diff --git a/src/librustc/ty/instance.rs b/src/librustc/ty/instance.rs
index 83029df0fe72f..041565c8b5a07 100644
--- a/src/librustc/ty/instance.rs
+++ b/src/librustc/ty/instance.rs
@@ -8,13 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use hir::Unsafety;
 use hir::def_id::DefId;
-use ty::{self, Ty, TypeFoldable, Substs, TyCtxt};
+use ty::{self, Ty, PolyFnSig, TypeFoldable, Substs, TyCtxt};
 use traits;
 use rustc_target::spec::abi::Abi;
 use util::ppaux;
 
 use std::fmt;
+use std::iter;
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub struct Instance<'tcx> {
@@ -59,6 +61,65 @@ impl<'a, 'tcx> Instance<'tcx> {
             &ty,
         )
     }
+
+    fn fn_sig_noadjust(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> PolyFnSig<'tcx> {
+        let ty = self.ty(tcx);
+        match ty.sty {
+            ty::FnDef(..) |
+            // Shims currently have type FnPtr. Not sure this should remain.
+            ty::FnPtr(_) => ty.fn_sig(tcx),
+            ty::Closure(def_id, substs) => {
+                let sig = substs.closure_sig(def_id, tcx);
+
+                let env_ty = tcx.closure_env_ty(def_id, substs).unwrap();
+                sig.map_bound(|sig| tcx.mk_fn_sig(
+                    iter::once(*env_ty.skip_binder()).chain(sig.inputs().iter().cloned()),
+                    sig.output(),
+                    sig.variadic,
+                    sig.unsafety,
+                    sig.abi
+                ))
+            }
+            ty::Generator(def_id, substs, _) => {
+                let sig = substs.poly_sig(def_id, tcx);
+
+                let env_region = ty::ReLateBound(ty::INNERMOST, ty::BrEnv);
+                let env_ty = tcx.mk_mut_ref(tcx.mk_region(env_region), ty);
+
+                sig.map_bound(|sig| {
+                    let state_did = tcx.lang_items().gen_state().unwrap();
+                    let state_adt_ref = tcx.adt_def(state_did);
+                    let state_substs = tcx.intern_substs(&[
+                        sig.yield_ty.into(),
+                        sig.return_ty.into(),
+                    ]);
+                    let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
+
+                    tcx.mk_fn_sig(iter::once(env_ty),
+                        ret_ty,
+                        false,
+                        Unsafety::Normal,
+                        Abi::Rust
+                    )
+                })
+            }
+            _ => bug!("unexpected type {:?} in Instance::fn_sig_noadjust", ty)
+        }
+    }
+
+    pub fn fn_sig(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> ty::PolyFnSig<'tcx> {
+        let mut fn_sig = self.fn_sig_noadjust(tcx);
+        if let InstanceDef::VtableShim(..) = self.def {
+            // Modify fn(self, ...) to fn(self: *mut Self, ...)
+            fn_sig = fn_sig.map_bound(|mut fn_sig| {
+                let mut inputs_and_output = fn_sig.inputs_and_output.to_vec();
+                inputs_and_output[0] = tcx.mk_mut_ptr(inputs_and_output[0]);
+                fn_sig.inputs_and_output = tcx.intern_type_list(&inputs_and_output);
+                fn_sig
+            });
+        }
+        fn_sig
+    }
 }
 
 impl<'tcx> InstanceDef<'tcx> {
diff --git a/src/librustc_codegen_llvm/abi.rs b/src/librustc_codegen_llvm/abi.rs
index 72daa0beb0982..7c7662a88de53 100644
--- a/src/librustc_codegen_llvm/abi.rs
+++ b/src/librustc_codegen_llvm/abi.rs
@@ -11,7 +11,7 @@
 use llvm::{self, AttributePlace};
 use base;
 use builder::{Builder, MemFlags};
-use common::{ty_fn_sig, C_usize};
+use common::C_usize;
 use context::CodegenCx;
 use mir::place::PlaceRef;
 use mir::operand::OperandValue;
@@ -283,8 +283,7 @@ pub trait FnTypeExt<'tcx> {
 
 impl<'tcx> FnTypeExt<'tcx> for FnType<'tcx, Ty<'tcx>> {
     fn of_instance(cx: &CodegenCx<'ll, 'tcx>, instance: &ty::Instance<'tcx>) -> Self {
-        let fn_ty = instance.ty(cx.tcx);
-        let sig = ty_fn_sig(cx, fn_ty);
+        let sig = instance.fn_sig(cx.tcx);
         let sig = cx.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
         FnType::new(cx, sig, &[])
     }
diff --git a/src/librustc_codegen_llvm/base.rs b/src/librustc_codegen_llvm/base.rs
index 501a0b8af76bb..0932ceec9060f 100644
--- a/src/librustc_codegen_llvm/base.rs
+++ b/src/librustc_codegen_llvm/base.rs
@@ -56,7 +56,7 @@ use callee;
 use common::{C_bool, C_bytes_in_context, C_i32, C_usize};
 use rustc_mir::monomorphize::collector::{self, MonoItemCollectionMode};
 use rustc_mir::monomorphize::item::DefPathBasedNames;
-use common::{self, C_struct_in_context, C_array, val_ty};
+use common::{C_struct_in_context, C_array, val_ty};
 use consts;
 use context::CodegenCx;
 use debuginfo;
@@ -491,8 +491,7 @@ pub fn codegen_instance<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, instance: Instance<'
     // release builds.
     info!("codegen_instance({})", instance);
 
-    let fn_ty = instance.ty(cx.tcx);
-    let sig = common::ty_fn_sig_vtable(cx, fn_ty, instance.is_vtable_shim());
+    let sig = instance.fn_sig(cx.tcx);
     let sig = cx.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
 
     let lldecl = cx.instances.borrow().get(&instance).cloned().unwrap_or_else(||
diff --git a/src/librustc_codegen_llvm/callee.rs b/src/librustc_codegen_llvm/callee.rs
index fff0177c94842..7300bac96182b 100644
--- a/src/librustc_codegen_llvm/callee.rs
+++ b/src/librustc_codegen_llvm/callee.rs
@@ -47,16 +47,16 @@ pub fn get_fn(
     assert!(!instance.substs.has_escaping_regions());
     assert!(!instance.substs.has_param_types());
 
-    let fn_ty = instance.ty(cx.tcx);
+    let sig = instance.fn_sig(cx.tcx);
     if let Some(&llfn) = cx.instances.borrow().get(&instance) {
         return llfn;
     }
 
     let sym = tcx.symbol_name(instance).as_str();
-    debug!("get_fn({:?}: {:?}) => {}", instance, fn_ty, sym);
+    debug!("get_fn({:?}: {:?}) => {}", instance, sig, sym);
 
     // Create a fn pointer with the substituted signature.
-    let fn_ptr_ty = tcx.mk_fn_ptr(common::ty_fn_sig_vtable(cx, fn_ty, instance.is_vtable_shim()));
+    let fn_ptr_ty = tcx.mk_fn_ptr(sig);
     let llptrty = cx.layout_of(fn_ptr_ty).llvm_type(cx);
 
     let llfn = if let Some(llfn) = declare::get_declared_value(cx, &sym) {
@@ -91,7 +91,7 @@ pub fn get_fn(
             llfn
         }
     } else {
-        let llfn = declare::declare_fn(cx, &sym, common::ty_fn_sig_vtable(cx, fn_ty, instance.is_vtable_shim()));
+        let llfn = declare::declare_fn(cx, &sym, sig);
         assert_eq!(common::val_ty(llfn), llptrty);
         debug!("get_fn: not casting pointer!");
 
diff --git a/src/librustc_codegen_llvm/common.rs b/src/librustc_codegen_llvm/common.rs
index df91f75837422..c9b464fd8f3dd 100644
--- a/src/librustc_codegen_llvm/common.rs
+++ b/src/librustc_codegen_llvm/common.rs
@@ -30,9 +30,7 @@ use rustc::ty::layout::{HasDataLayout, LayoutOf};
 use rustc::hir;
 
 use libc::{c_uint, c_char};
-use std::iter;
 
-use rustc_target::spec::abi::Abi;
 use syntax::symbol::LocalInternedString;
 use syntax_pos::{Span, DUMMY_SP};
 
@@ -404,71 +402,3 @@ pub fn shift_mask_val(
         _ => bug!("shift_mask_val: expected Integer or Vector, found {:?}", kind),
     }
 }
-
-pub fn ty_fn_sig<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
-                           ty: Ty<'tcx>)
-                           -> ty::PolyFnSig<'tcx>
-{
-    match ty.sty {
-        ty::FnDef(..) |
-        // Shims currently have type FnPtr. Not sure this should remain.
-        ty::FnPtr(_) => ty.fn_sig(cx.tcx),
-        ty::Closure(def_id, substs) => {
-            let tcx = cx.tcx;
-            let sig = substs.closure_sig(def_id, tcx);
-
-            let env_ty = tcx.closure_env_ty(def_id, substs).unwrap();
-            sig.map_bound(|sig| tcx.mk_fn_sig(
-                iter::once(*env_ty.skip_binder()).chain(sig.inputs().iter().cloned()),
-                sig.output(),
-                sig.variadic,
-                sig.unsafety,
-                sig.abi
-            ))
-        }
-        ty::Generator(def_id, substs, _) => {
-            let tcx = cx.tcx;
-            let sig = substs.poly_sig(def_id, cx.tcx);
-
-            let env_region = ty::ReLateBound(ty::INNERMOST, ty::BrEnv);
-            let env_ty = tcx.mk_mut_ref(tcx.mk_region(env_region), ty);
-
-            sig.map_bound(|sig| {
-                let state_did = tcx.lang_items().gen_state().unwrap();
-                let state_adt_ref = tcx.adt_def(state_did);
-                let state_substs = tcx.intern_substs(&[
-                    sig.yield_ty.into(),
-                    sig.return_ty.into(),
-                ]);
-                let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
-
-                tcx.mk_fn_sig(iter::once(env_ty),
-                    ret_ty,
-                    false,
-                    hir::Unsafety::Normal,
-                    Abi::Rust
-                )
-            })
-        }
-        _ => bug!("unexpected type {:?} to ty_fn_sig", ty)
-    }
-}
-
-pub fn ty_fn_sig_vtable<'a, 'tcx>(
-    cx: &CodegenCx<'a, 'tcx>,
-    ty: Ty<'tcx>,
-    is_vtable_shim: bool
-    ) -> ty::PolyFnSig<'tcx>
-{
-    let mut fn_sig = ty_fn_sig(cx, ty);
-    if is_vtable_shim {
-        // Modify fn(self, ...) to fn(self: *mut Self, ...)
-        fn_sig = fn_sig.map_bound(|mut fn_sig| {
-            let mut inputs_and_output = fn_sig.inputs_and_output.to_vec();
-            inputs_and_output[0] = cx.tcx.mk_mut_ptr(inputs_and_output[0]);
-            fn_sig.inputs_and_output = cx.tcx.intern_type_list(&inputs_and_output);
-            fn_sig
-        });
-    }
-    fn_sig
-}
diff --git a/src/librustc_codegen_llvm/mir/block.rs b/src/librustc_codegen_llvm/mir/block.rs
index 9fab362f7e2ff..d98b7869ae98e 100644
--- a/src/librustc_codegen_llvm/mir/block.rs
+++ b/src/librustc_codegen_llvm/mir/block.rs
@@ -298,8 +298,7 @@ impl FunctionCx<'a, 'll, 'tcx> {
                 };
                 let (drop_fn, fn_ty) = match ty.sty {
                     ty::Dynamic(..) => {
-                        let fn_ty = drop_fn.ty(bx.cx.tcx);
-                        let sig = common::ty_fn_sig(bx.cx, fn_ty);
+                        let sig = drop_fn.fn_sig(bx.cx.tcx);
                         let sig = bx.tcx().normalize_erasing_late_bound_regions(
                             ty::ParamEnv::reveal_all(),
                             &sig,
diff --git a/src/librustc_codegen_llvm/mono_item.rs b/src/librustc_codegen_llvm/mono_item.rs
index d160f114d4ccd..91c1ccbe00213 100644
--- a/src/librustc_codegen_llvm/mono_item.rs
+++ b/src/librustc_codegen_llvm/mono_item.rs
@@ -17,7 +17,6 @@
 use asm;
 use attributes;
 use base;
-use common;
 use consts;
 use context::CodegenCx;
 use declare;
@@ -154,8 +153,7 @@ fn predefine_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
     assert!(!instance.substs.needs_infer() &&
             !instance.substs.has_param_types());
 
-    let mono_ty = instance.ty(cx.tcx);
-    let mono_sig = common::ty_fn_sig_vtable(cx, mono_ty, instance.is_vtable_shim());
+    let mono_sig = instance.fn_sig(cx.tcx);
     let attrs = cx.tcx.codegen_fn_attrs(instance.def_id());
     let lldecl = declare::declare_fn(cx, symbol_name, mono_sig);
     unsafe { llvm::LLVMRustSetLinkage(lldecl, base::linkage_to_llvm(linkage)) };
@@ -180,7 +178,7 @@ fn predefine_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
         }
     }
 
-    debug!("predefine_fn: mono_ty = {:?} instance = {:?}", mono_ty, instance);
+    debug!("predefine_fn: mono_sig = {:?} instance = {:?}", mono_sig, instance);
     if instance.def.is_inline(cx.tcx) {
         attributes::inline(cx, lldecl, attributes::InlineAttr::Hint);
     }