diff --git a/src/librustc/middle/trans/adt.rs b/src/librustc/middle/trans/adt.rs
index 33ad05977edb..f7fb6646938f 100644
--- a/src/librustc/middle/trans/adt.rs
+++ b/src/librustc/middle/trans/adt.rs
@@ -641,7 +641,7 @@ pub fn trans_start_init(bcx: &Block, r: &Repr, val: ValueRef, discr: Disr) {
         }
         Univariant(ref st, true) => {
             assert_eq!(discr, 0);
-            Store(bcx, C_bool(bcx.ccx(), true),
+            Store(bcx, C_u8(bcx.ccx(), 1),
                   GEPi(bcx, val, [0, st.fields.len() - 1]))
         }
         Univariant(..) => {
diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index b2558cdd364c..3eaa17a05712 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -959,10 +959,42 @@ pub fn need_invoke(bcx: &Block) -> bool {
 
 pub fn load_if_immediate(cx: &Block, v: ValueRef, t: ty::t) -> ValueRef {
     let _icx = push_ctxt("load_if_immediate");
-    if type_is_immediate(cx.ccx(), t) { return Load(cx, v); }
+    if type_is_immediate(cx.ccx(), t) { return load_ty(cx, v, t); }
     return v;
 }
 
+pub fn load_ty(cx: &Block, ptr: ValueRef, t: ty::t) -> ValueRef {
+    /*!
+     * Helper for loading values from memory. Does the necessary conversion if
+     * the in-memory type differs from the type used for SSA values. Also
+     * handles various special cases where the type gives us better information
+     * about what we are loading.
+     */
+    if type_is_zero_size(cx.ccx(), t) {
+        C_undef(type_of::type_of(cx.ccx(), t))
+    } else if ty::type_is_bool(t) {
+        Trunc(cx, LoadRangeAssert(cx, ptr, 0, 2, lib::llvm::False), Type::i1(cx.ccx()))
+    } else if ty::type_is_char(t) {
+        // a char is a unicode codepoint, and so takes values from 0
+        // to 0x10FFFF inclusive only.
+        LoadRangeAssert(cx, ptr, 0, 0x10FFFF + 1, lib::llvm::False)
+    } else {
+        Load(cx, ptr)
+    }
+}
+
+pub fn store_ty(cx: &Block, v: ValueRef, dst: ValueRef, t: ty::t) {
+    /*!
+     * Helper for storing values in memory. Does the necessary conversion if
+     * the in-memory type differs from the type used for SSA values.
+     */
+    if ty::type_is_bool(t) {
+        Store(cx, ZExt(cx, v, Type::i8(cx.ccx())), dst);
+    } else {
+        Store(cx, v, dst);
+    };
+}
+
 pub fn ignore_lhs(_bcx: &Block, local: &ast::Local) -> bool {
     match local.pat.node {
         ast::PatWild => true, _ => false
@@ -1285,9 +1317,14 @@ fn copy_args_to_allocas<'a>(fcx: &FunctionContext<'a>,
 // Ties up the llstaticallocas -> llloadenv -> lltop edges,
 // and builds the return block.
 pub fn finish_fn<'a>(fcx: &'a FunctionContext<'a>,
-                     last_bcx: &'a Block<'a>) {
+                     last_bcx: &'a Block<'a>,
+                     retty: ty::t) {
     let _icx = push_ctxt("finish_fn");
 
+    // This shouldn't need to recompute the return type,
+    // as new_fn_ctxt did it already.
+    let substd_retty = retty.substp(fcx.ccx.tcx(), fcx.param_substs);
+
     let ret_cx = match fcx.llreturn.get() {
         Some(llreturn) => {
             if !last_bcx.terminated.get() {
@@ -1297,13 +1334,13 @@ pub fn finish_fn<'a>(fcx: &'a FunctionContext<'a>,
         }
         None => last_bcx
     };
-    build_return_block(fcx, ret_cx);
+    build_return_block(fcx, ret_cx, substd_retty);
     debuginfo::clear_source_location(fcx);
     fcx.cleanup();
 }
 
 // Builds the return block for a function.
-pub fn build_return_block(fcx: &FunctionContext, ret_cx: &Block) {
+pub fn build_return_block(fcx: &FunctionContext, ret_cx: &Block, retty: ty::t) {
     // Return the value if this function immediate; otherwise, return void.
     if fcx.llretptr.get().is_none() || fcx.caller_expects_out_pointer {
         return RetVoid(ret_cx);
@@ -1321,13 +1358,16 @@ pub fn build_return_block(fcx: &FunctionContext, ret_cx: &Block) {
                 retptr.erase_from_parent();
             }
 
-            retval
+            if ty::type_is_bool(retty) {
+                Trunc(ret_cx, retval, Type::i1(fcx.ccx))
+            } else {
+                retval
+            }
         }
         // Otherwise, load the return value from the ret slot
-        None => Load(ret_cx, fcx.llretptr.get().unwrap())
+        None => load_ty(ret_cx, fcx.llretptr.get().unwrap(), retty)
     };
 
-
     Ret(ret_cx, retval);
 }
 
@@ -1429,7 +1469,7 @@ pub fn trans_closure(ccx: &CrateContext,
     }
 
     // Insert the mandatory first few basic blocks before lltop.
-    finish_fn(&fcx, bcx);
+    finish_fn(&fcx, bcx, output_type);
 }
 
 // trans_fn: creates an LLVM function corresponding to a source language
@@ -1521,7 +1561,7 @@ fn trans_enum_variant_or_tuple_like_struct(ccx: &CrateContext,
         }
     }
 
-    finish_fn(&fcx, bcx);
+    finish_fn(&fcx, bcx, result_ty);
 }
 
 fn trans_enum_def(ccx: &CrateContext, enum_definition: &ast::EnumDef,
diff --git a/src/librustc/middle/trans/cabi_arm.rs b/src/librustc/middle/trans/cabi_arm.rs
index 01bef64ebba6..c44a4e02ad46 100644
--- a/src/librustc/middle/trans/cabi_arm.rs
+++ b/src/librustc/middle/trans/cabi_arm.rs
@@ -85,7 +85,7 @@ fn ty_size(ty: Type) -> uint {
 
 fn classify_ret_ty(ccx: &CrateContext, ty: Type) -> ArgType {
     if is_reg_ty(ty) {
-        let attr = if ty == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+        let attr = if ty == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
         return ArgType::direct(ty, None, None, attr);
     }
     let size = ty_size(ty);
@@ -104,7 +104,7 @@ fn classify_ret_ty(ccx: &CrateContext, ty: Type) -> ArgType {
 
 fn classify_arg_ty(ccx: &CrateContext, ty: Type) -> ArgType {
     if is_reg_ty(ty) {
-        let attr = if ty == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+        let attr = if ty == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
         return ArgType::direct(ty, None, None, attr);
     }
     let align = ty_align(ty);
diff --git a/src/librustc/middle/trans/cabi_mips.rs b/src/librustc/middle/trans/cabi_mips.rs
index 60db609e59ed..9e5b38d2f7dd 100644
--- a/src/librustc/middle/trans/cabi_mips.rs
+++ b/src/librustc/middle/trans/cabi_mips.rs
@@ -85,7 +85,7 @@ fn ty_size(ty: Type) -> uint {
 
 fn classify_ret_ty(ccx: &CrateContext, ty: Type) -> ArgType {
     if is_reg_ty(ty) {
-        let attr = if ty == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+        let attr = if ty == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
         ArgType::direct(ty, None, None, attr)
     } else {
         ArgType::indirect(ty, Some(StructRetAttribute))
@@ -102,7 +102,7 @@ fn classify_arg_ty(ccx: &CrateContext, ty: Type, offset: &mut uint) -> ArgType {
     *offset += align_up_to(size, align * 8) / 8;
 
     if is_reg_ty(ty) {
-        let attr = if ty == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+        let attr = if ty == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
         ArgType::direct(ty, None, None, attr)
     } else {
         ArgType::direct(
diff --git a/src/librustc/middle/trans/cabi_x86.rs b/src/librustc/middle/trans/cabi_x86.rs
index 5fffdf08646b..0d88c611cbae 100644
--- a/src/librustc/middle/trans/cabi_x86.rs
+++ b/src/librustc/middle/trans/cabi_x86.rs
@@ -59,7 +59,7 @@ pub fn compute_abi_info(ccx: &CrateContext,
             }
         }
     } else {
-        let attr = if rty == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+        let attr = if rty == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
         ret_ty = ArgType::direct(rty, None, None, attr);
     }
 
@@ -74,7 +74,7 @@ pub fn compute_abi_info(ccx: &CrateContext,
                 }
             }
             _ => {
-                let attr = if t == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+                let attr = if t == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
                 ArgType::direct(t, None, None, attr)
             }
         };
diff --git a/src/librustc/middle/trans/cabi_x86_64.rs b/src/librustc/middle/trans/cabi_x86_64.rs
index b2cd9d256dd4..5b8ddfe1be7b 100644
--- a/src/librustc/middle/trans/cabi_x86_64.rs
+++ b/src/librustc/middle/trans/cabi_x86_64.rs
@@ -350,7 +350,7 @@ pub fn compute_abi_info(ccx: &CrateContext,
                                 None)
             }
         } else {
-            let attr = if ty == Type::bool(ccx) { Some(ZExtAttribute) } else { None };
+            let attr = if ty == Type::i1(ccx) { Some(ZExtAttribute) } else { None };
             ArgType::direct(ty, None, None, attr)
         }
     }
diff --git a/src/librustc/middle/trans/callee.rs b/src/librustc/middle/trans/callee.rs
index dc9828606cc3..37b9da738e15 100644
--- a/src/librustc/middle/trans/callee.rs
+++ b/src/librustc/middle/trans/callee.rs
@@ -346,7 +346,7 @@ pub fn trans_unboxing_shim(bcx: &Block,
                            }).bcx;
 
     bcx = fcx.pop_and_trans_custom_cleanup_scope(bcx, arg_scope);
-    finish_fn(&fcx, bcx);
+    finish_fn(&fcx, bcx, return_type);
 
     llfn
 }
@@ -758,7 +758,7 @@ pub fn trans_call_inner<'a>(
                 if !type_of::return_uses_outptr(bcx.ccx(), ret_ty) &&
                     !type_is_zero_size(bcx.ccx(), ret_ty)
                 {
-                    Store(bcx, llret, llretslot);
+                    store_ty(bcx, llret, llretslot, ret_ty)
                 }
             }
             None => {}
diff --git a/src/librustc/middle/trans/datum.rs b/src/librustc/middle/trans/datum.rs
index 440aa36b28cb..b93469ad2fba 100644
--- a/src/librustc/middle/trans/datum.rs
+++ b/src/librustc/middle/trans/datum.rs
@@ -13,10 +13,8 @@
  * Datums are and how they are intended to be used.
  */
 
-use lib;
 use lib::llvm::ValueRef;
 use middle::trans::base::*;
-use middle::trans::build::*;
 use middle::trans::common::*;
 use middle::trans::cleanup;
 use middle::trans::cleanup::CleanupMethods;
@@ -344,7 +342,7 @@ impl Datum<Rvalue> {
                 match self.kind.mode {
                     ByValue => DatumBlock::new(bcx, self),
                     ByRef => {
-                        let llval = load(bcx, self.val, self.ty);
+                        let llval = load_ty(bcx, self.val, self.ty);
                         DatumBlock::new(bcx, Datum::new(llval, self.ty, Rvalue::new(ByValue)))
                     }
                 }
@@ -471,7 +469,7 @@ impl Datum<Expr> {
                         DatumBlock::new(bcx, scratch)
                     }
                     ByValue => {
-                        let v = load(bcx, l.val, l.ty);
+                        let v = load_ty(bcx, l.val, l.ty);
                         bcx = l.kind.post_store(bcx, l.val, l.ty);
                         DatumBlock::new(bcx, Datum::new(v, l.ty, Rvalue::new(ByValue)))
                     }
@@ -516,24 +514,6 @@ impl Datum<Lvalue> {
     }
 }
 
-fn load<'a>(bcx: &'a Block<'a>, llptr: ValueRef, ty: ty::t) -> ValueRef {
-    /*!
-     * Private helper for loading from a by-ref datum. Handles various
-     * special cases where the type gives us better information about
-     * what we are loading.
-     */
-
-    if type_is_zero_size(bcx.ccx(), ty) {
-        C_undef(type_of::type_of(bcx.ccx(), ty))
-    } else if ty::type_is_char(ty) {
-        // a char is a unicode codepoint, and so takes values from 0
-        // to 0x10FFFF inclusive only.
-        LoadRangeAssert(bcx, llptr, 0, 0x10FFFF + 1, lib::llvm::False)
-    } else {
-        Load(bcx, llptr)
-    }
-}
-
 /**
  * Generic methods applicable to any sort of datum.
  */
@@ -591,7 +571,7 @@ impl<K:KindOps> Datum<K> {
         if self.kind.is_by_ref() {
             memcpy_ty(bcx, dst, self.val, self.ty);
         } else {
-            Store(bcx, self.val, dst);
+            store_ty(bcx, self.val, dst, self.ty);
         }
 
         return bcx;
@@ -642,7 +622,7 @@ impl<K:KindOps> Datum<K> {
         assert!(!ty::type_needs_drop(bcx.tcx(), self.ty));
         assert!(self.appropriate_rvalue_mode(bcx.ccx()) == ByValue);
         if self.kind.is_by_ref() {
-            load(bcx, self.val, self.ty)
+            load_ty(bcx, self.val, self.ty)
         } else {
             self.val
         }
diff --git a/src/librustc/middle/trans/expr.rs b/src/librustc/middle/trans/expr.rs
index aad82f370289..ac33f9bd1a87 100644
--- a/src/librustc/middle/trans/expr.rs
+++ b/src/librustc/middle/trans/expr.rs
@@ -1374,7 +1374,7 @@ fn trans_lazy_binop<'a>(
     }
 
     Br(past_rhs, join.llbb);
-    let phi = Phi(join, Type::bool(bcx.ccx()), [lhs, rhs],
+    let phi = Phi(join, Type::i1(bcx.ccx()), [lhs, rhs],
                   [past_lhs.llbb, past_rhs.llbb]);
 
     return immediate_rvalue_bcx(join, phi, binop_ty).to_expr_datumblock();
@@ -1591,8 +1591,8 @@ fn trans_imm_cast<'a>(bcx: &'a Block<'a>,
     let k_in = cast_type_kind(t_in);
     let k_out = cast_type_kind(t_out);
     let s_in = k_in == cast_integral && ty::type_is_signed(t_in);
-    let ll_t_in = type_of::type_of(ccx, t_in);
-    let ll_t_out = type_of::type_of(ccx, t_out);
+    let ll_t_in = type_of::arg_type_of(ccx, t_in);
+    let ll_t_out = type_of::arg_type_of(ccx, t_out);
 
     // Convert the value to be cast into a ValueRef, either by-ref or
     // by-value as appropriate given its type:
@@ -1683,7 +1683,7 @@ fn trans_assign_op<'a>(
     let dst_datum = unpack_datum!(bcx, trans_to_lvalue(bcx, dst, "assign_op"));
     assert!(!ty::type_needs_drop(bcx.tcx(), dst_datum.ty));
     let dst_ty = dst_datum.ty;
-    let dst = Load(bcx, dst_datum.val);
+    let dst = load_ty(bcx, dst_datum.val, dst_datum.ty);
 
     // Evaluate RHS
     let rhs_datum = unpack_datum!(bcx, trans(bcx, &*src));
diff --git a/src/librustc/middle/trans/foreign.rs b/src/librustc/middle/trans/foreign.rs
index 6d719873c768..4e009622b0eb 100644
--- a/src/librustc/middle/trans/foreign.rs
+++ b/src/librustc/middle/trans/foreign.rs
@@ -325,7 +325,7 @@ pub fn trans_native_call<'a>(
                 base::alloca(bcx,
                              type_of::type_of(ccx, *passed_arg_tys.get(i)),
                              "__arg");
-            Store(bcx, llarg_rust, scratch);
+            base::store_ty(bcx, llarg_rust, scratch, *passed_arg_tys.get(i));
             llarg_rust = scratch;
         }
 
@@ -346,7 +346,12 @@ pub fn trans_native_call<'a>(
         let llarg_foreign = if foreign_indirect {
             llarg_rust
         } else {
-            Load(bcx, llarg_rust)
+            if ty::type_is_bool(*passed_arg_tys.get(i)) {
+                let val = LoadRangeAssert(bcx, llarg_rust, 0, 2, lib::llvm::False);
+                Trunc(bcx, val, Type::i1(bcx.ccx()))
+            } else {
+                Load(bcx, llarg_rust)
+            }
         };
 
         debug!("argument {}, llarg_foreign={}",
@@ -431,7 +436,7 @@ pub fn trans_native_call<'a>(
         debug!("llforeign_ret_ty={}", ccx.tn.type_to_str(llforeign_ret_ty));
 
         if llrust_ret_ty == llforeign_ret_ty {
-            Store(bcx, llforeign_retval, llretptr);
+            base::store_ty(bcx, llforeign_retval, llretptr, fn_sig.output)
         } else {
             // The actual return type is a struct, but the ABI
             // adaptation code has cast it into some scalar type.  The
@@ -715,9 +720,15 @@ pub fn trans_rust_fn_with_foreign_abi(ccx: &CrateContext,
             // pointer).  It makes adapting types easier, since we can
             // always just bitcast pointers.
             if !foreign_indirect {
-                let lltemp = builder.alloca(val_ty(llforeign_arg), "");
-                builder.store(llforeign_arg, lltemp);
-                llforeign_arg = lltemp;
+                llforeign_arg = if ty::type_is_bool(rust_ty) {
+                    let lltemp = builder.alloca(Type::bool(ccx), "");
+                    builder.store(builder.zext(llforeign_arg, Type::bool(ccx)), lltemp);
+                    lltemp
+                } else {
+                    let lltemp = builder.alloca(val_ty(llforeign_arg), "");
+                    builder.store(llforeign_arg, lltemp);
+                    lltemp
+                }
             }
 
             // If the types in the ABI and the Rust types don't match,
@@ -731,7 +742,12 @@ pub fn trans_rust_fn_with_foreign_abi(ccx: &CrateContext,
             let llrust_arg = if rust_indirect {
                 llforeign_arg
             } else {
-                builder.load(llforeign_arg)
+                if ty::type_is_bool(rust_ty) {
+                    let tmp = builder.load_range_assert(llforeign_arg, 0, 2, lib::llvm::False);
+                    builder.trunc(tmp, Type::i1(ccx))
+                } else {
+                    builder.load(llforeign_arg)
+                }
             };
 
             debug!("llrust_arg {}{}: {}", "#",
@@ -828,8 +844,8 @@ fn foreign_signature(ccx: &CrateContext, fn_sig: &ty::FnSig, arg_tys: &[ty::t])
      * values by pointer like we do.
      */
 
-    let llarg_tys = arg_tys.iter().map(|&arg| type_of(ccx, arg)).collect();
-    let llret_ty = type_of::type_of(ccx, fn_sig.output);
+    let llarg_tys = arg_tys.iter().map(|&arg| arg_type_of(ccx, arg)).collect();
+    let llret_ty = type_of::arg_type_of(ccx, fn_sig.output);
     LlvmSignature {
         llarg_tys: llarg_tys,
         llret_ty: llret_ty
diff --git a/src/librustc/middle/trans/glue.rs b/src/librustc/middle/trans/glue.rs
index e5e61f38175f..d3552baa7925 100644
--- a/src/librustc/middle/trans/glue.rs
+++ b/src/librustc/middle/trans/glue.rs
@@ -234,7 +234,7 @@ fn trans_struct_drop_flag<'a>(bcx: &'a Block<'a>,
                               -> &'a Block<'a> {
     let repr = adt::represent_type(bcx.ccx(), t);
     let drop_flag = adt::trans_drop_flag_ptr(bcx, &*repr, v0);
-    with_cond(bcx, Load(bcx, drop_flag), |cx| {
+    with_cond(bcx, load_ty(bcx, drop_flag, ty::mk_bool()), |cx| {
         trans_struct_drop(cx, t, v0, dtor_did, class_did, substs)
     })
 }
@@ -505,7 +505,7 @@ fn make_generic_glue(ccx: &CrateContext,
     let bcx = fcx.entry_bcx.borrow().clone().unwrap();
     let llrawptr0 = unsafe { llvm::LLVMGetParam(llfn, fcx.arg_pos(0) as c_uint) };
     let bcx = helper(bcx, llrawptr0, t);
-    finish_fn(&fcx, bcx);
+    finish_fn(&fcx, bcx, ty::mk_nil());
 
     llfn
 }
diff --git a/src/librustc/middle/trans/intrinsic.rs b/src/librustc/middle/trans/intrinsic.rs
index 8e64df8c7d46..c5ce61ed122b 100644
--- a/src/librustc/middle/trans/intrinsic.rs
+++ b/src/librustc/middle/trans/intrinsic.rs
@@ -96,13 +96,19 @@ pub fn trans_intrinsic(ccx: &CrateContext,
         let b = get_param(bcx.fcx.llfn, first_real_arg + 1);
         let llfn = bcx.ccx().get_intrinsic(&name);
 
+        // convert `i1` to a `bool`, and write to the out parameter
         let val = Call(bcx, llfn, [a, b], []);
+        let result = ExtractValue(bcx, val, 0);
+        let overflow = ZExt(bcx, ExtractValue(bcx, val, 1), Type::bool(bcx.ccx()));
+        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);
 
         if type_is_immediate(bcx.ccx(), t) {
-            Ret(bcx, val);
+            Ret(bcx, ret);
         } else {
             let retptr = get_param(bcx.fcx.llfn, bcx.fcx.out_arg_pos());
-            Store(bcx, val, retptr);
+            Store(bcx, ret, retptr);
             RetVoid(bcx);
         }
     }
@@ -367,7 +373,7 @@ pub fn trans_intrinsic(ccx: &CrateContext,
             let retty = *substs.substs.types.get(FnSpace, 0);
             if type_is_immediate(ccx, retty) && !return_type_is_void(ccx, retty) {
                 unsafe {
-                    Ret(bcx, lib::llvm::llvm::LLVMGetUndef(type_of(ccx, retty).to_ref()));
+                    Ret(bcx, lib::llvm::llvm::LLVMGetUndef(arg_type_of(ccx, retty).to_ref()));
                 }
             } else {
                 RetVoid(bcx)
diff --git a/src/librustc/middle/trans/reflect.rs b/src/librustc/middle/trans/reflect.rs
index 91148d31423f..87a730dbc790 100644
--- a/src/librustc/middle/trans/reflect.rs
+++ b/src/librustc/middle/trans/reflect.rs
@@ -331,7 +331,7 @@ impl<'a, 'b> Reflector<'a, 'b> {
                     Some(llreturn) => Br(bcx, llreturn),
                     None => {}
                 };
-                finish_fn(&fcx, bcx);
+                finish_fn(&fcx, bcx, ty::mk_u64());
                 llfdecl
             };
 
diff --git a/src/librustc/middle/trans/type_.rs b/src/librustc/middle/trans/type_.rs
index 1ec792182bd1..b10f6eda8805 100644
--- a/src/librustc/middle/trans/type_.rs
+++ b/src/librustc/middle/trans/type_.rs
@@ -89,7 +89,7 @@ impl Type {
     }
 
     pub fn bool(ccx: &CrateContext) -> Type {
-        Type::i1(ccx)
+        Type::i8(ccx)
     }
 
     pub fn char(ccx: &CrateContext) -> Type {
diff --git a/src/librustc/middle/trans/type_of.rs b/src/librustc/middle/trans/type_of.rs
index c26e11134b60..028722071a69 100644
--- a/src/librustc/middle/trans/type_of.rs
+++ b/src/librustc/middle/trans/type_of.rs
@@ -31,7 +31,7 @@ pub fn return_uses_outptr(ccx: &CrateContext, ty: ty::t) -> bool {
 }
 
 pub fn type_of_explicit_arg(ccx: &CrateContext, arg_ty: ty::t) -> Type {
-    let llty = type_of(ccx, arg_ty);
+    let llty = arg_type_of(ccx, arg_ty);
     if arg_is_indirect(ccx, arg_ty) {
         llty.ptr_to()
     } else {
@@ -46,7 +46,7 @@ pub fn type_of_rust_fn(cx: &CrateContext, has_env: bool,
     // Arg 0: Output pointer.
     // (if the output type is non-immediate)
     let use_out_pointer = return_uses_outptr(cx, output);
-    let lloutputtype = type_of(cx, output);
+    let lloutputtype = arg_type_of(cx, output);
     if use_out_pointer {
         atys.push(lloutputtype.ptr_to());
     }
@@ -167,6 +167,14 @@ pub fn sizing_type_of(cx: &CrateContext, t: ty::t) -> Type {
     llsizingty
 }
 
+pub fn arg_type_of(cx: &CrateContext, t: ty::t) -> Type {
+    if ty::type_is_bool(t) {
+        Type::i1(cx)
+    } else {
+        type_of(cx, t)
+    }
+}
+
 // NB: If you update this, be sure to update `sizing_type_of()` as well.
 pub fn type_of(cx: &CrateContext, t: ty::t) -> Type {
     // Check the cache.