Fix passing self by value for types passed by value

For types that are passed by value, we can't just cast the value to a
pointer, but have to use an alloca and copy the value there. This
handling is already present for all other arguments, but was missing
for "self".

Fixes rust-lang#6682, rust-lang#4850 and rust-lang#4878

src/librustc/middle/trans/base.rs

@@ -1730,8 +1730,15 @@ pub fn copy_args_to_allocas(fcx: fn_ctxt,
         // We really should do this regardless of whether self is owned, but
         // it doesn't work right with default method impls yet. (FIXME: #2794)
         if slf.is_owned {
-            let self_val = PointerCast(bcx, slf.v,
-                                       T_ptr(type_of(bcx.ccx(), slf.t)));
+            let self_val = if datum::appropriate_mode(slf.t).is_by_value() {
+                let tmp = BitCast(bcx, slf.v, type_of(bcx.ccx(), slf.t));
+                let alloc = alloc_ty(bcx, slf.t);
+                Store(bcx, tmp, alloc);
+                alloc
+            } else {
+                PointerCast(bcx, slf.v, T_ptr(type_of(bcx.ccx(), slf.t)))
+            };
+
             fcx.llself = Some(ValSelfData {v: self_val, ..slf});
             add_clean(bcx, self_val, slf.t);
         }