Fix dest prop miscompilation around references

Author: jonas-schievink

compiler/rustc_mir/src/transform/dest_prop.rs

@@ -905,7 +905,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindAssignments<'a, 'tcx> {
             // FIXME: This can be smarter and take `StorageDead` into account (which
             // invalidates borrows).
             if self.ever_borrowed_locals.contains(dest.local)
-                && self.ever_borrowed_locals.contains(src.local)
+                || self.ever_borrowed_locals.contains(src.local)
             {
                 return;
             }

src/test/ui/issues/issue-77002.rs

@@ -0,0 +1,16 @@
+// compile-flags: -Zmir-opt-level=2 -Copt-level=0
+// run-pass
+
+type M = [i64; 2];
+
+fn f(a: &M) -> M {
+    let mut b: M = M::default();
+    b[0] = a[0] * a[0];
+    b
+}
+
+fn main() {
+    let mut a: M = [1, 1];
+    a = f(&a);
+    assert_eq!(a[0], 1);
+}