diff --git a/cranelift/src/libcretonne/layout.rs b/cranelift/src/libcretonne/layout.rs
new file mode 100644
index 0000000000..a870e56167
--- /dev/null
+++ b/cranelift/src/libcretonne/layout.rs
@@ -0,0 +1,142 @@
+//! Function layout.
+//!
+//! The order of extended basic blocks in a function and the order of instructions in an EBB is
+//! determined by the `Layout` data structure defined in this module.
+
+use entity_map::EntityMap;
+use entities::{Ebb, NO_EBB, Inst, NO_INST};
+
+/// The `Layout` struct determines the layout of EBBs and instructions in a function. It does not
+/// contain definitions of instructions or EBBs, but depends on `Inst` and `Ebb` entity references
+/// being defined elsewhere.
+///
+/// This data structure determines:
+///
+/// - The order of EBBs in the function.
+/// - Which EBB contains a given instruction.
+/// - The order of instructions with an EBB.
+///
+/// While data dependencies are not recorded, instruction ordering does affect control
+/// dependencies, so part of the semantics of the program are determined by the layout.
+///
+pub struct Layout {
+    // Linked list nodes for the layout order of EBBs Forms a doubly linked list, terminated in
+    // both ends by NO_EBB.
+    ebbs: EntityMap<Ebb, EbbNode>,
+
+    // Linked list nodes for the layout order of instructions. Forms a double linked list per EBB,
+    // terminated in both ends by NO_INST.
+    insts: EntityMap<Inst, InstNode>,
+
+    // First EBB in the layout order, or `NO_EBB` when no EBBs have been laid out.
+    first_ebb: Ebb,
+
+    // Last EBB in the layout order, or `NO_EBB` when no EBBs have been laid out.
+    last_ebb: Ebb,
+}
+
+impl Layout {
+    /// Create a new empty `Layout`.
+    pub fn new() -> Layout {
+        Layout {
+            ebbs: EntityMap::new(),
+            insts: EntityMap::new(),
+            first_ebb: NO_EBB,
+            last_ebb: NO_EBB,
+        }
+    }
+}
+
+/// Methods for laying out EBBs.
+///
+/// An unknown EBB starts out as *not inserted* in the EBB layout. The layout is a linear order of
+/// inserted EBBs. Once an EBB has been inserted in the layout, instructions can be added. An EBB
+/// can only be removed from the layout when it is empty.
+///
+/// Since every EBB must end with a terminator instruction which cannot fall through, the layout of
+/// EBBs does not affect the semantics of the program.
+///
+impl Layout {
+    /// Is `ebb` currently part of the layout?
+    pub fn is_ebb_inserted(&self, ebb: Ebb) -> bool {
+        ebb != self.first_ebb && self.ebbs.is_valid(ebb) && self.ebbs[ebb].prev == NO_EBB
+    }
+
+    /// Insert `ebb` as the last EBB in the layout.
+    pub fn append_ebb(&mut self, ebb: Ebb) {
+        assert!(!self.is_ebb_inserted(ebb),
+                "Cannot append EBB that is already in the layout");
+        let node = &mut self.ebbs[ebb];
+        assert!(node.first_inst == NO_INST && node.last_inst == NO_INST);
+        node.prev = self.last_ebb;
+        node.next = NO_EBB;
+        self.last_ebb = ebb;
+    }
+
+    /// Insert `ebb` in the layout before the existing EBB `before`.
+    pub fn insert_ebb(&mut self, ebb: Ebb, before: Ebb) {
+        assert!(!self.is_ebb_inserted(ebb),
+                "Cannot insert EBB that is already in the layout");
+        assert!(self.is_ebb_inserted(before),
+                "EBB Insertion point not in the layout");
+        let after = self.ebbs[before].prev;
+        self.ebbs[ebb].next = before;
+        self.ebbs[ebb].prev = after;
+        self.ebbs[before].prev = ebb;
+        if after != NO_EBB {
+            self.ebbs[after].next = ebb;
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default)]
+struct EbbNode {
+    prev: Ebb,
+    next: Ebb,
+    first_inst: Inst,
+    last_inst: Inst,
+}
+
+/// Methods for arranging instructions.
+///
+/// An instruction starts out as *not inserted* in the layout. An instruction can be inserted into
+/// an EBB at a given position.
+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) {
+            let ebb = self.insts[inst].ebb;
+            if ebb == NO_EBB {
+                None
+            } else {
+                Some(ebb)
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Append `inst` to the end of `ebb`.
+    pub fn append_inst(&self, inst: Inst, ebb: Ebb) {
+        assert_eq!(self.inst_ebb(inst), None);
+        assert!(self.is_ebb_inserted(ebb),
+                "Cannot append instructions to EBB not in layout");
+        unimplemented!();
+    }
+
+    /// Insert `inst` before the instruction `before` in the same EBB.
+    pub fn insert_inst(&self, inst: Inst, before: Inst) {
+        assert_eq!(self.inst_ebb(inst), None);
+        let ebb = self.inst_ebb(before)
+            .expect("Instruction before insertion point not in the layout");
+        assert!(ebb != NO_EBB);
+        unimplemented!();
+    }
+}
+
+#[derive(Clone, Debug, Default)]
+struct InstNode {
+    ebb: Ebb,
+    prev: Inst,
+    next: Inst,
+}
diff --git a/cranelift/src/libcretonne/lib.rs b/cranelift/src/libcretonne/lib.rs
index 55d601d38b..100d3121e2 100644
--- a/cranelift/src/libcretonne/lib.rs
+++ b/cranelift/src/libcretonne/lib.rs
@@ -13,6 +13,7 @@ pub mod immediates;
 pub mod entities;
 pub mod instructions;
 pub mod repr;
+pub mod layout;
 pub mod write;
 pub mod cfg;