diff --git a/src/librustc_trans/trans/base.rs b/src/librustc_trans/trans/base.rs
index 88ce36a710a0c..ea98d6bb74e95 100644
--- a/src/librustc_trans/trans/base.rs
+++ b/src/librustc_trans/trans/base.rs
@@ -1054,6 +1054,11 @@ pub fn load_ty<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
         C_undef(type_of::type_of(cx.ccx(), t))
     } else if ty::type_is_bool(t) {
         Trunc(cx, LoadRangeAssert(cx, ptr, 0, 2, llvm::False), Type::i1(cx.ccx()))
+    } else if type_is_immediate(cx.ccx(), t) && type_of::type_of(cx.ccx(), t).is_aggregate() {
+        // We want to pass small aggregates as immediate values, but using an aggregate LLVM type
+        // for this leads to bad optimizations, so its arg type is an appropriately sized integer
+        // and we have to convert it
+        Load(cx, BitCast(cx, ptr, type_of::arg_type_of(cx.ccx(), t).ptr_to()))
     } else if ty::type_is_char(t) {
         // a char is a Unicode codepoint, and so takes values from 0
         // to 0x10FFFF inclusive only.
@@ -1065,9 +1070,14 @@ pub fn load_ty<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
 
 /// Helper for storing values in memory. Does the necessary conversion if the in-memory type
 /// differs from the type used for SSA values.
-pub fn store_ty(cx: Block, v: ValueRef, dst: ValueRef, t: Ty) {
+pub fn store_ty<'blk, 'tcx>(cx: Block<'blk, 'tcx>, v: ValueRef, dst: ValueRef, t: Ty<'tcx>) {
     if ty::type_is_bool(t) {
         Store(cx, ZExt(cx, v, Type::i8(cx.ccx())), dst);
+    } else if type_is_immediate(cx.ccx(), t) && type_of::type_of(cx.ccx(), t).is_aggregate() {
+        // We want to pass small aggregates as immediate values, but using an aggregate LLVM type
+        // for this leads to bad optimizations, so its arg type is an appropriately sized integer
+        // and we have to convert it
+        Store(cx, v, BitCast(cx, dst, type_of::arg_type_of(cx.ccx(), t).ptr_to()));
     } else {
         Store(cx, v, dst);
     };
diff --git a/src/librustc_trans/trans/common.rs b/src/librustc_trans/trans/common.rs
index 3afd33d324dd1..f59e70d099a63 100644
--- a/src/librustc_trans/trans/common.rs
+++ b/src/librustc_trans/trans/common.rs
@@ -222,10 +222,7 @@ fn type_is_newtype_immediate<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     match ty.sty {
         ty::ty_struct(def_id, substs) => {
             let fields = ty::struct_fields(ccx.tcx(), def_id, substs);
-            fields.len() == 1 &&
-                fields[0].name ==
-                    token::special_idents::unnamed_field.name &&
-                type_is_immediate(ccx, fields[0].mt.ty)
+            fields.len() == 1 && type_is_immediate(ccx, fields[0].mt.ty)
         }
         _ => false
     }
@@ -247,7 +244,7 @@ pub fn type_is_immediate<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, ty: Ty<'tcx>) -
         return false;
     }
     match ty.sty {
-        ty::ty_struct(..) | ty::ty_enum(..) | ty::ty_tup(..) |
+        ty::ty_struct(..) | ty::ty_enum(..) | ty::ty_tup(..) | ty::ty_vec(_, Some(_)) |
         ty::ty_unboxed_closure(..) => {
             let llty = sizing_type_of(ccx, ty);
             llsize_of_alloc(ccx, llty) <= llsize_of_alloc(ccx, ccx.int_type())
diff --git a/src/librustc_trans/trans/foreign.rs b/src/librustc_trans/trans/foreign.rs
index 3dfb36c854b72..fb61bab6ade2c 100644
--- a/src/librustc_trans/trans/foreign.rs
+++ b/src/librustc_trans/trans/foreign.rs
@@ -736,6 +736,13 @@ pub fn trans_rust_fn_with_foreign_abi<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                 if ty::type_is_bool(rust_ty) {
                     let tmp = builder.load_range_assert(llforeign_arg, 0, 2, llvm::False);
                     builder.trunc(tmp, Type::i1(ccx))
+                } else if type_of::type_of(ccx, rust_ty).is_aggregate() {
+                    // We want to pass small aggregates as immediate values, but using an aggregate
+                    // LLVM type for this leads to bad optimizations, so its arg type is an
+                    // appropriately sized integer and we have to convert it
+                    let tmp = builder.bitcast(llforeign_arg,
+                                              type_of::arg_type_of(ccx, rust_ty).ptr_to());
+                    builder.load(tmp)
                 } else {
                     builder.load(llforeign_arg)
                 }
@@ -834,10 +841,10 @@ fn foreign_signature<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                fn_sig: &ty::FnSig<'tcx>,
                                arg_tys: &[Ty<'tcx>])
                                -> LlvmSignature {
-    let llarg_tys = arg_tys.iter().map(|&arg| arg_type_of(ccx, arg)).collect();
+    let llarg_tys = arg_tys.iter().map(|&arg| foreign_arg_type_of(ccx, arg)).collect();
     let (llret_ty, ret_def) = match fn_sig.output {
         ty::FnConverging(ret_ty) =>
-            (type_of::arg_type_of(ccx, ret_ty), !return_type_is_void(ccx, ret_ty)),
+            (type_of::foreign_arg_type_of(ccx, ret_ty), !return_type_is_void(ccx, ret_ty)),
         ty::FnDiverging =>
             (Type::nil(ccx), false)
     };
diff --git a/src/librustc_trans/trans/glue.rs b/src/librustc_trans/trans/glue.rs
index 2219cd59263cc..a79bb6ca16470 100644
--- a/src/librustc_trans/trans/glue.rs
+++ b/src/librustc_trans/trans/glue.rs
@@ -138,7 +138,7 @@ pub fn drop_ty_immediate<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                      -> Block<'blk, 'tcx> {
     let _icx = push_ctxt("drop_ty_immediate");
     let vp = alloca(bcx, type_of(bcx.ccx(), t), "");
-    Store(bcx, v, vp);
+    store_ty(bcx, v, vp, t);
     drop_ty(bcx, vp, t, source_location)
 }
 
diff --git a/src/librustc_trans/trans/intrinsic.rs b/src/librustc_trans/trans/intrinsic.rs
index b22c7f763f035..91c7409182df6 100644
--- a/src/librustc_trans/trans/intrinsic.rs
+++ b/src/librustc_trans/trans/intrinsic.rs
@@ -357,11 +357,11 @@ pub fn trans_intrinsic_call<'a, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
                 &ccx.link_meta().crate_hash);
             // NB: This needs to be kept in lockstep with the TypeId struct in
             //     the intrinsic module
-            C_named_struct(llret_ty, &[C_u64(ccx, hash)])
+            C_u64(ccx, hash)
         }
         (_, "init") => {
             let tp_ty = *substs.types.get(FnSpace, 0);
-            let lltp_ty = type_of::type_of(ccx, tp_ty);
+            let lltp_ty = type_of::arg_type_of(ccx, tp_ty);
             if return_type_is_void(ccx, tp_ty) {
                 C_nil(ccx)
             } else {
@@ -686,6 +686,11 @@ fn with_overflow_intrinsic<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, name: &'static st
     let ret = C_undef(type_of::type_of(bcx.ccx(), t));
     let ret = InsertValue(bcx, ret, result, 0);
     let ret = InsertValue(bcx, ret, overflow, 1);
-
-    ret
+    if type_is_immediate(bcx.ccx(), t) {
+        let tmp = alloc_ty(bcx, t, "tmp");
+        Store(bcx, ret, tmp);
+        load_ty(bcx, tmp, t)
+    } else {
+        ret
+    }
 }
diff --git a/src/librustc_trans/trans/type_.rs b/src/librustc_trans/trans/type_.rs
index 71a7789eb3932..9cae142c03ac1 100644
--- a/src/librustc_trans/trans/type_.rs
+++ b/src/librustc_trans/trans/type_.rs
@@ -82,6 +82,11 @@ impl Type {
         ty!(llvm::LLVMInt64TypeInContext(ccx.llcx()))
     }
 
+    // Creates an integer type with the given number of bits, e.g. i24
+    pub fn ix(ccx: &CrateContext, num_bits: u64) -> Type {
+        ty!(llvm::LLVMIntTypeInContext(ccx.llcx(), num_bits as c_uint))
+    }
+
     pub fn f32(ccx: &CrateContext) -> Type {
         ty!(llvm::LLVMFloatTypeInContext(ccx.llcx()))
     }
@@ -260,6 +265,13 @@ impl Type {
         ty!(llvm::LLVMPointerType(self.to_ref(), 0))
     }
 
+    pub fn is_aggregate(&self) -> bool {
+        match self.kind() {
+            TypeKind::Struct | TypeKind::Array => true,
+            _ =>  false
+        }
+    }
+
     pub fn is_packed(&self) -> bool {
         unsafe {
             llvm::LLVMIsPackedStruct(self.to_ref()) == True
diff --git a/src/librustc_trans/trans/type_of.rs b/src/librustc_trans/trans/type_of.rs
index 9933079742229..76e0e0d054557 100644
--- a/src/librustc_trans/trans/type_of.rs
+++ b/src/librustc_trans/trans/type_of.rs
@@ -243,9 +243,24 @@ pub fn sizing_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Typ
     llsizingty
 }
 
+pub fn foreign_arg_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Type {
+    if ty::type_is_bool(t) {
+        Type::i1(cx)
+    } else {
+        type_of(cx, t)
+    }
+}
+
 pub fn arg_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Type {
     if ty::type_is_bool(t) {
         Type::i1(cx)
+    } else if type_is_immediate(cx, t) && type_of(cx, t).is_aggregate() {
+        // We want to pass small aggregates as immediate values, but using an aggregate LLVM type
+        // for this leads to bad optimizations, so its arg type is an appropriately sized integer
+        match machine::llsize_of_alloc(cx, sizing_type_of(cx, t)) {
+            0 => type_of(cx, t),
+            n => Type::ix(cx, n * 8),
+        }
     } else {
         type_of(cx, t)
     }