diff --git a/.gitignore b/.gitignore
index 0d20b6487c..002a368e2b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,5 @@
 *.pyc
+*.bk
+*.swp
+*.swo
+tags
diff --git a/src/libcretonne/cfg.rs b/src/libcretonne/cfg.rs
new file mode 100644
index 0000000000..4fc2f1b292
--- /dev/null
+++ b/src/libcretonne/cfg.rs
@@ -0,0 +1,185 @@
+//! A control flow graph represented as mappings of extended basic blocks to their predecessors.
+//! Predecessors are denoted by tuples of EBB and branch/jump instructions. Each predecessor
+//! tuple corresponds to the end of a basic block.
+//!
+//! ```c
+//!     Ebb0:
+//!         ...          ; beginning of basic block
+//!
+//!         ...
+//!
+//!         brz vx, Ebb1 ; end of basic block
+//!
+//!         ...          ; beginning of basic block
+//!
+//!         ...
+//!
+//!         jmp Ebb2     ; end of basic block
+//! ```
+//!
+//! Here Ebb1 and Ebb2 would each have a single predecessor denoted as (Ebb0, `brz vx, Ebb1`)
+//! and (Ebb0, `jmp Ebb2`) respectively.
+
+use repr::Function;
+use entities::{Inst, Ebb};
+use instructions::InstructionData;
+use std::collections::{BTreeSet, BTreeMap, btree_map};
+
+/// A basic block denoted by its enclosing Ebb and last instruction.
+pub type Predecessor = (Ebb, Inst);
+
+/// Storing predecessors in a BTreeSet ensures that their ordering is
+/// stable with no duplicates.
+pub type PredecessorSet = BTreeSet<Predecessor>;
+
+/// The Control Flow Graph maintains a mapping of ebbs to their predecessors
+/// where predecessors are basic blocks.
+#[derive(Debug)]
+pub struct ControlFlowGraph {
+    data: BTreeMap<Ebb, PredecessorSet>,
+}
+
+impl ControlFlowGraph {
+    /// During initialization mappings will be generated for any existing
+    /// blocks within the CFG's associated function. Basic sanity checks will
+    /// also be performed to ensure that the blocks are well formed.
+    pub fn new(func: &Function) -> ControlFlowGraph {
+        let mut cfg = ControlFlowGraph { data: BTreeMap::new() };
+
+        // Even ebbs without predecessors should show up in the CFG, albeit
+        // with no entires.
+        for ebb in func.ebbs_numerically() {
+            cfg.init_ebb(ebb);
+        }
+
+        for ebb in func.ebbs_numerically() {
+            // Flips to true when a terminating instruction is seen. So that if additional
+            // instructions occur an error may be returned.
+            for inst in func.ebb_insts(ebb) {
+                match func[inst] {
+                    InstructionData::Branch { ty: _, opcode: _, ref data } => {
+                        cfg.add_predecessor(data.destination, (ebb, inst));
+                    }
+                    InstructionData::Jump { ty: _, opcode: _, ref data } => {
+                        cfg.add_predecessor(data.destination, (ebb, inst));
+                    }
+                    _ => (),
+                }
+            }
+        }
+        cfg
+    }
+
+    /// Initializes a predecessor set for some ebb. If an ebb already has an
+    /// entry it will be clobbered.
+    pub fn init_ebb(&mut self, ebb: Ebb) -> &mut PredecessorSet {
+        self.data.insert(ebb, BTreeSet::new());
+        self.data.get_mut(&ebb).unwrap()
+    }
+
+    pub fn add_predecessor(&mut self, ebb: Ebb, predecessor: Predecessor) {
+        self.data.get_mut(&ebb).unwrap().insert(predecessor);
+    }
+
+    /// Returns all of the predecessors for some ebb, if it has an entry.
+    pub fn get_predecessors(&self, ebb: Ebb) -> Option<&PredecessorSet> {
+        self.data.get(&ebb)
+    }
+
+    /// An iterator over all of the ebb to predecessor mappings in the CFG.
+    pub fn iter<'a>(&'a self) -> btree_map::Iter<'a, Ebb, PredecessorSet> {
+        self.data.iter()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use instructions::*;
+    use entities::{Ebb, Inst, NO_VALUE};
+    use repr::Function;
+    use super::*;
+    use types;
+
+    // Some instructions will be re-used in several tests.
+
+    fn jump(func: &mut Function, dest: Ebb) -> Inst {
+        func.make_inst(InstructionData::Jump {
+            opcode: Opcode::Jump,
+            ty: types::VOID,
+            data: Box::new(JumpData {
+                destination: dest,
+                arguments: VariableArgs::new(),
+            }),
+        })
+    }
+
+    fn branch(func: &mut Function, dest: Ebb) -> Inst {
+        func.make_inst(InstructionData::Branch {
+            opcode: Opcode::Brz,
+            ty: types::VOID,
+            data: Box::new(BranchData {
+                arg: NO_VALUE,
+                destination: dest,
+                arguments: VariableArgs::new(),
+            }),
+        })
+    }
+
+    #[test]
+    fn empty() {
+        let func = Function::new();
+        let cfg = ControlFlowGraph::new(&func);
+        assert_eq!(None, cfg.iter().next());
+    }
+
+    #[test]
+    fn no_predecessors() {
+        let mut func = Function::new();
+        func.make_ebb();
+        func.make_ebb();
+        func.make_ebb();
+        let cfg = ControlFlowGraph::new(&func);
+        let nodes = cfg.iter().collect::<Vec<_>>();
+        assert_eq!(nodes.len(), 3);
+
+        let mut fun_ebbs = func.ebbs_numerically();
+        for (ebb, predecessors) in nodes {
+            assert_eq!(ebb.index(), fun_ebbs.next().unwrap().index());
+            assert_eq!(predecessors.len(), 0);
+        }
+    }
+
+    #[test]
+    fn branches_and_jumps() {
+        let mut func = Function::new();
+        let ebb0 = func.make_ebb();
+        let ebb1 = func.make_ebb();
+        let ebb2 = func.make_ebb();
+
+        let br_ebb0_ebb2 = branch(&mut func, ebb2);
+        func.append_inst(ebb0, br_ebb0_ebb2);
+
+        let jmp_ebb0_ebb1 = jump(&mut func, ebb1);
+        func.append_inst(ebb0, jmp_ebb0_ebb1);
+
+        let br_ebb1_ebb1 = branch(&mut func, ebb1);
+        func.append_inst(ebb1, br_ebb1_ebb1);
+
+        let jmp_ebb1_ebb2 = jump(&mut func, ebb2);
+        func.append_inst(ebb1, jmp_ebb1_ebb2);
+
+        let cfg = ControlFlowGraph::new(&func);
+        let ebb0_predecessors = cfg.get_predecessors(ebb0).unwrap();
+        let ebb1_predecessors = cfg.get_predecessors(ebb1).unwrap();
+        let ebb2_predecessors = cfg.get_predecessors(ebb2).unwrap();
+        assert_eq!(ebb0_predecessors.len(), 0);
+        assert_eq!(ebb1_predecessors.len(), 2);
+        assert_eq!(ebb2_predecessors.len(), 2);
+
+        assert_eq!(ebb1_predecessors.contains(&(ebb0, jmp_ebb0_ebb1)), true);
+        assert_eq!(ebb1_predecessors.contains(&(ebb1, br_ebb1_ebb1)), true);
+        assert_eq!(ebb2_predecessors.contains(&(ebb0, br_ebb0_ebb2)), true);
+        assert_eq!(ebb2_predecessors.contains(&(ebb1, jmp_ebb1_ebb2)), true);
+    }
+
+}
diff --git a/src/libcretonne/entities.rs b/src/libcretonne/entities.rs
index 6294a8e8c7..c87ed6a818 100644
--- a/src/libcretonne/entities.rs
+++ b/src/libcretonne/entities.rs
@@ -24,7 +24,7 @@ use std::fmt::{self, Display, Formatter};
 use std::u32;
 
 /// An opaque reference to an extended basic block in a function.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub struct Ebb(u32);
 
 impl Ebb {
@@ -64,7 +64,7 @@ impl Default for Ebb {
 }
 
 /// An opaque reference to an instruction in a function.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub struct Inst(u32);
 
 impl Inst {
diff --git a/src/libcretonne/lib.rs b/src/libcretonne/lib.rs
index 26fc74f7ab..f0bf55af39 100644
--- a/src/libcretonne/lib.rs
+++ b/src/libcretonne/lib.rs
@@ -14,3 +14,4 @@ pub mod entities;
 pub mod instructions;
 pub mod repr;
 pub mod write;
+pub mod cfg;