diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index 7110365034093..13f29724ba80e 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -3030,6 +3030,7 @@ pub fn trans_crate(sess: session::Session,
               const_values: HashMap(),
               module_data: HashMap(),
               lltypes: ty::new_ty_hash(),
+              llsizingtypes: ty::new_ty_hash(),
               names: new_namegen(sess.parse_sess.interner),
               next_addrspace: new_addrspace_gen(),
               symbol_hasher: symbol_hasher,
diff --git a/src/librustc/middle/trans/common.rs b/src/librustc/middle/trans/common.rs
index 13902be776be5..b0ec0e1b90738 100644
--- a/src/librustc/middle/trans/common.rs
+++ b/src/librustc/middle/trans/common.rs
@@ -202,6 +202,7 @@ pub struct crate_ctxt {
      const_values: HashMap<ast::node_id, ValueRef>,
      module_data: HashMap<~str, ValueRef>,
      lltypes: HashMap<ty::t, TypeRef>,
+     llsizingtypes: HashMap<ty::t, TypeRef>,
      names: namegen,
      next_addrspace: addrspace_gen,
      symbol_hasher: @hash::State,
diff --git a/src/librustc/middle/trans/machine.rs b/src/librustc/middle/trans/machine.rs
index 75e494f7bfcd9..58a53cd878a70 100644
--- a/src/librustc/middle/trans/machine.rs
+++ b/src/librustc/middle/trans/machine.rs
@@ -13,60 +13,8 @@
 
 use middle::trans::common::*;
 use middle::trans::type_of;
-use middle::ty::field;
 use middle::ty;
-
-use syntax::parse::token::special_idents;
-
-// Creates a simpler, size-equivalent type. The resulting type is guaranteed
-// to have (a) the same size as the type that was passed in; (b) to be non-
-// recursive. This is done by replacing all boxes in a type with boxed unit
-// types.
-// This should reduce all pointers to some simple pointer type, to
-// ensure that we don't recurse endlessly when computing the size of a
-// nominal type that has pointers to itself in it.
-pub fn simplify_type(tcx: ty::ctxt, typ: ty::t) -> ty::t {
-    fn nilptr(tcx: ty::ctxt) -> ty::t {
-        ty::mk_ptr(tcx, ty::mt {ty: ty::mk_nil(tcx), mutbl: ast::m_imm})
-    }
-    fn simplifier(tcx: ty::ctxt, typ: ty::t) -> ty::t {
-        match ty::get(typ).sty {
-          ty::ty_box(_) | ty::ty_opaque_box | ty::ty_uniq(_) |
-          ty::ty_evec(_, ty::vstore_uniq) | ty::ty_evec(_, ty::vstore_box) |
-          ty::ty_estr(ty::vstore_uniq) | ty::ty_estr(ty::vstore_box) |
-          ty::ty_ptr(_) | ty::ty_rptr(*) => nilptr(tcx),
-
-          ty::ty_bare_fn(*) | // FIXME(#4804) Bare fn repr
-          ty::ty_closure(*) => ty::mk_tup(tcx, ~[nilptr(tcx), nilptr(tcx)]),
-
-          ty::ty_evec(_, ty::vstore_slice(_)) |
-          ty::ty_estr(ty::vstore_slice(_)) => {
-            ty::mk_tup(tcx, ~[nilptr(tcx), ty::mk_int(tcx)])
-          }
-          // Reduce a class type to a record type in which all the fields are
-          // simplified
-          ty::ty_struct(did, ref substs) => {
-            let simpl_fields = (if ty::ty_dtor(tcx, did).is_present() {
-                // remember the drop flag
-                  ~[field {
-                    ident: special_idents::dtor,
-                    mt: ty::mt {ty: ty::mk_u8(tcx), mutbl: ast::m_mutbl}
-                   }] }
-                else { ~[] }) +
-                do ty::lookup_struct_fields(tcx, did).map |f| {
-                 let t = ty::lookup_field_type(tcx, did, f.id, substs);
-                 field {
-                    ident: f.ident,
-                    mt: ty::mt {ty: simplify_type(tcx, t), mutbl: ast::m_const
-                 }}
-            };
-            ty::mk_rec(tcx, simpl_fields)
-          }
-          _ => typ
-        }
-    }
-    ty::fold_ty(tcx, typ, |t| simplifier(tcx, t))
-}
+use util::ppaux::ty_to_str;
 
 // ______________________________________________________________________
 // compute sizeof / alignof
@@ -180,27 +128,40 @@ pub fn llalign_of(cx: @crate_ctxt, t: TypeRef) -> ValueRef {
 
 // Computes the size of the data part of an enum.
 pub fn static_size_of_enum(cx: @crate_ctxt, t: ty::t) -> uint {
-    if cx.enum_sizes.contains_key(&t) { return cx.enum_sizes.get(&t); }
+    if cx.enum_sizes.contains_key(&t) {
+        return cx.enum_sizes.get(&t);
+    }
+
+    debug!("static_size_of_enum %s", ty_to_str(cx.tcx, t));
+
     match ty::get(t).sty {
-      ty::ty_enum(tid, ref substs) => {
-        // Compute max(variant sizes).
-        let mut max_size = 0u;
-        let variants = ty::enum_variants(cx.tcx, tid);
-        for vec::each(*variants) |variant| {
-            let tup_ty = simplify_type(
-                cx.tcx,
-                ty::mk_tup(cx.tcx, /*bad*/copy variant.args));
-            // Perform any type parameter substitutions.
-            let tup_ty = ty::subst(cx.tcx, substs, tup_ty);
-            // Here we possibly do a recursive call.
-            let this_size =
-                llsize_of_real(cx, type_of::type_of(cx, tup_ty));
-            if max_size < this_size { max_size = this_size; }
+        ty::ty_enum(tid, ref substs) => {
+            // Compute max(variant sizes).
+            let mut max_size = 0;
+            let variants = ty::enum_variants(cx.tcx, tid);
+            for variants.each |variant| {
+                if variant.args.len() == 0 {
+                    loop;
+                }
+
+                let lltypes = variant.args.map(|&variant_arg| {
+                    let substituted = ty::subst(cx.tcx, substs, variant_arg);
+                    type_of::sizing_type_of(cx, substituted)
+                });
+
+                debug!("static_size_of_enum: variant %s type %s",
+                       cx.tcx.sess.str_of(variant.name),
+                       ty_str(cx.tn, T_struct(lltypes)));
+
+                let this_size = llsize_of_real(cx, T_struct(lltypes));
+                if max_size < this_size {
+                    max_size = this_size;
+                }
+            }
+            cx.enum_sizes.insert(t, max_size);
+            return max_size;
         }
-        cx.enum_sizes.insert(t, max_size);
-        return max_size;
-      }
-      _ => cx.sess.bug(~"static_size_of_enum called on non-enum")
+        _ => cx.sess.bug(~"static_size_of_enum called on non-enum")
     }
 }
 
diff --git a/src/librustc/middle/trans/type_of.rs b/src/librustc/middle/trans/type_of.rs
index 972f702c18a81..d87674f6b6e84 100644
--- a/src/librustc/middle/trans/type_of.rs
+++ b/src/librustc/middle/trans/type_of.rs
@@ -89,6 +89,95 @@ pub fn type_of_non_gc_box(cx: @crate_ctxt, t: ty::t) -> TypeRef {
     }
 }
 
+// A "sizing type" is an LLVM type, the size and alignment of which are
+// guaranteed to be equivalent to what you would get out of `type_of()`. It's
+// useful because:
+//
+// (1) It may be cheaper to compute the sizing type than the full type if all
+//     you're interested in is the size and/or alignment;
+//
+// (2) It won't make any recursive calls to determine the structure of the
+//     type behind pointers. This can help prevent infinite loops for
+//     recursive types. For example, `static_size_of_enum()` relies on this
+//     behavior.
+
+pub fn sizing_type_of(cx: @crate_ctxt, t: ty::t) -> TypeRef {
+    if cx.llsizingtypes.contains_key(&t) {
+        return cx.llsizingtypes.get(&t);
+    }
+
+    let llsizingty = match ty::get(t).sty {
+        ty::ty_nil | ty::ty_bot => T_nil(),
+        ty::ty_bool => T_bool(),
+        ty::ty_int(t) => T_int_ty(cx, t),
+        ty::ty_uint(t) => T_uint_ty(cx, t),
+        ty::ty_float(t) => T_float_ty(cx, t),
+
+        ty::ty_estr(ty::vstore_uniq) |
+        ty::ty_estr(ty::vstore_box) |
+        ty::ty_evec(_, ty::vstore_uniq) |
+        ty::ty_evec(_, ty::vstore_box) |
+        ty::ty_box(*) |
+        ty::ty_opaque_box |
+        ty::ty_uniq(*) |
+        ty::ty_ptr(*) |
+        ty::ty_rptr(*) |
+        ty::ty_type |
+        ty::ty_opaque_closure_ptr(*) => T_ptr(T_i8()),
+
+        ty::ty_estr(ty::vstore_slice(*)) |
+        ty::ty_evec(_, ty::vstore_slice(*)) => {
+            T_struct(~[T_ptr(T_i8()), T_ptr(T_i8())])
+        }
+
+        // FIXME(#4804) Bare fn repr
+        ty::ty_bare_fn(*) => T_struct(~[T_ptr(T_i8()), T_ptr(T_i8())]),
+        ty::ty_closure(*) => T_struct(~[T_ptr(T_i8()), T_ptr(T_i8())]),
+        ty::ty_trait(_, _, vstore) => T_opaque_trait(cx, vstore),
+
+        ty::ty_estr(ty::vstore_fixed(size)) => T_array(T_i8(), size),
+        ty::ty_evec(mt, ty::vstore_fixed(size)) => {
+            T_array(sizing_type_of(cx, mt.ty), size)
+        }
+
+        ty::ty_unboxed_vec(mt) => T_vec(cx, sizing_type_of(cx, mt.ty)),
+
+        ty::ty_tup(ref elems) => {
+            T_struct(elems.map(|&t| sizing_type_of(cx, t)))
+        }
+
+        ty::ty_rec(ref fields) => {
+            T_struct(fields.map(|f| sizing_type_of(cx, f.mt.ty)))
+        }
+
+        ty::ty_struct(def_id, ref substs) => {
+            let fields = ty::lookup_struct_fields(cx.tcx, def_id);
+            let lltype = T_struct(fields.map(|field| {
+                let field_type = ty::lookup_field_type(cx.tcx,
+                                                       def_id,
+                                                       field.id,
+                                                       substs);
+                sizing_type_of(cx, field_type)
+            }));
+            if ty::ty_dtor(cx.tcx, def_id).is_present() {
+                T_struct(~[lltype, T_i8()])
+            } else {
+                lltype
+            }
+        }
+
+        ty::ty_enum(def_id, _) => T_struct(enum_body_types(cx, def_id, t)),
+
+        ty::ty_self | ty::ty_infer(*) | ty::ty_param(*) | ty::ty_err(*) => {
+            cx.tcx.sess.bug(~"fictitious type in sizing_type_of()")
+        }
+    };
+
+    cx.llsizingtypes.insert(t, llsizingty);
+    llsizingty
+}
+
+// NB: If you update this, be sure to update `sizing_type_of()` as well.
 pub fn type_of(cx: @crate_ctxt, t: ty::t) -> TypeRef {
     debug!("type_of %?: %?", t, ty::get(t));
 
@@ -236,23 +325,23 @@ pub fn type_of(cx: @crate_ctxt, t: ty::t) -> TypeRef {
     return llty;
 }
 
-pub fn fill_type_of_enum(cx: @crate_ctxt, did: ast::def_id, t: ty::t,
-                         llty: TypeRef) {
+pub fn enum_body_types(cx: @crate_ctxt, did: ast::def_id, t: ty::t)
+                    -> ~[TypeRef] {
+    let univar = ty::enum_is_univariant(cx.tcx, did);
+    let size = machine::static_size_of_enum(cx, t);
+    if !univar {
+        ~[T_enum_discrim(cx), T_array(T_i8(), size)]
+    } else {
+        ~[T_array(T_i8(), size)]
+    }
+}
 
+pub fn fill_type_of_enum(cx: @crate_ctxt,
+                         did: ast::def_id,
+                         t: ty::t,
+                         llty: TypeRef) {
     debug!("type_of_enum %?: %?", t, ty::get(t));
-
-    let lltys = {
-        let univar = ty::enum_is_univariant(cx.tcx, did);
-        let size = machine::static_size_of_enum(cx, t);
-        if !univar {
-            ~[T_enum_discrim(cx), T_array(T_i8(), size)]
-        }
-        else {
-            ~[T_array(T_i8(), size)]
-        }
-    };
-
-    common::set_struct_body(llty, lltys);
+    common::set_struct_body(llty, enum_body_types(cx, did, t));
 }
 
 // Want refinements! (Or case classes, I guess