Ignore unsized types when trying to determine the size of a type

compiler/rustc_lint/src/reference_casting.rs

@@ -194,6 +194,12 @@ fn is_cast_to_bigger_memory_layout<'tcx>(
         return None;
     };
 
+    // if the type is not Sized we cannot know by definition it's size
+    // so we bail out
+    if !inner_start_ty.is_sized(cx.tcx, cx.param_env) {
+        return None;
+    }
+
     // try to find the underlying allocation
     let e_alloc = cx.expr_or_init(e);
     let e_alloc =

tests/ui/lint/reference_casting.rs

@@ -239,6 +239,11 @@ unsafe fn bigger_layout() {
         //~^ ERROR casting references to a bigger memory layout
     }
 
+    {
+        let x: Box<dyn Send> = Box::new(0i32);
+        let _z = unsafe { &*(&*x as *const dyn Send as *const i32) };
+    }
+
     unsafe fn from_ref(this: &i32) -> &i64 {
         &*(this as *const i32 as *const i64)
     }