diff --git a/cranelift/src/filetest/binemit.rs b/cranelift/src/filetest/binemit.rs
index 09a6955b5e..af6e72f21e 100644
--- a/cranelift/src/filetest/binemit.rs
+++ b/cranelift/src/filetest/binemit.rs
@@ -107,11 +107,11 @@ impl SubTest for TestBinEmit {
         // Give an encoding to any instruction that doesn't already have one.
         for ebb in func.layout.ebbs() {
             for inst in func.layout.ebb_insts(ebb) {
-                if !func.encodings.get_or_default(inst).is_legal() {
+                if !func.encodings[inst].is_legal() {
                     if let Ok(enc) = isa.encode(&func.dfg,
                                                 &func.dfg[inst],
                                                 func.dfg.ctrl_typevar(inst)) {
-                        *func.encodings.ensure(inst) = enc;
+                        func.encodings[inst] = enc;
                     }
                 }
             }
@@ -158,7 +158,7 @@ impl SubTest for TestBinEmit {
                        ebb);
             for inst in func.layout.ebb_insts(ebb) {
                 sink.text.clear();
-                let enc = func.encodings.get_or_default(inst);
+                let enc = func.encodings[inst];
 
                 // Send legal encodings into the emitter.
                 if enc.is_legal() {
diff --git a/lib/cretonne/src/binemit/relaxation.rs b/lib/cretonne/src/binemit/relaxation.rs
index e49b534624..51d288703c 100644
--- a/lib/cretonne/src/binemit/relaxation.rs
+++ b/lib/cretonne/src/binemit/relaxation.rs
@@ -67,7 +67,7 @@ pub fn relax_branches(func: &mut Function, isa: &TargetIsa) -> Result<CodeOffset
             }
 
             while let Some(inst) = cur.next_inst() {
-                let enc = cur.func.encodings.get_or_default(inst);
+                let enc = cur.func.encodings[inst];
                 let size = encinfo.bytes(enc);
 
                 // See if this might be a branch that is out of range.
diff --git a/lib/cretonne/src/cursor.rs b/lib/cretonne/src/cursor.rs
index 3719aa1d34..66e87ccb9f 100644
--- a/lib/cretonne/src/cursor.rs
+++ b/lib/cretonne/src/cursor.rs
@@ -157,7 +157,7 @@ impl<'c, 'f> ir::InstInserterBase<'c> for &'c mut EncCursor<'f> {
         // Assign an encoding.
         match self.isa
                   .encode(&self.func.dfg, &self.func.dfg[inst], ctrl_typevar) {
-            Ok(e) => *self.func.encodings.ensure(inst) = e,
+            Ok(e) => self.func.encodings[inst] = e,
             Err(_) => panic!("can't encode {}", self.display_inst(inst)),
         }
 
diff --git a/lib/cretonne/src/dominator_tree.rs b/lib/cretonne/src/dominator_tree.rs
index d88adbd4a0..bb80bd3687 100644
--- a/lib/cretonne/src/dominator_tree.rs
+++ b/lib/cretonne/src/dominator_tree.rs
@@ -1,6 +1,6 @@
 //! A Dominator Tree represented as mappings of Ebbs to their immediate dominator.
 
-use entity_map::EntityMap;
+use entity::EntityMap;
 use flowgraph::{ControlFlowGraph, BasicBlock};
 use ir::{Ebb, Inst, Function, Layout, ProgramOrder, ExpandedProgramPoint};
 use packed_option::PackedOption;
@@ -339,7 +339,7 @@ impl DominatorTree {
     pub fn recompute_split_ebb(&mut self, old_ebb: Ebb, new_ebb: Ebb, split_jump_inst: Inst) {
         if !self.is_reachable(old_ebb) {
             // old_ebb is unreachable, it stays so and new_ebb is unreachable too
-            *self.nodes.ensure(new_ebb) = Default::default();
+            self.nodes[new_ebb] = Default::default();
             return;
         }
         // We use the RPO comparison on the postorder list so we invert the operands of the
@@ -350,7 +350,7 @@ impl DominatorTree {
                 .binary_search_by(|probe| self.rpo_cmp_ebb(old_ebb, *probe))
                 .expect("the old ebb is not declared to the dominator tree");
         let new_ebb_rpo = self.insert_after_rpo(old_ebb, old_ebb_postorder_index, new_ebb);
-        *self.nodes.ensure(new_ebb) = DomNode {
+        self.nodes[new_ebb] = DomNode {
             rpo_number: new_ebb_rpo,
             idom: Some(split_jump_inst).into(),
         };
diff --git a/lib/cretonne/src/entity/keys.rs b/lib/cretonne/src/entity/keys.rs
new file mode 100644
index 0000000000..795e896a00
--- /dev/null
+++ b/lib/cretonne/src/entity/keys.rs
@@ -0,0 +1,55 @@
+//! A double-ended iterator over entity references.
+
+use entity::EntityRef;
+use std::marker::PhantomData;
+
+/// Iterate over all keys in order.
+pub struct Keys<K: EntityRef> {
+    pos: usize,
+    rev_pos: usize,
+    unused: PhantomData<K>,
+}
+
+impl<K: EntityRef> Keys<K> {
+    /// Create a `Keys` iterator that visits `count` entities starting from 0.
+    pub fn new(count: usize) -> Keys<K> {
+        Keys {
+            pos: 0,
+            rev_pos: count,
+            unused: PhantomData,
+        }
+    }
+}
+
+impl<K: EntityRef> Iterator for Keys<K> {
+    type Item = K;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.pos < self.rev_pos {
+            let k = K::new(self.pos);
+            self.pos += 1;
+            Some(k)
+        } else {
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let size = self.rev_pos - self.pos;
+        (size, Some(size))
+    }
+}
+
+impl<K: EntityRef> DoubleEndedIterator for Keys<K> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.rev_pos > self.pos {
+            let k = K::new(self.rev_pos - 1);
+            self.rev_pos -= 1;
+            Some(k)
+        } else {
+            None
+        }
+    }
+}
+
+impl<K: EntityRef> ExactSizeIterator for Keys<K> {}
diff --git a/lib/cretonne/src/entity/map.rs b/lib/cretonne/src/entity/map.rs
new file mode 100644
index 0000000000..ca6f1ff7d9
--- /dev/null
+++ b/lib/cretonne/src/entity/map.rs
@@ -0,0 +1,135 @@
+//! Densely numbered entity references as mapping keys.
+//!
+//! The `EntityMap` data structure uses the dense index space to implement a map with a vector.
+//! Unlike `PrimaryMap`, and `EntityMap` can't be used to allocate entity references. It is used to
+//! associate secondary information with entities.
+
+use entity::{EntityRef, Keys};
+use std::marker::PhantomData;
+use std::ops::{Index, IndexMut};
+
+/// A mapping `K -> V` for densely indexed entity references.
+#[derive(Debug, Clone)]
+pub struct EntityMap<K, V>
+    where K: EntityRef,
+          V: Clone
+{
+    elems: Vec<V>,
+    default: V,
+    unused: PhantomData<K>,
+}
+
+/// Shared `EntityMap` implementation for all value types.
+impl<K, V> EntityMap<K, V>
+    where K: EntityRef,
+          V: Clone
+{
+    /// Create a new empty map.
+    pub fn new() -> Self
+        where V: Default
+    {
+        EntityMap {
+            elems: Vec::new(),
+            default: Default::default(),
+            unused: PhantomData,
+        }
+    }
+
+    /// Get the element at `k` if it exists.
+    pub fn get(&self, k: K) -> Option<&V> {
+        self.elems.get(k.index())
+    }
+
+    /// Is this map completely empty?
+    pub fn is_empty(&self) -> bool {
+        self.elems.is_empty()
+    }
+
+    /// Remove all entries from this map.
+    pub fn clear(&mut self) {
+        self.elems.clear()
+    }
+
+    /// Iterate over all the keys in this map.
+    pub fn keys(&self) -> Keys<K> {
+        Keys::new(self.elems.len())
+    }
+
+    /// Resize the map to have `n` entries by adding default entries as needed.
+    pub fn resize(&mut self, n: usize) {
+        self.elems.resize(n, self.default.clone());
+    }
+}
+
+/// Immutable indexing into an `EntityMap`.
+///
+/// All keys are permitted. Untouched entries have the default value.
+impl<K, V> Index<K> for EntityMap<K, V>
+    where K: EntityRef,
+          V: Clone
+{
+    type Output = V;
+
+    fn index(&self, k: K) -> &V {
+        self.get(k).unwrap_or(&self.default)
+    }
+}
+
+/// Mutable indexing into an `EntityMap`.
+///
+/// The map grows as needed to accommodate new keys.
+impl<K, V> IndexMut<K> for EntityMap<K, V>
+    where K: EntityRef,
+          V: Clone
+{
+    fn index_mut(&mut self, k: K) -> &mut V {
+        let i = k.index();
+        if i >= self.elems.len() {
+            self.resize(i + 1);
+        }
+        &mut self.elems[i]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // `EntityRef` impl for testing.
+    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+    struct E(u32);
+
+    impl EntityRef for E {
+        fn new(i: usize) -> Self {
+            E(i as u32)
+        }
+        fn index(self) -> usize {
+            self.0 as usize
+        }
+    }
+
+    #[test]
+    fn basic() {
+        let r0 = E(0);
+        let r1 = E(1);
+        let r2 = E(2);
+        let mut m = EntityMap::new();
+
+        let v: Vec<E> = m.keys().collect();
+        assert_eq!(v, []);
+
+        m[r2] = 3;
+        m[r1] = 5;
+
+        assert_eq!(m[r1], 5);
+        assert_eq!(m[r2], 3);
+
+        let v: Vec<E> = m.keys().collect();
+        assert_eq!(v, [r0, r1, r2]);
+
+        let shared = &m;
+        assert_eq!(shared[r0], 0);
+        assert_eq!(shared[r1], 5);
+        assert_eq!(shared[r2], 3);
+    }
+}
diff --git a/lib/cretonne/src/entity/mod.rs b/lib/cretonne/src/entity/mod.rs
index 26c1e54353..58f900abc4 100644
--- a/lib/cretonne/src/entity/mod.rs
+++ b/lib/cretonne/src/entity/mod.rs
@@ -5,6 +5,14 @@
 //!
 //! Various data structures based on the entity references are defined in sub-modules.
 
+mod keys;
+mod map;
+mod primary;
+
+pub use self::keys::Keys;
+pub use self::map::EntityMap;
+pub use self::primary::PrimaryMap;
+
 /// A type wrapping a small integer index should implement `EntityRef` so it can be used as the key
 /// of an `EntityMap` or `SparseMap`.
 pub trait EntityRef: Copy + Eq {
diff --git a/lib/cretonne/src/entity/primary.rs b/lib/cretonne/src/entity/primary.rs
new file mode 100644
index 0000000000..e98698f117
--- /dev/null
+++ b/lib/cretonne/src/entity/primary.rs
@@ -0,0 +1,141 @@
+//! Densely numbered entity references as mapping keys.
+//!
+//! The `PrimaryMap` data structure uses the dense index space to implement a map with a vector.
+//!
+//! A primary map contains the main definition of an entity, and it can be used to allocate new
+//! entity references with the `push` method.
+//!
+//! There should only be a single `PrimaryMap` instance for a given `EntityRef` type, otherwise
+//! conflicting references will be created.
+
+use entity::{EntityRef, Keys};
+use std::marker::PhantomData;
+use std::ops::{Index, IndexMut};
+
+/// A mapping `K -> V` for densely indexed entity references.
+#[derive(Debug, Clone)]
+pub struct PrimaryMap<K, V>
+    where K: EntityRef
+{
+    elems: Vec<V>,
+    unused: PhantomData<K>,
+}
+
+impl<K, V> PrimaryMap<K, V>
+    where K: EntityRef
+{
+    /// Create a new empty map.
+    pub fn new() -> Self {
+        PrimaryMap {
+            elems: Vec::new(),
+            unused: PhantomData,
+        }
+    }
+
+    /// Check if `k` is a valid key in the map.
+    pub fn is_valid(&self, k: K) -> bool {
+        k.index() < self.elems.len()
+    }
+
+    /// Get the element at `k` if it exists.
+    pub fn get(&self, k: K) -> Option<&V> {
+        self.elems.get(k.index())
+    }
+
+    /// Is this map completely empty?
+    pub fn is_empty(&self) -> bool {
+        self.elems.is_empty()
+    }
+
+    /// Get the total number of entity references created.
+    pub fn len(&self) -> usize {
+        self.elems.len()
+    }
+
+    /// Iterate over all the keys in this map.
+    pub fn keys(&self) -> Keys<K> {
+        Keys::new(self.elems.len())
+    }
+
+    /// Remove all entries from this map.
+    pub fn clear(&mut self) {
+        self.elems.clear()
+    }
+
+    /// Get the key that will be assigned to the next pushed value.
+    pub fn next_key(&self) -> K {
+        K::new(self.elems.len())
+    }
+
+    /// Append `v` to the mapping, assigning a new key which is returned.
+    pub fn push(&mut self, v: V) -> K {
+        let k = self.next_key();
+        self.elems.push(v);
+        k
+    }
+}
+
+/// Immutable indexing into an `PrimaryMap`.
+/// The indexed value must be in the map.
+impl<K, V> Index<K> for PrimaryMap<K, V>
+    where K: EntityRef
+{
+    type Output = V;
+
+    fn index(&self, k: K) -> &V {
+        &self.elems[k.index()]
+    }
+}
+
+/// Mutable indexing into an `PrimaryMap`.
+impl<K, V> IndexMut<K> for PrimaryMap<K, V>
+    where K: EntityRef
+{
+    fn index_mut(&mut self, k: K) -> &mut V {
+        &mut self.elems[k.index()]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // `EntityRef` impl for testing.
+    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+    struct E(u32);
+
+    impl EntityRef for E {
+        fn new(i: usize) -> Self {
+            E(i as u32)
+        }
+        fn index(self) -> usize {
+            self.0 as usize
+        }
+    }
+
+    #[test]
+    fn basic() {
+        let r0 = E(0);
+        let r1 = E(1);
+        let m = PrimaryMap::<E, isize>::new();
+
+        let v: Vec<E> = m.keys().collect();
+        assert_eq!(v, []);
+
+        assert!(!m.is_valid(r0));
+        assert!(!m.is_valid(r1));
+    }
+
+    #[test]
+    fn push() {
+        let mut m = PrimaryMap::new();
+        let k1: E = m.push(12);
+        let k2 = m.push(33);
+
+        assert_eq!(m[k1], 12);
+        assert_eq!(m[k2], 33);
+
+        let v: Vec<E> = m.keys().collect();
+        assert_eq!(v, [k1, k2]);
+    }
+}
diff --git a/lib/cretonne/src/entity_map.rs b/lib/cretonne/src/entity_map.rs
deleted file mode 100644
index 7afb863ed0..0000000000
--- a/lib/cretonne/src/entity_map.rs
+++ /dev/null
@@ -1,263 +0,0 @@
-//! Densely numbered entity references as mapping keys.
-//!
-//! The `EntityMap` data structure uses the dense index space to implement a map with a vector.
-//! There are primary and secondary entity maps:
-//!
-//! - A *primary* `EntityMap` contains the main definition of an entity, and it can be used to
-//!   allocate new entity references with the `push` method. The values stores in a primary map
-//!   must implement the `PrimaryEntityData` marker trait.
-//! - A *secondary* `EntityMap` contains additional data about entities kept in a primary map. The
-//!   values need to implement `Clone + Default` traits so the map can be grown with `ensure`.
-
-use entity::EntityRef;
-use std::marker::PhantomData;
-use std::ops::{Index, IndexMut};
-
-/// A mapping `K -> V` for densely indexed entity references.
-#[derive(Debug, Clone)]
-pub struct EntityMap<K, V>
-    where K: EntityRef
-{
-    elems: Vec<V>,
-    unused: PhantomData<K>,
-}
-
-/// Shared `EntityMap` implementation for all value types.
-impl<K, V> EntityMap<K, V>
-    where K: EntityRef
-{
-    /// Create a new empty map.
-    pub fn new() -> Self {
-        EntityMap {
-            elems: Vec::new(),
-            unused: PhantomData,
-        }
-    }
-
-    /// Check if `k` is a valid key in the map.
-    pub fn is_valid(&self, k: K) -> bool {
-        k.index() < self.elems.len()
-    }
-
-    /// Get the element at `k` if it exists.
-    pub fn get(&self, k: K) -> Option<&V> {
-        self.elems.get(k.index())
-    }
-
-    /// Is this map completely empty?
-    pub fn is_empty(&self) -> bool {
-        self.elems.is_empty()
-    }
-
-    /// Remove all entries from this map.
-    pub fn clear(&mut self) {
-        self.elems.clear()
-    }
-
-    /// Iterate over all the keys in this map.
-    pub fn keys(&self) -> Keys<K> {
-        Keys {
-            pos: 0,
-            rev_pos: self.elems.len(),
-            unused: PhantomData,
-        }
-    }
-}
-
-/// A marker trait for data stored in primary entity maps.
-///
-/// A primary entity map can be used to allocate new entity references with the `push` method. It
-/// is important that entity references can't be created anywhere else, so the data stored in a
-/// primary entity map must be tagged as `PrimaryEntityData` to unlock the `push` method.
-pub trait PrimaryEntityData {}
-
-/// Additional methods for primary entry maps only.
-///
-/// These are identified by the `PrimaryEntityData` marker trait.
-impl<K, V> EntityMap<K, V>
-    where K: EntityRef,
-          V: PrimaryEntityData
-{
-    /// Get the key that will be assigned to the next pushed value.
-    pub fn next_key(&self) -> K {
-        K::new(self.elems.len())
-    }
-
-    /// Append `v` to the mapping, assigning a new key which is returned.
-    pub fn push(&mut self, v: V) -> K {
-        let k = self.next_key();
-        self.elems.push(v);
-        k
-    }
-
-    /// Get the total number of entity references created.
-    pub fn len(&self) -> usize {
-        self.elems.len()
-    }
-}
-
-/// Additional methods for value types that implement `Clone` and `Default`.
-///
-/// When the value type implements these additional traits, the `EntityMap` can be resized
-/// explicitly with the `ensure` method.
-///
-/// Use this for secondary maps that are mapping keys created by another primary map.
-impl<K, V> EntityMap<K, V>
-    where K: EntityRef,
-          V: Clone + Default
-{
-    /// Create a new secondary `EntityMap` that is prepared to hold `n` elements.
-    ///
-    /// Use this when the length of the primary map is known:
-    /// ```
-    /// let secondary_map = EntityMap::with_capacity(primary_map.len());
-    /// ```
-    pub fn with_capacity(n: usize) -> Self {
-        let mut map = EntityMap {
-            elems: Vec::with_capacity(n),
-            unused: PhantomData,
-        };
-        map.elems.resize(n, V::default());
-        map
-    }
-
-    /// Resize the map to have `n` entries by adding default entries as needed.
-    pub fn resize(&mut self, n: usize) {
-        self.elems.resize(n, V::default());
-    }
-
-    /// Ensure that `k` is a valid key but adding default entries if necessary.
-    ///
-    /// Return a mutable reference to the corresponding entry.
-    pub fn ensure(&mut self, k: K) -> &mut V {
-        if !self.is_valid(k) {
-            self.resize(k.index() + 1)
-        }
-        &mut self.elems[k.index()]
-    }
-
-    /// Get the element at `k` or the default value if `k` is out of range.
-    pub fn get_or_default(&self, k: K) -> V {
-        self.elems.get(k.index()).cloned().unwrap_or_default()
-    }
-}
-
-/// Immutable indexing into an `EntityMap`.
-/// The indexed value must be in the map, either because it was created by `push`, or the key was
-/// passed to `ensure`.
-impl<K, V> Index<K> for EntityMap<K, V>
-    where K: EntityRef
-{
-    type Output = V;
-
-    fn index(&self, k: K) -> &V {
-        &self.elems[k.index()]
-    }
-}
-
-/// Mutable indexing into an `EntityMap`.
-/// Use `ensure` instead if the key is not known to be valid.
-impl<K, V> IndexMut<K> for EntityMap<K, V>
-    where K: EntityRef
-{
-    fn index_mut(&mut self, k: K) -> &mut V {
-        &mut self.elems[k.index()]
-    }
-}
-
-/// Iterate over all keys in order.
-pub struct Keys<K>
-    where K: EntityRef
-{
-    pos: usize,
-    rev_pos: usize,
-    unused: PhantomData<K>,
-}
-
-impl<K> Iterator for Keys<K>
-    where K: EntityRef
-{
-    type Item = K;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.pos < self.rev_pos {
-            let k = K::new(self.pos);
-            self.pos += 1;
-            Some(k)
-        } else {
-            None
-        }
-    }
-}
-
-impl<K> DoubleEndedIterator for Keys<K>
-    where K: EntityRef
-{
-    fn next_back(&mut self) -> Option<Self::Item> {
-        if self.rev_pos > self.pos {
-            let k = K::new(self.rev_pos - 1);
-            self.rev_pos -= 1;
-            Some(k)
-        } else {
-            None
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    // `EntityRef` impl for testing.
-    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
-    struct E(u32);
-
-    impl EntityRef for E {
-        fn new(i: usize) -> Self {
-            E(i as u32)
-        }
-        fn index(self) -> usize {
-            self.0 as usize
-        }
-    }
-
-    impl PrimaryEntityData for isize {}
-
-    #[test]
-    fn basic() {
-        let r0 = E(0);
-        let r1 = E(1);
-        let r2 = E(2);
-        let mut m = EntityMap::new();
-
-        let v: Vec<E> = m.keys().collect();
-        assert_eq!(v, []);
-
-        assert!(!m.is_valid(r0));
-        m.ensure(r2);
-        m[r2] = 3;
-        assert!(m.is_valid(r1));
-        m[r1] = 5;
-
-        assert_eq!(m[r1], 5);
-        assert_eq!(m[r2], 3);
-
-        let v: Vec<E> = m.keys().collect();
-        assert_eq!(v, [r0, r1, r2]);
-
-        let shared = &m;
-        assert_eq!(shared[r0], 0);
-        assert_eq!(shared[r1], 5);
-        assert_eq!(shared[r2], 3);
-    }
-
-    #[test]
-    fn push() {
-        let mut m = EntityMap::new();
-        let k1: E = m.push(12);
-        let k2 = m.push(33);
-
-        assert_eq!(m[k1], 12);
-        assert_eq!(m[k2], 33);
-    }
-}
diff --git a/lib/cretonne/src/flowgraph.rs b/lib/cretonne/src/flowgraph.rs
index f7cb0c9729..504d90fb9d 100644
--- a/lib/cretonne/src/flowgraph.rs
+++ b/lib/cretonne/src/flowgraph.rs
@@ -25,7 +25,7 @@
 
 use ir::{Function, Inst, Ebb};
 use ir::instructions::BranchInfo;
-use entity_map::EntityMap;
+use entity::EntityMap;
 use std::mem;
 
 /// A basic block denoted by its enclosing Ebb and last instruction.
diff --git a/lib/cretonne/src/ir/dfg.rs b/lib/cretonne/src/ir/dfg.rs
index 959b29c8e8..219557aeb8 100644
--- a/lib/cretonne/src/ir/dfg.rs
+++ b/lib/cretonne/src/ir/dfg.rs
@@ -1,6 +1,6 @@
 //! Data flow graph tracking Instructions, Values, and EBBs.
 
-use entity_map::{EntityMap, PrimaryEntityData};
+use entity::{PrimaryMap, EntityMap};
 use isa::TargetIsa;
 use ir::builder::{InsertBuilder, ReplaceBuilder};
 use ir::extfunc::ExtFuncData;
@@ -27,7 +27,7 @@ pub struct DataFlowGraph {
     /// Data about all of the instructions in the function, including opcodes and operands.
     /// The instructions in this map are not in program order. That is tracked by `Layout`, along
     /// with the EBB containing each instruction.
-    insts: EntityMap<Inst, InstructionData>,
+    insts: PrimaryMap<Inst, InstructionData>,
 
     /// List of result values for each instruction.
     ///
@@ -38,7 +38,7 @@ pub struct DataFlowGraph {
     /// Extended basic blocks in the function and their arguments.
     /// This map is not in program order. That is handled by `Layout`, and so is the sequence of
     /// instructions contained in each EBB.
-    ebbs: EntityMap<Ebb, EbbData>,
+    ebbs: PrimaryMap<Ebb, EbbData>,
 
     /// Memory pool of value lists.
     ///
@@ -50,33 +50,27 @@ pub struct DataFlowGraph {
     pub value_lists: ValueListPool,
 
     /// Primary value table with entries for all values.
-    values: EntityMap<Value, ValueData>,
+    values: PrimaryMap<Value, ValueData>,
 
     /// Function signature table. These signatures are referenced by indirect call instructions as
     /// well as the external function references.
-    pub signatures: EntityMap<SigRef, Signature>,
+    pub signatures: PrimaryMap<SigRef, Signature>,
 
     /// External function references. These are functions that can be called directly.
-    pub ext_funcs: EntityMap<FuncRef, ExtFuncData>,
+    pub ext_funcs: PrimaryMap<FuncRef, ExtFuncData>,
 }
 
-impl PrimaryEntityData for InstructionData {}
-impl PrimaryEntityData for EbbData {}
-impl PrimaryEntityData for ValueData {}
-impl PrimaryEntityData for Signature {}
-impl PrimaryEntityData for ExtFuncData {}
-
 impl DataFlowGraph {
     /// Create a new empty `DataFlowGraph`.
     pub fn new() -> DataFlowGraph {
         DataFlowGraph {
-            insts: EntityMap::new(),
+            insts: PrimaryMap::new(),
             results: EntityMap::new(),
-            ebbs: EntityMap::new(),
+            ebbs: PrimaryMap::new(),
             value_lists: ValueListPool::new(),
-            values: EntityMap::new(),
-            signatures: EntityMap::new(),
-            ext_funcs: EntityMap::new(),
+            values: PrimaryMap::new(),
+            signatures: PrimaryMap::new(),
+            ext_funcs: PrimaryMap::new(),
         }
     }
 
@@ -115,7 +109,7 @@ impl DataFlowGraph {
 /// Resolve value aliases.
 ///
 /// Find the original SSA value that `value` aliases.
-fn resolve_aliases(values: &EntityMap<Value, ValueData>, value: Value) -> Value {
+fn resolve_aliases(values: &PrimaryMap<Value, ValueData>, value: Value) -> Value {
     let mut v = value;
 
     // Note that values may be empty here.
diff --git a/lib/cretonne/src/ir/function.rs b/lib/cretonne/src/ir/function.rs
index 028c376479..c9d0031deb 100644
--- a/lib/cretonne/src/ir/function.rs
+++ b/lib/cretonne/src/ir/function.rs
@@ -3,9 +3,10 @@
 //! The `Function` struct defined in this module owns all of its extended basic blocks and
 //! instructions.
 
-use entity_map::{EntityMap, PrimaryEntityData};
-use ir::{FunctionName, CallConv, Signature, JumpTableData, GlobalVarData, DataFlowGraph, Layout};
-use ir::{JumpTables, InstEncodings, ValueLocations, StackSlots, GlobalVars, EbbOffsets};
+use entity::{PrimaryMap, EntityMap};
+use ir;
+use ir::{FunctionName, CallConv, Signature, DataFlowGraph, Layout};
+use ir::{InstEncodings, ValueLocations, JumpTables, StackSlots, EbbOffsets};
 use isa::TargetIsa;
 use std::fmt;
 use write::write_function;
@@ -26,7 +27,7 @@ pub struct Function {
     pub stack_slots: StackSlots,
 
     /// Global variables referenced.
-    pub global_vars: GlobalVars,
+    pub global_vars: PrimaryMap<ir::GlobalVar, ir::GlobalVarData>,
 
     /// Jump tables used in this function.
     pub jump_tables: JumpTables,
@@ -52,9 +53,6 @@ pub struct Function {
     pub offsets: EbbOffsets,
 }
 
-impl PrimaryEntityData for JumpTableData {}
-impl PrimaryEntityData for GlobalVarData {}
-
 impl Function {
     /// Create a function with the given name and signature.
     pub fn with_name_signature(name: FunctionName, sig: Signature) -> Function {
@@ -62,8 +60,8 @@ impl Function {
             name,
             signature: sig,
             stack_slots: StackSlots::new(),
-            global_vars: GlobalVars::new(),
-            jump_tables: EntityMap::new(),
+            global_vars: PrimaryMap::new(),
+            jump_tables: PrimaryMap::new(),
             dfg: DataFlowGraph::new(),
             layout: Layout::new(),
             encodings: EntityMap::new(),
diff --git a/lib/cretonne/src/ir/layout.rs b/lib/cretonne/src/ir/layout.rs
index 9e03daa8a9..ca54cefdb3 100644
--- a/lib/cretonne/src/ir/layout.rs
+++ b/lib/cretonne/src/ir/layout.rs
@@ -5,7 +5,7 @@
 
 use std::cmp;
 use std::iter::{Iterator, IntoIterator};
-use entity_map::EntityMap;
+use entity::EntityMap;
 use packed_option::PackedOption;
 use ir::{Ebb, Inst, Type, DataFlowGraph};
 use ir::builder::InstInserterBase;
@@ -278,7 +278,7 @@ impl Layout {
 impl Layout {
     /// Is `ebb` currently part of the layout?
     pub fn is_ebb_inserted(&self, ebb: Ebb) -> bool {
-        Some(ebb) == self.first_ebb || (self.ebbs.is_valid(ebb) && self.ebbs[ebb].prev.is_some())
+        Some(ebb) == self.first_ebb || self.ebbs[ebb].prev.is_some()
     }
 
     /// Insert `ebb` as the last EBB in the layout.
@@ -286,7 +286,7 @@ impl Layout {
         assert!(!self.is_ebb_inserted(ebb),
                 "Cannot append EBB that is already in the layout");
         {
-            let node = self.ebbs.ensure(ebb);
+            let node = &mut self.ebbs[ebb];
             assert!(node.first_inst.is_none() && node.last_inst.is_none());
             node.prev = self.last_ebb.into();
             node.next = None.into();
@@ -308,7 +308,7 @@ impl Layout {
                 "EBB Insertion point not in the layout");
         let after = self.ebbs[before].prev;
         {
-            let node = self.ebbs.ensure(ebb);
+            let node = &mut self.ebbs[ebb];
             node.next = before.into();
             node.prev = after;
         }
@@ -328,7 +328,7 @@ impl Layout {
                 "EBB Insertion point not in the layout");
         let before = self.ebbs[after].next;
         {
-            let node = self.ebbs.ensure(ebb);
+            let node = &mut self.ebbs[ebb];
             node.next = before;
             node.prev = after.into();
         }
@@ -406,11 +406,7 @@ impl<'f> IntoIterator for &'f Layout {
 impl Layout {
     /// Get the EBB containing `inst`, or `None` if `inst` is not inserted in the layout.
     pub fn inst_ebb(&self, inst: Inst) -> Option<Ebb> {
-        if self.insts.is_valid(inst) {
-            self.insts[inst].ebb.into()
-        } else {
-            None
-        }
+        self.insts[inst].ebb.into()
     }
 
     /// Get the EBB containing the program point `pp`. Panic if `pp` is not in the layout.
@@ -433,7 +429,7 @@ impl Layout {
         {
             let ebb_node = &mut self.ebbs[ebb];
             {
-                let inst_node = self.insts.ensure(inst);
+                let inst_node = &mut self.insts[inst];
                 inst_node.ebb = ebb.into();
                 inst_node.prev = ebb_node.last_inst;
                 assert!(inst_node.next.is_none());
@@ -465,7 +461,7 @@ impl Layout {
             .expect("Instruction before insertion point not in the layout");
         let after = self.insts[before].prev;
         {
-            let inst_node = self.insts.ensure(inst);
+            let inst_node = &mut self.insts[inst];
             inst_node.ebb = ebb.into();
             inst_node.next = before.into();
             inst_node.prev = after;
@@ -543,7 +539,7 @@ impl Layout {
         let next_ebb = self.ebbs[old_ebb].next;
         let last_inst = self.ebbs[old_ebb].last_inst;
         {
-            let node = self.ebbs.ensure(new_ebb);
+            let node = &mut self.ebbs[new_ebb];
             node.prev = old_ebb.into();
             node.next = next_ebb;
             node.first_inst = before.into();
diff --git a/lib/cretonne/src/ir/mod.rs b/lib/cretonne/src/ir/mod.rs
index 1e31e34010..75e68d110f 100644
--- a/lib/cretonne/src/ir/mod.rs
+++ b/lib/cretonne/src/ir/mod.rs
@@ -36,20 +36,17 @@ pub use ir::types::Type;
 pub use ir::valueloc::{ValueLoc, ArgumentLoc};
 
 use binemit;
-use entity_map::EntityMap;
+use entity::{PrimaryMap, EntityMap};
 use isa;
 
 /// Map of value locations.
 pub type ValueLocations = EntityMap<Value, ValueLoc>;
 
 /// Map of jump tables.
-pub type JumpTables = EntityMap<JumpTable, JumpTableData>;
+pub type JumpTables = PrimaryMap<JumpTable, JumpTableData>;
 
 /// Map of instruction encodings.
 pub type InstEncodings = EntityMap<Inst, isa::Encoding>;
 
 /// Code offsets for EBBs.
 pub type EbbOffsets = EntityMap<Ebb, binemit::CodeOffset>;
-
-/// Map of global variables.
-pub type GlobalVars = EntityMap<GlobalVar, GlobalVarData>;
diff --git a/lib/cretonne/src/ir/stackslot.rs b/lib/cretonne/src/ir/stackslot.rs
index 6f3de96cd2..528f6b22f2 100644
--- a/lib/cretonne/src/ir/stackslot.rs
+++ b/lib/cretonne/src/ir/stackslot.rs
@@ -3,7 +3,7 @@
 //! The `StackSlotData` struct keeps track of a single stack slot in a function.
 //!
 
-use entity_map::{EntityMap, PrimaryEntityData, Keys};
+use entity::{PrimaryMap, Keys};
 use ir::{Type, StackSlot};
 use std::fmt;
 use std::ops::Index;
@@ -124,15 +124,13 @@ impl fmt::Display for StackSlotData {
     }
 }
 
-impl PrimaryEntityData for StackSlotData {}
-
 /// Stack frame manager.
 ///
 /// Keep track of all the stack slots used by a function.
 #[derive(Clone, Debug)]
 pub struct StackSlots {
     /// All allocated stack slots.
-    slots: EntityMap<StackSlot, StackSlotData>,
+    slots: PrimaryMap<StackSlot, StackSlotData>,
 
     /// All the outgoing stack slots, ordered by offset.
     outgoing: Vec<StackSlot>,
@@ -152,7 +150,7 @@ impl StackSlots {
     /// Create an empty stack slot manager.
     pub fn new() -> StackSlots {
         StackSlots {
-            slots: EntityMap::new(),
+            slots: PrimaryMap::new(),
             outgoing: Vec::new(),
             frame_size: None,
         }
diff --git a/lib/cretonne/src/legalizer/boundary.rs b/lib/cretonne/src/legalizer/boundary.rs
index 6977c9e7bc..71c79ef46b 100644
--- a/lib/cretonne/src/legalizer/boundary.rs
+++ b/lib/cretonne/src/legalizer/boundary.rs
@@ -585,7 +585,7 @@ fn spill_entry_arguments(func: &mut Function, entry: Ebb) {
             .zip(func.dfg.ebb_args(entry)) {
         if let ArgumentLoc::Stack(offset) = abi.location {
             let ss = func.stack_slots.make_incoming_arg(abi.value_type, offset);
-            *func.locations.ensure(arg) = ValueLoc::Stack(ss);
+            func.locations[arg] = ValueLoc::Stack(ss);
         }
     }
 }
@@ -646,7 +646,7 @@ fn spill_call_arguments(dfg: &mut DataFlowGraph,
     // Insert the spill instructions and rewrite call arguments.
     for (idx, arg, ss) in arglist {
         let stack_val = dfg.ins(pos).spill(arg);
-        *locations.ensure(stack_val) = ValueLoc::Stack(ss);
+        locations[stack_val] = ValueLoc::Stack(ss);
         dfg.inst_variable_args_mut(inst)[idx] = stack_val;
     }
 
diff --git a/lib/cretonne/src/legalizer/mod.rs b/lib/cretonne/src/legalizer/mod.rs
index faed731c95..230c7adc7e 100644
--- a/lib/cretonne/src/legalizer/mod.rs
+++ b/lib/cretonne/src/legalizer/mod.rs
@@ -73,7 +73,7 @@ pub fn legalize_function(func: &mut ir::Function,
             match isa.encode(&pos.func.dfg,
                              &pos.func.dfg[inst],
                              pos.func.dfg.ctrl_typevar(inst)) {
-                Ok(encoding) => *pos.func.encodings.ensure(inst) = encoding,
+                Ok(encoding) => pos.func.encodings[inst] = encoding,
                 Err(action) => {
                     // We should transform the instruction into legal equivalents.
                     let changed = action(inst, pos.func, cfg);
diff --git a/lib/cretonne/src/lib.rs b/lib/cretonne/src/lib.rs
index 324698c53c..6cb6687138 100644
--- a/lib/cretonne/src/lib.rs
+++ b/lib/cretonne/src/lib.rs
@@ -19,7 +19,6 @@ pub mod binemit;
 pub mod bitset;
 pub mod dominator_tree;
 pub mod entity_list;
-pub mod entity_map;
 pub mod flowgraph;
 pub mod ir;
 pub mod isa;
diff --git a/lib/cretonne/src/loop_analysis.rs b/lib/cretonne/src/loop_analysis.rs
index 5a4607ba79..55ddf1f4df 100644
--- a/lib/cretonne/src/loop_analysis.rs
+++ b/lib/cretonne/src/loop_analysis.rs
@@ -2,7 +2,8 @@
 //! and parent in the loop tree.
 
 use dominator_tree::DominatorTree;
-use entity_map::{EntityMap, PrimaryEntityData, Keys};
+use entity::{PrimaryMap, Keys};
+use entity::EntityMap;
 use flowgraph::ControlFlowGraph;
 use ir::{Function, Ebb, Layout};
 use packed_option::PackedOption;
@@ -17,7 +18,7 @@ entity_impl!(Loop, "loop");
 /// Loops are referenced by the Loop object, and for each loop you can access its header EBB,
 /// its eventual parent in the loop tree and all the EBB belonging to the loop.
 pub struct LoopAnalysis {
-    loops: EntityMap<Loop, LoopData>,
+    loops: PrimaryMap<Loop, LoopData>,
     ebb_loop_map: EntityMap<Ebb, PackedOption<Loop>>,
 }
 
@@ -26,8 +27,6 @@ struct LoopData {
     parent: PackedOption<Loop>,
 }
 
-impl PrimaryEntityData for LoopData {}
-
 impl LoopData {
     /// Creates a `LoopData` object with the loop header and its eventual parent in the loop tree.
     pub fn new(header: Ebb, parent: Option<Loop>) -> LoopData {
@@ -44,7 +43,7 @@ impl LoopAnalysis {
     /// a function.
     pub fn new() -> LoopAnalysis {
         LoopAnalysis {
-            loops: EntityMap::new(),
+            loops: PrimaryMap::new(),
             ebb_loop_map: EntityMap::new(),
         }
     }
diff --git a/lib/cretonne/src/regalloc/coloring.rs b/lib/cretonne/src/regalloc/coloring.rs
index 02e4d47f81..49f26fbd37 100644
--- a/lib/cretonne/src/regalloc/coloring.rs
+++ b/lib/cretonne/src/regalloc/coloring.rs
@@ -707,7 +707,7 @@ impl<'a> Context<'a> {
             self.divert.regmove(m.value, m.from, m.to);
             let inst = dfg.ins(pos).regmove(m.value, m.from, m.to);
             match self.isa.encode(dfg, &dfg[inst], ty) {
-                Ok(encoding) => *encodings.ensure(inst) = encoding,
+                Ok(encoding) => encodings[inst] = encoding,
                 _ => panic!("Can't encode {} {}", m.rc, dfg.display_inst(inst, self.isa)),
             }
         }
diff --git a/lib/cretonne/src/regalloc/diversion.rs b/lib/cretonne/src/regalloc/diversion.rs
index bbc5c067ae..c7c9595972 100644
--- a/lib/cretonne/src/regalloc/diversion.rs
+++ b/lib/cretonne/src/regalloc/diversion.rs
@@ -7,7 +7,7 @@
 //! These register diversions are local to an EBB. No values can be diverted when entering a new
 //! EBB.
 
-use entity_map::EntityMap;
+use entity::EntityMap;
 use ir::{Value, ValueLoc};
 use isa::RegUnit;
 
diff --git a/lib/cretonne/src/regalloc/spilling.rs b/lib/cretonne/src/regalloc/spilling.rs
index 12a938c81c..35ef526993 100644
--- a/lib/cretonne/src/regalloc/spilling.rs
+++ b/lib/cretonne/src/regalloc/spilling.rs
@@ -453,7 +453,7 @@ impl<'a> Context<'a> {
             .make_spill_slot(self.cur.func.dfg.value_type(value));
         for &v in self.virtregs.congruence_class(&value) {
             self.liveness.spill(v);
-            *self.cur.func.locations.ensure(v) = ValueLoc::Stack(ss);
+            self.cur.func.locations[v] = ValueLoc::Stack(ss);
         }
     }
 
diff --git a/lib/cretonne/src/regalloc/virtregs.rs b/lib/cretonne/src/regalloc/virtregs.rs
index 17fa641fcd..722de5a1f4 100644
--- a/lib/cretonne/src/regalloc/virtregs.rs
+++ b/lib/cretonne/src/regalloc/virtregs.rs
@@ -12,7 +12,7 @@
 //! memory-to-memory copies when a spilled value is passed as an EBB argument.
 
 use entity_list::{EntityList, ListPool};
-use entity_map::{EntityMap, PrimaryEntityData, Keys};
+use entity::{PrimaryMap, EntityMap, Keys};
 use ir::Value;
 use packed_option::PackedOption;
 use ref_slice::ref_slice;
@@ -23,7 +23,6 @@ pub struct VirtReg(u32);
 entity_impl!(VirtReg, "vreg");
 
 type ValueList = EntityList<Value>;
-impl PrimaryEntityData for ValueList {}
 
 /// Collection of virtual registers.
 ///
@@ -37,7 +36,7 @@ pub struct VirtRegs {
     ///
     /// The list of values ion a virtual register is kept sorted according to the dominator tree's
     /// RPO of the value defs.
-    vregs: EntityMap<VirtReg, ValueList>,
+    vregs: PrimaryMap<VirtReg, ValueList>,
 
     /// Each value belongs to at most one virtual register.
     value_vregs: EntityMap<Value, PackedOption<VirtReg>>,
@@ -49,7 +48,7 @@ impl VirtRegs {
     pub fn new() -> VirtRegs {
         VirtRegs {
             pool: ListPool::new(),
-            vregs: EntityMap::new(),
+            vregs: PrimaryMap::new(),
             value_vregs: EntityMap::new(),
         }
     }
@@ -63,7 +62,7 @@ impl VirtRegs {
 
     /// Get the virtual register containing `value`, if any.
     pub fn get(&self, value: Value) -> Option<VirtReg> {
-        self.value_vregs.get_or_default(value).into()
+        self.value_vregs[value].into()
     }
 
     /// Get the list of values in `vreg`. The values are ordered according to `DomTree::rpo_cmp` of
@@ -133,7 +132,7 @@ impl VirtRegs {
 
         self.vregs[vreg].extend(values.iter().cloned(), &mut self.pool);
         for &v in values {
-            *self.value_vregs.ensure(v) = vreg.into();
+            self.value_vregs[v] = vreg.into();
         }
 
         vreg
diff --git a/lib/cretonne/src/sparse_map.rs b/lib/cretonne/src/sparse_map.rs
index 84c17f7b5f..4918675d27 100644
--- a/lib/cretonne/src/sparse_map.rs
+++ b/lib/cretonne/src/sparse_map.rs
@@ -35,8 +35,7 @@
 //! - `SparseMap` requires the values to implement `SparseMapValue<K>` which means that they must
 //!   contain their own key.
 
-use entity_map::EntityMap;
-use entity::EntityRef;
+use entity::{EntityRef, EntityMap};
 use std::mem;
 use std::slice;
 use std::u32;
@@ -151,7 +150,7 @@ impl<K, V> SparseMap<K, V>
         let idx = self.dense.len();
         assert!(idx <= u32::MAX as usize, "SparseMap overflow");
         self.dense.push(value);
-        *self.sparse.ensure(key) = idx as u32;
+        self.sparse[key] = idx as u32;
         None
     }
 
diff --git a/lib/cretonne/src/verifier/liveness.rs b/lib/cretonne/src/verifier/liveness.rs
index 2dff4a6e3e..8b1ab47f4c 100644
--- a/lib/cretonne/src/verifier/liveness.rs
+++ b/lib/cretonne/src/verifier/liveness.rs
@@ -63,7 +63,7 @@ impl<'a> LivenessVerifier<'a> {
     fn check_insts(&self) -> Result {
         for ebb in self.func.layout.ebbs() {
             for inst in self.func.layout.ebb_insts(ebb) {
-                let encoding = self.func.encodings.get_or_default(inst);
+                let encoding = self.func.encodings[inst];
 
                 // Check the defs.
                 for &val in self.func.dfg.inst_results(inst) {
diff --git a/lib/cretonne/src/verifier/mod.rs b/lib/cretonne/src/verifier/mod.rs
index 0995449362..15b5219334 100644
--- a/lib/cretonne/src/verifier/mod.rs
+++ b/lib/cretonne/src/verifier/mod.rs
@@ -688,7 +688,7 @@ impl<'a> Verifier<'a> {
         for (&arg, &abi) in args.iter().zip(expected_args) {
             // Value types have already been checked by `typecheck_variable_args_iterator()`.
             if let ArgumentLoc::Stack(offset) = abi.location {
-                let arg_loc = self.func.locations.get_or_default(arg);
+                let arg_loc = self.func.locations[arg];
                 if let ValueLoc::Stack(ss) = arg_loc {
                     // Argument value is assigned to a stack slot as expected.
                     self.verify_stack_slot(inst, ss)?;
@@ -811,7 +811,7 @@ impl<'a> Verifier<'a> {
             None => return Ok(()),
         };
 
-        let encoding = self.func.encodings.get_or_default(inst);
+        let encoding = self.func.encodings[inst];
         if encoding.is_legal() {
             let verify_encoding =
                 isa.encode(&self.func.dfg,
diff --git a/lib/cretonne/src/write.rs b/lib/cretonne/src/write.rs
index d0166a1063..9004546f32 100644
--- a/lib/cretonne/src/write.rs
+++ b/lib/cretonne/src/write.rs
@@ -194,7 +194,7 @@ fn write_instruction(w: &mut Write,
             if !func.locations.is_empty() {
                 let regs = isa.register_info();
                 for &r in func.dfg.inst_results(inst) {
-                    write!(s, ",{}", func.locations.get_or_default(r).display(&regs))?
+                    write!(s, ",{}", func.locations[r].display(&regs))?
                 }
             }
             write!(s, "]")?;
diff --git a/lib/frontend/src/frontend.rs b/lib/frontend/src/frontend.rs
index 935251e89e..57c0aaa9e0 100644
--- a/lib/frontend/src/frontend.rs
+++ b/lib/frontend/src/frontend.rs
@@ -6,8 +6,7 @@ use cretonne::ir::instructions::BranchInfo;
 use cretonne::ir::function::DisplayFunction;
 use cretonne::isa::TargetIsa;
 use ssa::{SSABuilder, SideEffects, Block};
-use cretonne::entity_map::{EntityMap, PrimaryEntityData};
-use cretonne::entity::EntityRef;
+use cretonne::entity::{EntityRef, EntityMap};
 use std::hash::Hash;
 
 /// Permanent structure used for translating into Cretonne IL.
@@ -38,8 +37,6 @@ struct EbbData {
     user_arg_count: usize,
 }
 
-impl PrimaryEntityData for EbbData {}
-
 struct Position {
     ebb: Ebb,
     basic_block: Block,
@@ -231,7 +228,7 @@ impl<'a, Variable> FunctionBuilder<'a, Variable>
     pub fn create_ebb(&mut self) -> Ebb {
         let ebb = self.func.dfg.make_ebb();
         self.builder.ssa.declare_ebb_header_block(ebb);
-        *self.builder.ebbs.ensure(ebb) = EbbData {
+        self.builder.ebbs[ebb] = EbbData {
             filled: false,
             pristine: true,
             user_arg_count: 0,
@@ -286,7 +283,7 @@ impl<'a, Variable> FunctionBuilder<'a, Variable>
 
     /// In order to use a variable in a `use_var`, you need to declare its type with this method.
     pub fn declare_var(&mut self, var: Variable, ty: Type) {
-        *self.builder.types.ensure(var) = ty;
+        self.builder.types[var] = ty;
     }
 
     /// Returns the Cretonne IL value corresponding to the utilization at the current program
@@ -560,7 +557,7 @@ impl<'a, Variable> FunctionBuilder<'a, Variable>
 
     fn handle_ssa_side_effects(&mut self, side_effects: SideEffects) {
         for split_ebb in side_effects.split_ebbs_created {
-            self.builder.ebbs.ensure(split_ebb).filled = true
+            self.builder.ebbs[split_ebb].filled = true
         }
         for modified_ebb in side_effects.instructions_added_to_ebbs {
             self.builder.ebbs[modified_ebb].pristine = false
diff --git a/lib/frontend/src/ssa.rs b/lib/frontend/src/ssa.rs
index bad49c6264..54485629d7 100644
--- a/lib/frontend/src/ssa.rs
+++ b/lib/frontend/src/ssa.rs
@@ -9,8 +9,7 @@ use cretonne::ir::{Ebb, Value, Inst, Type, DataFlowGraph, JumpTables, Layout, Cu
                    InstBuilder};
 use cretonne::ir::instructions::BranchInfo;
 use std::hash::Hash;
-use cretonne::entity_map::{EntityMap, PrimaryEntityData};
-use cretonne::entity::EntityRef;
+use cretonne::entity::{EntityRef, PrimaryMap, EntityMap};
 use cretonne::packed_option::PackedOption;
 use cretonne::packed_option::ReservedValue;
 use std::u32;
@@ -41,7 +40,7 @@ pub struct SSABuilder<Variable>
     variables: EntityMap<Variable, HashMap<Block, Value>>,
     // Records the position of the basic blocks and the list of values used but not defined in the
     // block.
-    blocks: EntityMap<Block, BlockData<Variable>>,
+    blocks: PrimaryMap<Block, BlockData<Variable>>,
     // Records the basic blocks at the beginning of the `Ebb`s.
     ebb_headers: EntityMap<Ebb, PackedOption<Block>>,
 }
@@ -66,7 +65,6 @@ enum BlockData<Variable> {
     // The block is implicitely sealed at creation.
     EbbBody { predecessor: Block },
 }
-impl<Variable> PrimaryEntityData for BlockData<Variable> {}
 
 impl<Variable> BlockData<Variable> {
     fn add_predecessor(&mut self, pred: Block, inst: Inst) {
@@ -135,7 +133,7 @@ impl<Variable> SSABuilder<Variable>
     pub fn new() -> SSABuilder<Variable> {
         SSABuilder {
             variables: EntityMap::new(),
-            blocks: EntityMap::new(),
+            blocks: PrimaryMap::new(),
             ebb_headers: EntityMap::new(),
         }
     }
@@ -193,7 +191,7 @@ impl<Variable> SSABuilder<Variable>
     /// The SSA value is passed as an argument because it should be created with
     /// `ir::DataFlowGraph::append_result`.
     pub fn def_var(&mut self, var: Variable, val: Value, block: Block) {
-        self.variables.ensure(var).insert(block, val);
+        self.variables[var].insert(block, val);
     }
 
     /// Declares a use of a variable in a given basic block. Returns the SSA value corresponding
@@ -296,7 +294,7 @@ impl<Variable> SSABuilder<Variable>
                                            ebb: ebb,
                                            undef_variables: Vec::new(),
                                        }));
-        *self.ebb_headers.ensure(ebb) = block.into();
+        self.ebb_headers[ebb] = block.into();
         block
     }
     /// Gets the header block corresponding to an Ebb, panics if the Ebb or the header block
diff --git a/lib/reader/src/parser.rs b/lib/reader/src/parser.rs
index 0d96861b51..9ec7547c43 100644
--- a/lib/reader/src/parser.rs
+++ b/lib/reader/src/parser.rs
@@ -1388,7 +1388,7 @@ impl<'a> Parser<'a> {
             .expect("duplicate inst references created");
 
         if let Some(encoding) = encoding {
-            *ctx.function.encodings.ensure(inst) = encoding;
+            ctx.function.encodings[inst] = encoding;
         }
 
         if results.len() != num_results {
@@ -1421,7 +1421,7 @@ impl<'a> Parser<'a> {
                     .inst_results(inst)
                     .iter()
                     .zip(result_locations) {
-                *ctx.function.locations.ensure(value) = loc;
+                ctx.function.locations[value] = loc;
             }
         }