diff --git a/src/librustc_mir/interpret/intern.rs b/src/librustc_mir/interpret/intern.rs
index f3c503b2970a..630f3f603449 100644
--- a/src/librustc_mir/interpret/intern.rs
+++ b/src/librustc_mir/interpret/intern.rs
@@ -15,9 +15,8 @@ use super::{
     AllocId, Allocation, InterpCx, Machine, MemoryKind, MPlaceTy, Scalar, ValueVisitor,
 };
 
-struct InternVisitor<'rt, 'mir, 'tcx, M>
-where
-    M: Machine<
+pub trait CompileTimeMachine<'mir, 'tcx> =
+    Machine<
         'mir,
         'tcx,
         MemoryKinds = !,
@@ -27,8 +26,9 @@ where
         MemoryExtra = (),
         AllocExtra = (),
         MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>,
-    >,
-{
+    >;
+
+struct InternVisitor<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx>> {
     /// The ectx from which we intern.
     ecx: &'rt mut InterpCx<'mir, 'tcx, M>,
     /// Previously encountered safe references.
@@ -70,27 +70,14 @@ struct IsStaticOrFn;
 /// `immutable` things might become mutable if `ty` is not frozen.
 /// `ty` can be `None` if there is no potential interior mutability
 /// to account for (e.g. for vtables).
-fn intern_shallow<'rt, 'mir, 'tcx, M>(
+fn intern_shallow<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx>>(
     ecx: &'rt mut InterpCx<'mir, 'tcx, M>,
     leftover_allocations: &'rt mut FxHashSet<AllocId>,
     mode: InternMode,
     alloc_id: AllocId,
     mutability: Mutability,
     ty: Option<Ty<'tcx>>,
-) -> InterpResult<'tcx, Option<IsStaticOrFn>>
-where
-    M: Machine<
-        'mir,
-        'tcx,
-        MemoryKinds = !,
-        PointerTag = (),
-        ExtraFnVal = !,
-        FrameExtra = (),
-        MemoryExtra = (),
-        AllocExtra = (),
-        MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>,
-    >,
-{
+) -> InterpResult<'tcx, Option<IsStaticOrFn>> {
     trace!("InternVisitor::intern {:?} with {:?}", alloc_id, mutability,);
     // remove allocation
     let tcx = ecx.tcx;
@@ -152,20 +139,7 @@ where
     Ok(None)
 }
 
-impl<'rt, 'mir, 'tcx, M> InternVisitor<'rt, 'mir, 'tcx, M>
-where
-    M: Machine<
-        'mir,
-        'tcx,
-        MemoryKinds = !,
-        PointerTag = (),
-        ExtraFnVal = !,
-        FrameExtra = (),
-        MemoryExtra = (),
-        AllocExtra = (),
-        MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>,
-    >,
-{
+impl<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx>> InternVisitor<'rt, 'mir, 'tcx, M> {
     fn intern_shallow(
         &mut self,
         alloc_id: AllocId,
@@ -183,22 +157,10 @@ where
     }
 }
 
-impl<'rt, 'mir, 'tcx, M>
+impl<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx>>
     ValueVisitor<'mir, 'tcx, M>
 for
     InternVisitor<'rt, 'mir, 'tcx, M>
-where
-    M: Machine<
-        'mir,
-        'tcx,
-        MemoryKinds = !,
-        PointerTag = (),
-        ExtraFnVal = !,
-        FrameExtra = (),
-        MemoryExtra = (),
-        AllocExtra = (),
-        MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>,
-    >,
 {
     type V = MPlaceTy<'tcx>;
 
@@ -312,25 +274,12 @@ where
     }
 }
 
-pub fn intern_const_alloc_recursive<M>(
+pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx>>(
     ecx: &mut InterpCx<'mir, 'tcx, M>,
     // The `mutability` of the place, ignoring the type.
     place_mut: Option<hir::Mutability>,
     ret: MPlaceTy<'tcx>,
-) -> InterpResult<'tcx>
-where
-    M: Machine<
-        'mir,
-        'tcx,
-        MemoryKinds = !,
-        PointerTag = (),
-        ExtraFnVal = !,
-        FrameExtra = (),
-        MemoryExtra = (),
-        AllocExtra = (),
-        MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>,
-    >,
-{
+) -> InterpResult<'tcx> {
     let tcx = ecx.tcx;
     let (base_mutability, base_intern_mode) = match place_mut {
         Some(hir::Mutability::Immutable) => (Mutability::Immutable, InternMode::Static),
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
index 6d19cd63bc32..b5273ea7bc60 100644
--- a/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@ -27,6 +27,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![feature(range_is_empty)]
 #![feature(stmt_expr_attributes)]
 #![feature(bool_to_option)]
+#![feature(trait_alias)]
 
 #![recursion_limit="256"]
 
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index f7572f366842..58d1a8b70979 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -649,31 +649,28 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     }
 
     fn should_const_prop(&mut self, op: OpTy<'tcx>) -> bool {
-        if self.tcx.sess.opts.debugging_opts.mir_opt_level == 0 {
+        let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level;
+
+        if mir_opt_level == 0 {
             return false;
         }
 
-        let is_scalar = match *op {
+        match *op {
             interpret::Operand::Immediate(Immediate::Scalar(ScalarMaybeUndef::Scalar(s))) =>
                 s.is_bits(),
             interpret::Operand::Immediate(Immediate::ScalarPair(ScalarMaybeUndef::Scalar(l),
                                                                 ScalarMaybeUndef::Scalar(r))) =>
                 l.is_bits() && r.is_bits(),
-            _ => false
-        };
-
-        if let interpret::Operand::Indirect(_) = *op {
-            if self.tcx.sess.opts.debugging_opts.mir_opt_level >= 2 {
+            interpret::Operand::Indirect(_) if mir_opt_level >= 2 => {
                 intern_const_alloc_recursive(
                     &mut self.ecx,
                     None,
                     op.assert_mem_place()
                 ).expect("failed to intern alloc");
-                return true;
-            }
+                true
+            },
+            _ => false
         }
-
-        return is_scalar;
     }
 }