rustc: fix const enums to be packed, r=burningtree.

Author: graydon

src/librustc/middle/trans/common.rs

@@ -1209,6 +1209,14 @@ fn C_struct(elts: &[ValueRef]) -> ValueRef {
     }
 }
 
+fn C_packed_struct(elts: &[ValueRef]) -> ValueRef {
+    unsafe {
+        do vec::as_imm_buf(elts) |ptr, len| {
+            llvm::LLVMConstStruct(ptr, len as c_uint, True)
+        }
+    }
+}
+
 fn C_named_struct(T: TypeRef, elts: &[ValueRef]) -> ValueRef {
     unsafe {
         do vec::as_imm_buf(elts) |ptr, len| {

src/librustc/middle/trans/consts.rs

@@ -455,15 +455,14 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
                 let discrim = base::get_discrim_val(cx, e.span, tid, vid);
                 let c_args = C_struct(args.map(|a| const_expr(cx, *a)));
 
-                let fields = if !degen {
-                    ~[discrim, c_args]
+                // FIXME (#1645): enum body alignment is generaly wrong.
+                if !degen {
+                    C_packed_struct(~[discrim, c_args])
                 } else if size == 0 {
-                    ~[discrim]
+                    C_struct(~[discrim])
                 } else {
-                    ~[c_args]
-                };
-
-                C_struct(fields)
+                    C_struct(~[c_args])
+                }
             }
                 _ => cx.sess.span_bug(e.span, ~"expected a struct def")
             }