diff --git a/src/librustc/mir/cache.rs b/src/librustc/mir/cache.rs
new file mode 100644
index 00000000000..8dac356c0a2
--- /dev/null
+++ b/src/librustc/mir/cache.rs
@@ -0,0 +1,47 @@
+use rustc_index::vec::IndexVec;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_serialize::{Encodable, Encoder, Decodable, Decoder};
+use crate::ich::StableHashingContext;
+use crate::mir::BasicBlock;
+
+#[derive(Clone, Debug)]
+pub(in crate::mir) struct Cache {
+    pub(in crate::mir) predecessors: Option<IndexVec<BasicBlock, Vec<BasicBlock>>>
+}
+
+
+impl rustc_serialize::Encodable for Cache {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        Encodable::encode(&(), s)
+    }
+}
+
+impl rustc_serialize::Decodable for Cache {
+    fn decode<D: Decoder>(d: &mut D) -> Result<Self, D::Error> {
+        Decodable::decode(d).map(|_v: ()| Self::new())
+    }
+}
+
+impl<'a> HashStable<StableHashingContext<'a>> for Cache {
+    fn hash_stable(&self, _: &mut StableHashingContext<'a>, _: &mut StableHasher) {
+        // Do nothing.
+    }
+}
+
+impl Cache {
+    pub fn new() -> Self {
+        Cache {
+            predecessors: None
+        }
+    }
+
+    #[inline]
+    pub fn invalidate_predecessors(&mut self) {
+        // FIXME: consider being more fine-grained
+        self.predecessors = None;
+    }
+}
+
+CloneTypeFoldableAndLiftImpls! {
+    Cache,
+}
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index ea9de2fdae8..fb5ee211de2 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -40,6 +40,7 @@ use syntax_pos::{Span, DUMMY_SP};
 
 pub use crate::mir::interpret::AssertMessage;
 
+mod cache;
 pub mod interpret;
 pub mod mono;
 pub mod tcx;
@@ -154,7 +155,7 @@ pub struct Body<'tcx> {
     pub span: Span,
 
     /// A cache for various calculations.
-    predecessors_cache: Option<IndexVec<BasicBlock, Vec<BasicBlock>>>,
+    cache: cache::Cache,
 }
 
 impl<'tcx> Body<'tcx> {
@@ -191,7 +192,7 @@ impl<'tcx> Body<'tcx> {
             spread_arg: None,
             var_debug_info,
             span,
-            predecessors_cache: None,
+            cache: cache::Cache::new(),
             control_flow_destroyed,
         }
     }
@@ -204,7 +205,7 @@ impl<'tcx> Body<'tcx> {
     #[inline]
     pub fn basic_blocks_mut(&mut self) -> &mut IndexVec<BasicBlock, BasicBlockData<'tcx>> {
         debug!("bbm: Clearing predecessors cache for body at: {:?}", self.span.data());
-        self.predecessors_cache = None;
+        self.cache.invalidate_predecessors();
         &mut self.basic_blocks
     }
 
@@ -213,23 +214,23 @@ impl<'tcx> Body<'tcx> {
         &mut self,
     ) -> (&mut IndexVec<BasicBlock, BasicBlockData<'tcx>>, &mut LocalDecls<'tcx>) {
         debug!("bbaldm: Clearing predecessors cache for body at: {:?}", self.span.data());
-        self.predecessors_cache = None;
+        self.cache.invalidate_predecessors();
         (&mut self.basic_blocks, &mut self.local_decls)
     }
 
     #[inline]
     pub fn unwrap_predecessors(&self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
         assert!(
-            self.predecessors_cache.is_some(),
-            "Expected predecessors_cache to be `Some(...)` for block at: {:?}",
+            self.cache.predecessors.is_some(),
+            "Expected cache.predecessors to be `Some(...)` for block at: {:?}",
             self.span.data()
         );
-        self.predecessors_cache.as_ref().unwrap()
+        self.cache.predecessors.as_ref().unwrap()
     }
 
     #[inline]
     pub fn ensure_predecessors(&mut self) {
-        if self.predecessors_cache.is_none() {
+        if self.cache.predecessors.is_none() {
             let mut result = IndexVec::from_elem(vec![], self.basic_blocks());
             for (bb, data) in self.basic_blocks().iter_enumerated() {
                 if let Some(ref term) = data.terminator {
@@ -239,7 +240,7 @@ impl<'tcx> Body<'tcx> {
                 }
             }
 
-            self.predecessors_cache = Some(result)
+            self.cache.predecessors = Some(result)
         }
     }
 
@@ -247,7 +248,7 @@ impl<'tcx> Body<'tcx> {
     /// This will recompute the predecessors cache if it is not available
     pub fn predecessors(&mut self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
         self.ensure_predecessors();
-        self.predecessors_cache.as_ref().unwrap()
+        self.cache.predecessors.as_ref().unwrap()
     }
 
     #[inline]
@@ -1030,8 +1031,6 @@ impl BasicBlock {
     }
 }
 
-CloneTypeFoldableAndLiftImpls!{ BasicBlock, }
-
 ///////////////////////////////////////////////////////////////////////////
 // BasicBlockData and Terminator
 
diff --git a/src/librustc_metadata/rmeta/decoder.rs b/src/librustc_metadata/rmeta/decoder.rs
index 820783bab6d..bbf28418f11 100644
--- a/src/librustc_metadata/rmeta/decoder.rs
+++ b/src/librustc_metadata/rmeta/decoder.rs
@@ -1082,7 +1082,7 @@ impl<'a, 'tcx> CrateMetadata {
 
     fn get_optimized_mir(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> Body<'tcx> {
         self.root.per_def.mir.get(self, id)
-            .filter(|_| !self.is_proc_macro(id))
+        self.entry_unless_proc_macro(id)
             .unwrap_or_else(|| {
                 bug!("get_optimized_mir: missing MIR for `{:?}`", self.local_def_id(id))
             })
diff --git a/src/librustc_mir/transform/mod.rs b/src/librustc_mir/transform/mod.rs
index 156ef4c3b8a..e80fb936170 100644
--- a/src/librustc_mir/transform/mod.rs
+++ b/src/librustc_mir/transform/mod.rs
@@ -249,8 +249,9 @@ fn mir_validated(
         // What we need to run borrowck etc.
         &promote_pass,
         &simplify::SimplifyCfg::new("qualify-consts"),
-        &ensure_predecessors_cache::EnsurePredecessorsCache::new("qualify-consts"),
     ]);
+
+    body.ensure_predecessors();
     let promoted = promote_pass.promoted_fragments.into_inner();
     (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
 }