/ptr_raw.rs

@@ -20,6 +20,15 @@ fn basic_raw() {
     assert_eq!(*x, 23);
 }
 
+fn assign_overlapping() {
+    // Test an assignment where LHS and RHS alias.
+    // In Mir, that's UB (see `fail/overlapping_assignment.rs`), but in surface Rust this is allowed.
+    let mut mem = [0u32; 4];
+    let ptr = &mut mem as *mut [u32; 4];
+    unsafe { *ptr = *ptr };
+}
+
 fn main() {
     basic_raw();
+    assign_overlapping();
 }