don't panic on pointer to value comparison in primvals

src/primval.rs

@@ -289,7 +289,7 @@ pub fn binary_op<'tcx>(
         }
 
         (None, None) => {}
-        _ => unimplemented!(),
+        _ => return Err(EvalError::ReadPointerAsBytes),
     }
 
     let (l, r) = (left.bits, right.bits);

tests/compile-fail/tag-align-dyn-u64.rs

@@ -0,0 +1,37 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(dead_code)]
+
+use std::mem;
+
+enum Tag<A> {
+    Tag2(A)
+}
+
+struct Rec {
+    c8: u8,
+    t: Tag<u64>
+}
+
+fn mk_rec() -> Rec {
+    return Rec { c8:0, t:Tag::Tag2(0) };
+}
+
+fn is_u64_aligned(u: &Tag<u64>) -> bool {
+    let p: usize = unsafe { mem::transmute(u) };
+    let u64_align = std::mem::align_of::<u64>();
+    return (p & (u64_align - 1)) == 0; //~ ERROR a raw memory access tried to access part of a pointer value as raw bytes
+}
+
+pub fn main() {
+    let x = mk_rec();
+    assert!(is_u64_aligned(&x.t));
+}