diff --git a/src/rustc/middle/trans/native.rs b/src/rustc/middle/trans/native.rs
index ba2c60a6bc9b5..031d0b3a86f67 100644
--- a/src/rustc/middle/trans/native.rs
+++ b/src/rustc/middle/trans/native.rs
@@ -1,8 +1,11 @@
-import driver::session::session;
+import driver::session::{session, arch_x86_64};
 import syntax::codemap::span;
-import ctypes::c_uint;
+import ctypes::{ c_uint, unsigned };
 import front::attr;
-import lib::llvm::{ llvm, TypeRef, ValueRef };
+import lib::llvm::{ llvm, TypeRef, ValueRef,
+                    ModuleRef, CallConv, Attribute,
+                    StructRetAttribute, ByValAttribute
+                  };
 import syntax::ast;
 import back::link;
 import common::*;
@@ -14,6 +17,381 @@ import std::map::hashmap;
 export link_name, trans_native_mod, register_crust_fn, trans_crust_fn,
        decl_native_fn;
 
+enum x86_64_reg_class {
+    no_class,
+    integer_class,
+    sse_fs_class,
+    sse_fv_class,
+    sse_ds_class,
+    sse_dv_class,
+    sse_int_class,
+    sseup_class,
+    x87_class,
+    x87up_class,
+    complex_x87_class,
+    memory_class
+}
+
+fn is_sse(c: x86_64_reg_class) -> bool {
+    ret alt c {
+        sse_fs_class | sse_fv_class |
+        sse_ds_class | sse_dv_class { true }
+        _ { false }
+    };
+}
+
+fn is_ymm(cls: [x86_64_reg_class]) -> bool {
+    let len = vec::len(cls);
+    ret (len > 2u &&
+         is_sse(cls[0]) &&
+         cls[1] == sseup_class &&
+         cls[2] == sseup_class) ||
+        (len > 3u &&
+         is_sse(cls[1]) &&
+         cls[2] == sseup_class &&
+         cls[3] == sseup_class);
+}
+
+fn classify_ty(ty: TypeRef) -> [x86_64_reg_class] {
+    fn align(off: uint, ty: TypeRef) -> uint {
+        let a = ty_align(ty);
+        ret (off + a - 1u) / a * a;
+    }
+
+    fn struct_tys(ty: TypeRef) -> [TypeRef] {
+        let n = llvm::LLVMCountStructElementTypes(ty);
+        let elts = vec::init_elt(n as uint, ptr::null());
+        vec::as_buf(elts) {|buf|
+            llvm::LLVMGetStructElementTypes(ty, buf);
+        }
+        ret elts;
+    }
+
+    fn ty_align(ty: TypeRef) -> uint {
+        ret alt llvm::LLVMGetTypeKind(ty) as int {
+            8 /* integer */ {
+                ((llvm::LLVMGetIntTypeWidth(ty) as uint) + 7u) / 8u
+            }
+            12 /* pointer */ { 8u }
+            2 /* float */ { 4u }
+            3 /* double */ { 8u }
+            10 /* struct */ {
+                vec::foldl(0u, struct_tys(ty)) {|a, t|
+                    uint::max(a, ty_align(t))
+                }
+            }
+            _ {
+                fail "ty_size: unhandled type"
+            }
+        };
+    }
+
+    fn ty_size(ty: TypeRef) -> uint {
+        ret alt llvm::LLVMGetTypeKind(ty) as int {
+            8 /* integer */ {
+                ((llvm::LLVMGetIntTypeWidth(ty) as uint) + 7u) / 8u
+            }
+            12 /* pointer */ { 8u }
+            2 /* float */ { 4u }
+            3 /* double */ { 8u }
+            10 /* struct */ {
+                vec::foldl(0u, struct_tys(ty)) {|s, t|
+                    s + ty_size(t)
+                }
+            }
+            _ {
+                fail "ty_size: unhandled type"
+            }
+        };
+    }
+
+    fn all_mem(cls: [mut x86_64_reg_class]) {
+        vec::iteri(cls) {|i, _c|
+            cls[i] = memory_class;
+        }
+    }
+
+    fn unify(cls: [mut x86_64_reg_class], i: uint,
+             new: x86_64_reg_class) {
+        if cls[i] == new {
+            ret;
+        } else if cls[i] == no_class {
+            cls[i] = new;
+        } else if new == no_class {
+            ret;
+        } else if cls[i] == memory_class || new == memory_class {
+            cls[i] = memory_class;
+        } else if cls[i] == integer_class || new == integer_class {
+            cls[i] = integer_class;
+        } else if cls[i] == x87_class ||
+                  cls[i] == x87up_class ||
+                  cls[i] == complex_x87_class ||
+                  new == x87_class ||
+                  new == x87up_class ||
+                  new == complex_x87_class {
+            cls[i] = memory_class;
+        } else {
+            cls[i] = new;
+        }
+    }
+
+    fn classify_struct(tys: [TypeRef],
+                       cls: [mut x86_64_reg_class], i: uint,
+                       off: uint) {
+        if vec::is_empty(tys) {
+            classify(T_i64(), cls, i, off);
+        } else {
+            let field_off = off;
+            for ty in tys {
+                field_off = align(field_off, ty);
+                classify(ty, cls, i, field_off);
+                field_off += ty_size(ty);
+            }
+        }
+    }
+
+    fn classify(ty: TypeRef,
+                cls: [mut x86_64_reg_class], i: uint,
+                off: uint) {
+        let t_align = ty_align(ty);
+        let t_size = ty_size(ty);
+
+        let misalign = off % t_align;
+        if misalign != 0u {
+            let i = off / 8u;
+            let e = (off + t_size + 7u) / 8u;
+            while i < e {
+                unify(cls, i, memory_class);
+                i += 1u;
+            }
+            ret;
+        }
+
+        alt llvm::LLVMGetTypeKind(ty) as int {
+            8 /* integer */ |
+            12 /* pointer */ {
+                unify(cls, off / 8u, integer_class);
+            }
+            2 /* float */ {
+                if off % 8u == 4u {
+                    unify(cls, off / 8u, sse_fv_class);
+                } else {
+                    unify(cls, off / 8u, sse_fs_class);
+                }
+            }
+            3 /* double */ {
+                unify(cls, off / 8u, sse_ds_class);
+            }
+            10 /* struct */ {
+                classify_struct(struct_tys(ty), cls, i, off);
+            }
+            _ {
+                fail "classify: unhandled type";
+            }
+        }
+    }
+
+    fn fixup(ty: TypeRef, cls: [mut x86_64_reg_class]) {
+        let i = 0u;
+        let e = vec::len(cls);
+        if vec::len(cls) > 2u &&
+           llvm::LLVMGetTypeKind(ty) as int == 10 /* struct */ {
+            if is_sse(cls[i]) {
+                i += 1u;
+                while i < e {
+                    if cls[i] != sseup_class {
+                        all_mem(cls);
+                        ret;
+                    }
+                    i += 1u;
+                }
+            } else {
+                all_mem(cls);
+                ret
+            }
+        } else {
+            while i < e {
+                if cls[i] == memory_class {
+                    all_mem(cls);
+                    ret;
+                }
+                if cls[i] == x87up_class {
+                    // for darwin
+                    // cls[i] = sse_ds_class;
+                    all_mem(cls);
+                    ret;
+                }
+                if cls[i] == sseup_class {
+                    cls[i] = sse_int_class;
+                } else if is_sse(cls[i]) {
+                    i += 1u;
+                    while cls[i] == sseup_class { i += 1u; }
+                } else if cls[i] == x87_class {
+                    i += 1u;
+                    while cls[i] == x87up_class { i += 1u; }
+                } else {
+                    i += 1u;
+                }
+            }
+        }
+    }
+
+    let words = (ty_size(ty) + 7u) / 8u;
+    let cls = vec::to_mut(vec::init_elt(words, no_class));
+    if words > 4u {
+        all_mem(cls);
+        ret vec::from_mut(cls);
+    }
+    classify(ty, cls, 0u, 0u);
+    fixup(ty, cls);
+    ret vec::from_mut(cls);
+}
+
+fn llreg_ty(cls: [x86_64_reg_class]) -> TypeRef {
+    fn llvec_len(cls: [x86_64_reg_class]) -> uint {
+        let len = 1u;
+        for c in cls {
+            if c != sseup_class {
+                break;
+            }
+            len += 1u;
+        }
+        ret len;
+    }
+
+    let tys = [];
+    let i = 0u;
+    let e = vec::len(cls);
+    while i < e {
+        alt cls[i] {
+            integer_class {
+                tys += [T_i64()];
+            }
+            sse_fv_class {
+                let vec_len = llvec_len(vec::tailn(cls, i + 1u)) * 2u;
+                let vec_ty = llvm::LLVMVectorType(T_f32(),
+                                                  vec_len as unsigned);
+                tys += [vec_ty];
+                i += vec_len;
+                cont;
+            }
+            sse_fs_class {
+                tys += [T_f32()];
+            }
+            sse_ds_class {
+                tys += [T_f64()];
+            }
+            _ {
+                fail "llregtype: unhandled class";
+            }
+        }
+        i += 1u;
+    }
+    ret T_struct(tys);
+}
+
+type x86_64_llty = {
+    cast: bool,
+    ty: TypeRef
+};
+
+type x86_64_tys = {
+    arg_tys: [x86_64_llty],
+    ret_ty: x86_64_llty,
+    attrs: [option::t<Attribute>],
+    sret: bool
+};
+
+fn x86_64_tys(atys: [TypeRef],
+              rty: TypeRef,
+              ret_def: bool) -> x86_64_tys {
+    fn is_reg_ty(ty: TypeRef) -> bool {
+        ret alt llvm::LLVMGetTypeKind(ty) as int {
+            8 /* integer */ |
+            12 /* pointer */ |
+            2 /* float */ |
+            3 /* double */ { true }
+            _ { false }
+        };
+    }
+
+    fn is_pass_byval(cls: [x86_64_reg_class]) -> bool {
+        ret cls[0] == memory_class ||
+            cls[0] == x87_class ||
+            cls[0] == complex_x87_class;
+    }
+
+    fn is_ret_bysret(cls: [x86_64_reg_class]) -> bool {
+        ret cls[0] == memory_class;
+    }
+
+    fn x86_64_ty(ty: TypeRef,
+                 is_mem_cls: fn(cls: [x86_64_reg_class]) -> bool,
+                 attr: Attribute) -> (x86_64_llty, option::t<Attribute>) {
+        let cast = false;
+        let ty_attr = option::none;
+        let llty = ty;
+        if !is_reg_ty(ty) {
+            let cls = classify_ty(ty);
+            if is_mem_cls(cls) {
+                llty = T_ptr(ty);
+                ty_attr = option::some(attr);
+            } else {
+                cast = true;
+                llty = llreg_ty(cls);
+            }
+        }
+        ret ({ cast: cast, ty: llty }, ty_attr);
+    }
+
+    let arg_tys = [];
+    let attrs = [];
+    for t in atys {
+        let (ty, attr) = x86_64_ty(t, is_pass_byval, ByValAttribute);
+        arg_tys += [ty];
+        attrs += [attr];
+    }
+    let (ret_ty, ret_attr) = x86_64_ty(rty, is_ret_bysret,
+                                            StructRetAttribute);
+    let sret = option::is_some(ret_attr);
+    if sret {
+        arg_tys = [ret_ty] + arg_tys;
+        ret_ty = { cast:  false,
+                   ty: T_void()
+                 };
+        attrs = [ret_attr] + attrs;
+    } else if !ret_def {
+        ret_ty = { cast: false,
+                   ty: T_void()
+                 };
+    }
+    ret {
+        arg_tys: arg_tys,
+        ret_ty: ret_ty,
+        attrs: attrs,
+        sret: sret
+    };
+}
+
+fn decl_x86_64_fn(tys: x86_64_tys,
+                  decl: fn(fnty: TypeRef) -> ValueRef) -> ValueRef {
+    let atys = vec::map(tys.arg_tys) {|t| t.ty };
+    let rty = tys.ret_ty.ty;
+    let fnty = T_fn(atys, rty);
+    let llfn = decl(fnty);
+
+    vec::iteri(tys.attrs) {|i, a|
+        alt a {
+            option::some(attr) {
+                let llarg = llvm::LLVMGetParam(llfn, i as unsigned);
+                llvm::LLVMAddAttribute(llarg, attr as unsigned);
+            }
+            _ {}
+        }
+    }
+    ret llfn;
+}
+
 fn link_name(i: @ast::native_item) -> str {
     alt attr::get_meta_item_value_str_by_name(i.attrs, "link_name") {
       none { ret i.ident; }
@@ -26,7 +404,8 @@ type c_stack_tys = {
     ret_ty: TypeRef,
     ret_def: bool,
     bundle_ty: TypeRef,
-    shim_fn_ty: TypeRef
+    shim_fn_ty: TypeRef,
+    x86_64_tys: option::t<x86_64_tys>
 };
 
 fn c_arg_and_ret_lltys(ccx: crate_ctxt,
@@ -45,12 +424,19 @@ fn c_stack_tys(ccx: crate_ctxt,
                id: ast::node_id) -> @c_stack_tys {
     let (llargtys, llretty, ret_ty) = c_arg_and_ret_lltys(ccx, id);
     let bundle_ty = T_struct(llargtys + [T_ptr(llretty)]);
+    let ret_def = !ty::type_is_bot(ret_ty) && !ty::type_is_nil(ret_ty);
+    let x86_64 = if ccx.sess.targ_cfg.arch == arch_x86_64 {
+        option::some(x86_64_tys(llargtys, llretty, ret_def))
+    } else {
+        option::none
+    };
     ret @{
         arg_tys: llargtys,
         ret_ty: llretty,
-        ret_def: !ty::type_is_bot(ret_ty) && !ty::type_is_nil(ret_ty),
+        ret_def: ret_def,
         bundle_ty: bundle_ty,
-        shim_fn_ty: T_fn([T_ptr(bundle_ty)], T_void())
+        shim_fn_ty: T_fn([T_ptr(bundle_ty)], T_void()),
+        x86_64_tys: x86_64
     };
 }
 
@@ -173,31 +559,101 @@ fn trans_native_mod(ccx: crate_ctxt,
             let llargvals = [];
             let i = 0u;
             let n = vec::len(tys.arg_tys);
-            while i < n {
-                let llargval = load_inbounds(bcx, llargbundle, [0, i as int]);
-                llargvals += [llargval];
-                i += 1u;
+
+            alt tys.x86_64_tys {
+                some(x86_64) {
+                    let atys = x86_64.arg_tys;
+                    let attrs = x86_64.attrs;
+                    if x86_64.sret {
+                        let llretptr = GEPi(bcx, llargbundle, [0, n as int]);
+                        let llretloc = Load(bcx, llretptr);
+                        llargvals = [llretloc];
+                        atys = vec::tail(atys);
+                        attrs = vec::tail(attrs);
+                    }
+                    while i < n {
+                        let llargval = if atys[i].cast {
+                            let arg_ptr = GEPi(bcx, llargbundle,
+                                                    [0, i as int]);
+                            arg_ptr = BitCast(bcx, arg_ptr,
+                                                   T_ptr(atys[i].ty));
+                            Load(bcx, arg_ptr)
+                        } else if option::is_some(attrs[i]) {
+                            GEPi(bcx, llargbundle, [0, i as int])
+                        } else {
+                            load_inbounds(bcx, llargbundle, [0, i as int])
+                        };
+                        llargvals += [llargval];
+                        i += 1u;
+                    }
+                }
+                _ {
+                    while i < n {
+                        let llargval = load_inbounds(bcx, llargbundle,
+                                                          [0, i as int]);
+                        llargvals += [llargval];
+                        i += 1u;
+                    }
+                }
             }
             ret llargvals;
         }
 
         fn build_ret(bcx: block, tys: @c_stack_tys,
                      llargbundle: ValueRef, llretval: ValueRef)  {
-            if tys.ret_def {
-                let n = vec::len(tys.arg_tys);
-                // R** llretptr = &args->r;
-                let llretptr = GEPi(bcx, llargbundle, [0, n as int]);
-                // R* llretloc = *llretptr; /* (args->r) */
-                let llretloc = Load(bcx, llretptr);
-                // *args->r = r;
-                Store(bcx, llretval, llretloc);
+            alt tys.x86_64_tys {
+                some(x86_64) {
+                    vec::iteri(x86_64.attrs) {|i, a|
+                        alt a {
+                            some(attr) {
+                                llvm::LLVMAddInstrAttribute(
+                                    llretval, (i + 1u) as unsigned,
+                                              attr as unsigned);
+                            }
+                            _ {}
+                        }
+                    }
+                    if x86_64.sret || !tys.ret_def {
+                        ret;
+                    }
+                    let n = vec::len(tys.arg_tys);
+                    let llretptr = GEPi(bcx, llargbundle, [0, n as int]);
+                    let llretloc = Load(bcx, llretptr);
+                    if x86_64.ret_ty.cast {
+                        let tmp_ptr = BitCast(bcx, llretloc,
+                                                   T_ptr(x86_64.ret_ty.ty));
+                        Store(bcx, llretval, tmp_ptr);
+                    } else {
+                        Store(bcx, llretval, llretloc);
+                    };
+                }
+                _ {
+                    if tys.ret_def {
+                        let n = vec::len(tys.arg_tys);
+                        // R** llretptr = &args->r;
+                        let llretptr = GEPi(bcx, llargbundle, [0, n as int]);
+                        // R* llretloc = *llretptr; /* (args->r) */
+                        let llretloc = Load(bcx, llretptr);
+                        // *args->r = r;
+                        Store(bcx, llretval, llretloc);
+                    }
+                }
             }
         }
 
         let lname = link_name(native_item);
         // Declare the "prototype" for the base function F:
-        let llbasefnty = T_fn(tys.arg_tys, tys.ret_ty);
-        let llbasefn = decl_fn(ccx.llmod, lname, cc, llbasefnty);
+        let llbasefn = alt tys.x86_64_tys {
+            some(x86_64) {
+                decl_x86_64_fn(x86_64) {|fnty|
+                    decl_fn(ccx.llmod, lname, cc, fnty)
+                }
+            }
+            _ {
+                let llbasefnty = T_fn(tys.arg_tys, tys.ret_ty);
+                decl_fn(ccx.llmod, lname, cc, llbasefnty)
+            }
+        };
         // Name the shim function
         let shim_name = lname + "__c_stack_shim";
         ret build_shim_fn_(ccx, shim_name, llbasefn, tys, cc,
@@ -314,23 +770,87 @@ fn trans_crust_fn(ccx: crate_ctxt, path: ast_map::path, decl: ast::fn_decl,
 
         fn build_args(bcx: block, tys: @c_stack_tys,
                       llwrapfn: ValueRef, llargbundle: ValueRef) {
-            let llretptr = alloca(bcx, tys.ret_ty);
-            let i = 0u, n = vec::len(tys.arg_tys);
-            while i < n {
-                let llargval = llvm::LLVMGetParam(
-                    llwrapfn, i as c_uint);
-                store_inbounds(bcx, llargval, llargbundle, [0, i as int]);
-                i += 1u;
+            alt tys.x86_64_tys {
+                option::some(x86_64) {
+                    let atys = x86_64.arg_tys;
+                    let attrs = x86_64.attrs;
+                    let j = 0u;
+                    let llretptr = if x86_64.sret {
+                        atys = vec::tail(atys);
+                        attrs = vec::tail(attrs);
+                        j = 1u;
+                        llvm::LLVMGetParam(llwrapfn, 0 as c_uint)
+                    } else if x86_64.ret_ty.cast {
+                        let retptr = alloca(bcx, x86_64.ret_ty.ty);
+                        BitCast(bcx, retptr, T_ptr(tys.ret_ty))
+                    } else {
+                        alloca(bcx, tys.ret_ty)
+                    };
+
+                    let i = 0u, n = vec::len(atys);
+                    while i < n {
+                        let argval = llvm::LLVMGetParam(llwrapfn,
+                                                        (i + j) as c_uint);
+                        if option::is_some(attrs[i]) {
+                            argval = Load(bcx, argval);
+                            store_inbounds(bcx, argval, llargbundle,
+                                                        [0, i as int]);
+                        } else if atys[i].cast {
+                            let argptr = GEPi(bcx, llargbundle,
+                                                   [0, i as int]);
+                            argptr = BitCast(bcx, argptr, T_ptr(atys[i].ty));
+                            Store(bcx, argval, argptr);
+                        } else {
+                            store_inbounds(bcx, argval, llargbundle,
+                                                        [0, i as int]);
+                        }
+                        i += 1u;
+                    }
+                    store_inbounds(bcx, llretptr, llargbundle, [0, n as int]);
+                }
+                _ {
+                    let llretptr = alloca(bcx, tys.ret_ty);
+                    let i = 0u, n = vec::len(tys.arg_tys);
+                    while i < n {
+                        let llargval = llvm::LLVMGetParam(llwrapfn,
+                                                          i as c_uint);
+                        store_inbounds(bcx, llargval, llargbundle,
+                                                      [0, i as int]);
+                        i += 1u;
+                    }
+                    store_inbounds(bcx, llretptr, llargbundle, [0, n as int]);
+                }
             }
-            store_inbounds(bcx, llretptr, llargbundle, [0, n as int]);
         }
 
         fn build_ret(bcx: block, tys: @c_stack_tys,
                      llargbundle: ValueRef) {
-            let n = vec::len(tys.arg_tys);
-            let llretval = load_inbounds(bcx, llargbundle, [0, n as int]);
-            let llretval = Load(bcx, llretval);
-            Ret(bcx, llretval);
+            alt tys.x86_64_tys {
+                option::some(x86_64) {
+                    if x86_64.sret || !tys.ret_def {
+                        RetVoid(bcx);
+                        ret;
+                    }
+                    let n = vec::len(tys.arg_tys);
+                    let llretval = load_inbounds(bcx, llargbundle,
+                                                      [0, n as int]);
+                    let llretval = if x86_64.ret_ty.cast {
+                        let retptr = BitCast(bcx, llretval,
+                                                  T_ptr(x86_64.ret_ty.ty));
+                        Load(bcx, retptr)
+                    } else {
+                        Load(bcx, llretval)
+                    };
+                    Ret(bcx, llretval);
+                }
+                _ {
+                    let n = vec::len(tys.arg_tys);
+                    let llretval = load_inbounds(bcx, llargbundle,
+                                                      [0, n as int]);
+                    let llretval = Load(bcx, llretval);
+                    Ret(bcx, llretval);
+                }
+            }
         }
 
         build_wrap_fn_(ccx, tys, llshimfn, llwrapfn,
@@ -351,10 +871,19 @@ fn register_crust_fn(ccx: crate_ctxt, sp: span,
                      path: ast_map::path, node_id: ast::node_id)
     -> ValueRef {
     let t = ty::node_id_to_type(ccx.tcx, node_id);
-    let (llargtys, llretty, _) = c_arg_and_ret_lltys(ccx, node_id);
-    let llfty = T_fn(llargtys, llretty);
-    register_fn_fuller(ccx, sp, path, "crust fn", node_id,
-                       t, lib::llvm::CCallConv, llfty)
+    let (llargtys, llretty, ret_ty) = c_arg_and_ret_lltys(ccx, node_id);
+    ret if ccx.sess.targ_cfg.arch == arch_x86_64 {
+        let ret_def = !ty::type_is_bot(ret_ty) && !ty::type_is_nil(ret_ty);
+        let x86_64 = x86_64_tys(llargtys, llretty, ret_def);
+        decl_x86_64_fn(x86_64) {|fnty|
+            register_fn_fuller(ccx, sp, path, "crust fn", node_id,
+                               t, lib::llvm::CCallConv, fnty)
+        }
+    } else {
+        let llfty = T_fn(llargtys, llretty);
+        register_fn_fuller(ccx, sp, path, "crust fn", node_id,
+                           t, lib::llvm::CCallConv, llfty)
+    }
 }
 
 fn abi_of_native_fn(ccx: crate_ctxt, i: @ast::native_item)