diff --git a/lib/codegen/src/cfg_printer.rs b/lib/codegen/src/cfg_printer.rs
index 932345ef5b..bdd57bc1cd 100644
--- a/lib/codegen/src/cfg_printer.rs
+++ b/lib/codegen/src/cfg_printer.rs
@@ -2,7 +2,7 @@
 
 use std::fmt::{Display, Formatter, Result, Write};
 
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir::instructions::BranchInfo;
 use ir::Function;
 
@@ -61,7 +61,7 @@ impl<'a> CFGPrinter<'a> {
 
     fn cfg_connections(&self, w: &mut Write) -> Result {
         for ebb in &self.func.layout {
-            for (parent, inst) in self.cfg.pred_iter(ebb) {
+            for BasicBlock { ebb: parent, inst } in self.cfg.pred_iter(ebb) {
                 writeln!(w, "    {}:{} -> {}", parent, inst, ebb)?;
             }
         }
diff --git a/lib/codegen/src/dominator_tree.rs b/lib/codegen/src/dominator_tree.rs
index ba066fe496..d8789fecb9 100644
--- a/lib/codegen/src/dominator_tree.rs
+++ b/lib/codegen/src/dominator_tree.rs
@@ -177,19 +177,19 @@ impl DominatorTree {
         layout: &Layout,
     ) -> BasicBlock {
         loop {
-            match self.rpo_cmp_ebb(a.0, b.0) {
+            match self.rpo_cmp_ebb(a.ebb, b.ebb) {
                 Ordering::Less => {
                     // `a` comes before `b` in the RPO. Move `b` up.
-                    let idom = self.nodes[b.0].idom.expect("Unreachable basic block?");
-                    b = (
+                    let idom = self.nodes[b.ebb].idom.expect("Unreachable basic block?");
+                    b = BasicBlock::new(
                         layout.inst_ebb(idom).expect("Dangling idom instruction"),
                         idom,
                     );
                 }
                 Ordering::Greater => {
                     // `b` comes before `a` in the RPO. Move `a` up.
-                    let idom = self.nodes[a.0].idom.expect("Unreachable basic block?");
-                    a = (
+                    let idom = self.nodes[a.ebb].idom.expect("Unreachable basic block?");
+                    a = BasicBlock::new(
                         layout.inst_ebb(idom).expect("Dangling idom instruction"),
                         idom,
                     );
@@ -198,10 +198,13 @@ impl DominatorTree {
             }
         }
 
-        debug_assert_eq!(a.0, b.0, "Unreachable block passed to common_dominator?");
+        debug_assert_eq!(
+            a.ebb, b.ebb,
+            "Unreachable block passed to common_dominator?"
+        );
 
         // We're in the same EBB. The common dominator is the earlier instruction.
-        if layout.cmp(a.1, b.1) == Ordering::Less {
+        if layout.cmp(a.inst, b.inst) == Ordering::Less {
             a
         } else {
             b
@@ -420,7 +423,7 @@ impl DominatorTree {
         // Note that during the first pass, `rpo_number` is 1 for reachable blocks that haven't
         // been visited yet, 0 for unreachable blocks.
         let mut reachable_preds = cfg.pred_iter(ebb)
-            .filter(|&(pred, _)| self.nodes[pred].rpo_number > 1);
+            .filter(|&BasicBlock { ebb: pred, .. }| self.nodes[pred].rpo_number > 1);
 
         // The RPO must visit at least one predecessor before this node.
         let mut idom = reachable_preds
@@ -431,7 +434,7 @@ impl DominatorTree {
             idom = self.common_dominator(idom, pred, layout);
         }
 
-        idom.1
+        idom.inst
     }
 }
 
diff --git a/lib/codegen/src/flowgraph.rs b/lib/codegen/src/flowgraph.rs
index a954b73ac1..09a9708214 100644
--- a/lib/codegen/src/flowgraph.rs
+++ b/lib/codegen/src/flowgraph.rs
@@ -31,7 +31,20 @@ use std::mem;
 use timing;
 
 /// A basic block denoted by its enclosing Ebb and last instruction.
-pub type BasicBlock = (Ebb, Inst);
+#[derive(PartialEq, Eq)]
+pub struct BasicBlock {
+    /// Enclosing Ebb key.
+    pub ebb: Ebb,
+    /// Last instruction in the basic block.
+    pub inst: Inst,
+}
+
+impl BasicBlock {
+    /// Convenient method to construct new BasicBlock.
+    pub fn new(ebb: Ebb, inst: Inst) -> Self {
+        Self { ebb, inst }
+    }
+}
 
 /// A container for the successors and predecessors of some Ebb.
 #[derive(Clone, Default)]
@@ -110,11 +123,11 @@ impl ControlFlowGraph {
         for inst in func.layout.ebb_insts(ebb) {
             match func.dfg.analyze_branch(inst) {
                 BranchInfo::SingleDest(dest, _) => {
-                    self.add_edge((ebb, inst), dest);
+                    self.add_edge(BasicBlock::new(ebb, inst), dest);
                 }
                 BranchInfo::Table(jt) => {
                     for (_, dest) in func.jump_tables[jt].entries() {
-                        self.add_edge((ebb, inst), dest);
+                        self.add_edge(BasicBlock::new(ebb, inst), dest);
                     }
                 }
                 BranchInfo::NotABranch => {}
@@ -148,12 +161,12 @@ impl ControlFlowGraph {
     }
 
     fn add_edge(&mut self, from: BasicBlock, to: Ebb) {
-        self.data[from.0]
+        self.data[from.ebb]
             .successors
             .insert(to, &mut self.succ_forest, &());
         self.data[to]
             .predecessors
-            .insert(from.1, from.0, &mut self.pred_forest, &());
+            .insert(from.inst, from.ebb, &mut self.pred_forest, &());
     }
 
     /// Get an iterator over the CFG predecessors to `ebb`.
@@ -186,7 +199,7 @@ impl<'a> Iterator for PredIter<'a> {
     type Item = BasicBlock;
 
     fn next(&mut self) -> Option<BasicBlock> {
-        self.0.next().map(|(i, e)| (e, i))
+        self.0.next().map(|(i, e)| BasicBlock::new(e, i))
     }
 }
 
@@ -268,10 +281,22 @@ mod tests {
             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);
+            assert_eq!(
+                ebb1_predecessors.contains(&BasicBlock::new(ebb0, jmp_ebb0_ebb1)),
+                true
+            );
+            assert_eq!(
+                ebb1_predecessors.contains(&BasicBlock::new(ebb1, br_ebb1_ebb1)),
+                true
+            );
+            assert_eq!(
+                ebb2_predecessors.contains(&BasicBlock::new(ebb0, br_ebb0_ebb2)),
+                true
+            );
+            assert_eq!(
+                ebb2_predecessors.contains(&BasicBlock::new(ebb1, jmp_ebb1_ebb2)),
+                true
+            );
 
             assert_eq!(ebb0_successors, [ebb1, ebb2]);
             assert_eq!(ebb1_successors, [ebb1, ebb2]);
@@ -297,10 +322,22 @@ mod tests {
             assert_eq!(ebb1_predecessors.len(), 2);
             assert_eq!(ebb2_predecessors.len(), 1);
 
-            assert_eq!(ebb1_predecessors.contains(&(ebb0, br_ebb0_ebb1)), true);
-            assert_eq!(ebb1_predecessors.contains(&(ebb1, br_ebb1_ebb1)), true);
-            assert_eq!(ebb2_predecessors.contains(&(ebb0, br_ebb0_ebb2)), false);
-            assert_eq!(ebb2_predecessors.contains(&(ebb1, jmp_ebb1_ebb2)), true);
+            assert_eq!(
+                ebb1_predecessors.contains(&BasicBlock::new(ebb0, br_ebb0_ebb1)),
+                true
+            );
+            assert_eq!(
+                ebb1_predecessors.contains(&BasicBlock::new(ebb1, br_ebb1_ebb1)),
+                true
+            );
+            assert_eq!(
+                ebb2_predecessors.contains(&BasicBlock::new(ebb0, br_ebb0_ebb2)),
+                false
+            );
+            assert_eq!(
+                ebb2_predecessors.contains(&BasicBlock::new(ebb1, jmp_ebb1_ebb2)),
+                true
+            );
 
             assert_eq!(ebb0_successors.collect::<Vec<_>>(), [ebb1]);
             assert_eq!(ebb1_successors.collect::<Vec<_>>(), [ebb1, ebb2]);
diff --git a/lib/codegen/src/legalizer/split.rs b/lib/codegen/src/legalizer/split.rs
index bbb63397a5..a7cd37dc60 100644
--- a/lib/codegen/src/legalizer/split.rs
+++ b/lib/codegen/src/legalizer/split.rs
@@ -65,7 +65,7 @@
 //! instructions. These loops will remain in the program.
 
 use cursor::{Cursor, CursorPosition, FuncCursor};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir::{self, Ebb, Inst, InstBuilder, InstructionData, Opcode, Type, Value, ValueDef};
 use std::iter;
 use std::vec::Vec;
@@ -126,7 +126,7 @@ fn split_any(
 
     // We have split the value requested, and now we may need to fix some EBB predecessors.
     while let Some(repair) = repairs.pop() {
-        for (_, inst) in cfg.pred_iter(repair.ebb) {
+        for BasicBlock { inst, .. } in cfg.pred_iter(repair.ebb) {
             let branch_opc = pos.func.dfg[inst].opcode();
             debug_assert!(
                 branch_opc.is_branch(),
diff --git a/lib/codegen/src/licm.rs b/lib/codegen/src/licm.rs
index 8f32b640ac..f9954087b4 100644
--- a/lib/codegen/src/licm.rs
+++ b/lib/codegen/src/licm.rs
@@ -3,7 +3,7 @@
 use cursor::{Cursor, FuncCursor};
 use dominator_tree::DominatorTree;
 use entity::{EntityList, ListPool};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use fx::FxHashSet;
 use ir::{DataFlowGraph, Ebb, Function, Inst, InstBuilder, Layout, Opcode, Type, Value};
 use loop_analysis::{Loop, LoopAnalysis};
@@ -77,7 +77,10 @@ fn create_pre_header(
     for typ in header_args_types {
         pre_header_args_value.push(func.dfg.append_ebb_param(pre_header, typ), pool);
     }
-    for (_, last_inst) in cfg.pred_iter(header) {
+    for BasicBlock {
+        inst: last_inst, ..
+    } in cfg.pred_iter(header)
+    {
         // We only follow normal edges (not the back edges)
         if !domtree.dominates(header, last_inst, &func.layout) {
             change_branch_jump_destination(last_inst, pre_header, func);
@@ -106,7 +109,11 @@ fn has_pre_header(
 ) -> Option<(Ebb, Inst)> {
     let mut result = None;
     let mut found = false;
-    for (pred_ebb, last_inst) in cfg.pred_iter(header) {
+    for BasicBlock {
+        ebb: pred_ebb,
+        inst: last_inst,
+    } in cfg.pred_iter(header)
+    {
         // We only count normal edges (not the back edges)
         if !domtree.dominates(header, last_inst, layout) {
             if found {
diff --git a/lib/codegen/src/loop_analysis.rs b/lib/codegen/src/loop_analysis.rs
index c2c73bba3f..fc1591b0cf 100644
--- a/lib/codegen/src/loop_analysis.rs
+++ b/lib/codegen/src/loop_analysis.rs
@@ -4,7 +4,7 @@
 use dominator_tree::DominatorTree;
 use entity::EntityMap;
 use entity::{Keys, PrimaryMap};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir::{Ebb, Function, Layout};
 use packed_option::PackedOption;
 use std::vec::Vec;
@@ -137,7 +137,10 @@ impl LoopAnalysis {
     ) {
         // We traverse the CFG in reverse postorder
         for &ebb in domtree.cfg_postorder().iter().rev() {
-            for (_, pred_inst) in cfg.pred_iter(ebb) {
+            for BasicBlock {
+                inst: pred_inst, ..
+            } in cfg.pred_iter(ebb)
+            {
                 // If the ebb dominates one of its predecessors it is a back edge
                 if domtree.dominates(ebb, pred_inst, layout) {
                     // This ebb is a loop header, so we create its associated loop
@@ -163,7 +166,11 @@ impl LoopAnalysis {
         // We handle each loop header in reverse order, corresponding to a pseudo postorder
         // traversal of the graph.
         for lp in self.loops().rev() {
-            for (pred, pred_inst) in cfg.pred_iter(self.loops[lp].header) {
+            for BasicBlock {
+                ebb: pred,
+                inst: pred_inst,
+            } in cfg.pred_iter(self.loops[lp].header)
+            {
                 // We follow the back edges
                 if domtree.dominates(self.loops[lp].header, pred_inst, layout) {
                     stack.push(pred);
@@ -213,7 +220,7 @@ impl LoopAnalysis {
                 // Now we have handled the popped node and need to continue the DFS by adding the
                 // predecessors of that node
                 if let Some(continue_dfs) = continue_dfs {
-                    for (pred, _) in cfg.pred_iter(continue_dfs) {
+                    for BasicBlock { ebb: pred, .. } in cfg.pred_iter(continue_dfs) {
                         stack.push(pred)
                     }
                 }
diff --git a/lib/codegen/src/regalloc/coalescing.rs b/lib/codegen/src/regalloc/coalescing.rs
index dd77b41937..0f00730fb8 100644
--- a/lib/codegen/src/regalloc/coalescing.rs
+++ b/lib/codegen/src/regalloc/coalescing.rs
@@ -9,7 +9,7 @@ use cursor::{Cursor, EncCursor};
 #[cfg(feature = "std")]
 use dbg::DisplayList;
 use dominator_tree::{DominatorTree, DominatorTreePreorder};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use fx::FxHashMap;
 use ir::{self, InstBuilder, ProgramOrder};
 use ir::{Ebb, ExpandedProgramPoint, Function, Inst, Value};
@@ -174,7 +174,11 @@ impl<'a> Context<'a> {
         debug_assert_eq!(num_params, self.func.dfg.num_ebb_params(ebb));
         // The only way a parameter value can interfere with a predecessor branch is if the EBB is
         // dominating the predecessor branch. That is, we are looking for loop back-edges.
-        for (pred_ebb, pred_inst) in self.cfg.pred_iter(ebb) {
+        for BasicBlock {
+            ebb: pred_ebb,
+            inst: pred_inst,
+        } in self.cfg.pred_iter(ebb)
+        {
             // The quick pre-order dominance check is accurate because the EBB parameter is defined
             // at the top of the EBB before any branches.
             if !self.preorder.dominates(ebb, pred_ebb) {
@@ -211,7 +215,11 @@ impl<'a> Context<'a> {
     fn union_pred_args(&mut self, ebb: Ebb, argnum: usize) {
         let param = self.func.dfg.ebb_params(ebb)[argnum];
 
-        for (pred_ebb, pred_inst) in self.cfg.pred_iter(ebb) {
+        for BasicBlock {
+            ebb: pred_ebb,
+            inst: pred_inst,
+        } in self.cfg.pred_iter(ebb)
+        {
             let arg = self.func.dfg.inst_variable_args(pred_inst)[argnum];
 
             // Never coalesce incoming function parameters on the stack. These parameters are
@@ -484,7 +492,11 @@ impl<'a> Context<'a> {
         // not loop backedges.
         debug_assert!(self.predecessors.is_empty());
         debug_assert!(self.backedges.is_empty());
-        for (pred_ebb, pred_inst) in self.cfg.pred_iter(ebb) {
+        for BasicBlock {
+            ebb: pred_ebb,
+            inst: pred_inst,
+        } in self.cfg.pred_iter(ebb)
+        {
             if self.preorder.dominates(ebb, pred_ebb) {
                 self.backedges.push(pred_inst);
             } else {
@@ -915,7 +927,10 @@ impl VirtualCopies {
                 }
 
                 // This EBB hasn't been seen before.
-                for (_, pred_inst) in cfg.pred_iter(ebb) {
+                for BasicBlock {
+                    inst: pred_inst, ..
+                } in cfg.pred_iter(ebb)
+                {
                     self.branches.push((pred_inst, ebb));
                 }
                 last_ebb = Some(ebb);
diff --git a/lib/codegen/src/regalloc/liveness.rs b/lib/codegen/src/regalloc/liveness.rs
index 7f5ee4ae5d..d169acc459 100644
--- a/lib/codegen/src/regalloc/liveness.rs
+++ b/lib/codegen/src/regalloc/liveness.rs
@@ -176,7 +176,7 @@
 //! There is some room for improvement.
 
 use entity::SparseMap;
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir::dfg::ValueDef;
 use ir::{Ebb, Function, Inst, Layout, ProgramPoint, Value};
 use isa::{EncInfo, OperandConstraint, TargetIsa};
@@ -272,7 +272,11 @@ fn extend_to_use(
     while let Some(livein) = worklist.pop() {
         // We've learned that the value needs to be live-in to the `livein` EBB.
         // Make sure it is also live at all predecessor branches to `livein`.
-        for (pred, branch) in cfg.pred_iter(livein) {
+        for BasicBlock {
+            ebb: pred,
+            inst: branch,
+        } in cfg.pred_iter(livein)
+        {
             if lr.extend_in_ebb(pred, branch, &func.layout, forest) {
                 // This predecessor EBB also became live-in. We need to process it later.
                 worklist.push(pred);
diff --git a/lib/codegen/src/verifier/cssa.rs b/lib/codegen/src/verifier/cssa.rs
index 8e3402208b..c2d745c4fb 100644
--- a/lib/codegen/src/verifier/cssa.rs
+++ b/lib/codegen/src/verifier/cssa.rs
@@ -2,7 +2,7 @@
 
 use dbg::DisplayList;
 use dominator_tree::{DominatorTree, DominatorTreePreorder};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir::{ExpandedProgramPoint, Function};
 use regalloc::liveness::Liveness;
 use regalloc::virtregs::VirtRegs;
@@ -138,7 +138,7 @@ impl<'a> CssaVerifier<'a> {
     fn check_cssa(&self) -> VerifierResult<()> {
         for ebb in self.func.layout.ebbs() {
             let ebb_params = self.func.dfg.ebb_params(ebb);
-            for (_, pred) in self.cfg.pred_iter(ebb) {
+            for BasicBlock { inst: pred, .. } in self.cfg.pred_iter(ebb) {
                 let pred_args = self.func.dfg.inst_variable_args(pred);
                 // This should have been caught by an earlier verifier pass.
                 assert_eq!(
diff --git a/lib/codegen/src/verifier/flags.rs b/lib/codegen/src/verifier/flags.rs
index 05ce764310..04615bacd7 100644
--- a/lib/codegen/src/verifier/flags.rs
+++ b/lib/codegen/src/verifier/flags.rs
@@ -1,7 +1,7 @@
 //! Verify CPU flags values.
 
 use entity::{EntityMap, SparseSet};
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir;
 use ir::instructions::BranchInfo;
 use isa;
@@ -61,7 +61,7 @@ impl<'a> FlagsVerifier<'a> {
                     // Revisit any predecessor blocks the first time we see a live-in for `ebb`.
                     None => {
                         self.livein[ebb] = value.into();
-                        for (pred, _) in self.cfg.pred_iter(ebb) {
+                        for BasicBlock { ebb: pred, .. } in self.cfg.pred_iter(ebb) {
                             worklist.insert(pred);
                         }
                     }
diff --git a/lib/codegen/src/verifier/liveness.rs b/lib/codegen/src/verifier/liveness.rs
index e2bf6a21ef..f884feea79 100644
--- a/lib/codegen/src/verifier/liveness.rs
+++ b/lib/codegen/src/verifier/liveness.rs
@@ -1,6 +1,6 @@
 //! Liveness verifier.
 
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir::entities::AnyEntity;
 use ir::{ExpandedProgramPoint, Function, Inst, ProgramOrder, ProgramPoint, Value};
 use isa::TargetIsa;
@@ -194,7 +194,7 @@ impl<'a> LivenessVerifier<'a> {
             // Check all the EBBs in the interval independently.
             loop {
                 // If `val` is live-in at `ebb`, it must be live at all the predecessors.
-                for (_, pred) in self.cfg.pred_iter(ebb) {
+                for BasicBlock { inst: pred, .. } in self.cfg.pred_iter(ebb) {
                     if !self.live_at_use(lr, pred) {
                         return err!(
                             pred,
diff --git a/lib/codegen/src/verifier/mod.rs b/lib/codegen/src/verifier/mod.rs
index aa3923456c..f92bdda1d8 100644
--- a/lib/codegen/src/verifier/mod.rs
+++ b/lib/codegen/src/verifier/mod.rs
@@ -60,7 +60,7 @@ use self::flags::verify_flags;
 use dbg::DisplayList;
 use dominator_tree::DominatorTree;
 use entity::SparseSet;
-use flowgraph::ControlFlowGraph;
+use flowgraph::{BasicBlock, ControlFlowGraph};
 use ir;
 use ir::entities::AnyEntity;
 use ir::instructions::{BranchInfo, CallInfo, InstructionFormat, ResolvedConstraint};
@@ -990,8 +990,12 @@ impl<'a> Verifier<'a> {
                 return err!(ebb, "cfg had unexpected successor(s) {:?}", excess_succs);
             }
 
-            expected_preds.extend(self.expected_cfg.pred_iter(ebb).map(|(_, inst)| inst));
-            got_preds.extend(cfg.pred_iter(ebb).map(|(_, inst)| inst));
+            expected_preds.extend(
+                self.expected_cfg
+                    .pred_iter(ebb)
+                    .map(|BasicBlock { inst, .. }| inst),
+            );
+            got_preds.extend(cfg.pred_iter(ebb).map(|BasicBlock { inst, .. }| inst));
 
             let missing_preds: Vec<Inst> = expected_preds.difference(&got_preds).cloned().collect();
             if !missing_preds.is_empty() {