diff --git a/cranelift/src/libcretonne/ir/function.rs b/cranelift/src/libcretonne/ir/function.rs
new file mode 100644
index 0000000000..2f8344d801
--- /dev/null
+++ b/cranelift/src/libcretonne/ir/function.rs
@@ -0,0 +1,64 @@
+//! Intermediate representation of a function.
+//!
+//! The `Function` struct defined in this module owns all of its extended basic blocks and
+//! instructions.
+
+use ir::{FunctionName, Signature, StackSlot, StackSlotData, JumpTable, JumpTableData,
+         DataFlowGraph, Layout};
+use entity_map::{EntityMap, PrimaryEntityData};
+use std::fmt::{self, Debug, Formatter};
+
+/// A function.
+pub struct Function {
+    /// Name of this function. Mostly used by `.cton` files.
+    pub name: FunctionName,
+
+    /// Signature of this function.
+    signature: Signature,
+
+    /// Stack slots allocated in this function.
+    pub stack_slots: EntityMap<StackSlot, StackSlotData>,
+
+    /// Jump tables used in this function.
+    pub jump_tables: EntityMap<JumpTable, JumpTableData>,
+
+    /// Data flow graph containing the primary definition of all instructions, EBBs and values.
+    pub dfg: DataFlowGraph,
+
+    /// Layout of EBBs and instructions in the function body.
+    pub layout: Layout,
+}
+
+impl PrimaryEntityData for StackSlotData {}
+impl PrimaryEntityData for JumpTableData {}
+
+impl Function {
+    /// Create a function with the given name and signature.
+    pub fn with_name_signature(name: FunctionName, sig: Signature) -> Function {
+        Function {
+            name: name,
+            signature: sig,
+            stack_slots: EntityMap::new(),
+            jump_tables: EntityMap::new(),
+            dfg: DataFlowGraph::new(),
+            layout: Layout::new(),
+        }
+    }
+
+    /// Create a new empty, anomymous function.
+    pub fn new() -> Function {
+        Self::with_name_signature(FunctionName::new(), Signature::new())
+    }
+
+    /// Get the signature of this function.
+    pub fn own_signature(&self) -> &Signature {
+        &self.signature
+    }
+}
+
+impl Debug for Function {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        use write::function_to_string;
+        fmt.write_str(&function_to_string(self))
+    }
+}
diff --git a/cranelift/src/libcretonne/ir/mod.rs b/cranelift/src/libcretonne/ir/mod.rs
index 806466a90b..91f8b2516c 100644
--- a/cranelift/src/libcretonne/ir/mod.rs
+++ b/cranelift/src/libcretonne/ir/mod.rs
@@ -9,6 +9,7 @@ pub mod stackslot;
 pub mod jumptable;
 pub mod dfg;
 pub mod layout;
+pub mod function;
 
 pub use ir::types::{Type, FunctionName, Signature};
 pub use ir::entities::{Ebb, Inst, Value, StackSlot, JumpTable};
@@ -17,61 +18,4 @@ pub use ir::stackslot::StackSlotData;
 pub use ir::jumptable::JumpTableData;
 pub use ir::dfg::DataFlowGraph;
 pub use ir::layout::Layout;
-
-use std::fmt::{self, Debug, Formatter};
-use entity_map::{EntityMap, PrimaryEntityData};
-
-/// A function.
-pub struct Function {
-    /// Name of this function. Mostly used by `.cton` files.
-    pub name: FunctionName,
-
-    /// Signature of this function.
-    signature: Signature,
-
-    /// Stack slots allocated in this function.
-    pub stack_slots: EntityMap<StackSlot, StackSlotData>,
-
-    /// Jump tables used in this function.
-    pub jump_tables: EntityMap<JumpTable, JumpTableData>,
-
-    /// Data flow graph containing the primary definition of all instructions, EBBs and values.
-    pub dfg: DataFlowGraph,
-
-    /// Layout of EBBs and instructions in the function body.
-    pub layout: Layout,
-}
-
-impl PrimaryEntityData for StackSlotData {}
-impl PrimaryEntityData for JumpTableData {}
-
-impl Function {
-    /// Create a function with the given name and signature.
-    pub fn with_name_signature(name: FunctionName, sig: Signature) -> Function {
-        Function {
-            name: name,
-            signature: sig,
-            stack_slots: EntityMap::new(),
-            jump_tables: EntityMap::new(),
-            dfg: DataFlowGraph::new(),
-            layout: Layout::new(),
-        }
-    }
-
-    /// Create a new empty, anomymous function.
-    pub fn new() -> Function {
-        Self::with_name_signature(FunctionName::new(), Signature::new())
-    }
-
-    /// Get the signature of this function.
-    pub fn own_signature(&self) -> &Signature {
-        &self.signature
-    }
-}
-
-impl Debug for Function {
-    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
-        use write::function_to_string;
-        fmt.write_str(&function_to_string(self))
-    }
-}
+pub use ir::function::Function;