diff --git a/lib/cretonne/src/regalloc/affinity.rs b/lib/cretonne/src/regalloc/affinity.rs
index f6ca587485..64d2b640df 100644
--- a/lib/cretonne/src/regalloc/affinity.rs
+++ b/lib/cretonne/src/regalloc/affinity.rs
@@ -15,8 +15,11 @@ use isa::{TargetIsa, RegInfo, RegClassIndex, OperandConstraint, ConstraintKind};
 /// Preferred register allocation for an SSA value.
 #[derive(Clone, Copy)]
 pub enum Affinity {
-    /// Don't care. This value can go anywhere.
-    Any,
+    /// No affinity.
+    ///
+    /// This indicates a value that is not defined or used by any real instructions. It is a ghost
+    /// value that won't appear in the final program.
+    None,
 
     /// This value should be placed in a spill slot on the stack.
     Stack,
@@ -27,14 +30,14 @@ pub enum Affinity {
 
 impl Default for Affinity {
     fn default() -> Self {
-        Affinity::Any
+        Affinity::None
     }
 }
 
 impl Affinity {
     /// Create an affinity that satisfies a single constraint.
     ///
-    /// This will never create the indifferent `Affinity::Any`.
+    /// This will never create an `Affinity::None`.
     /// Use the `Default` implementation for that.
     pub fn new(constraint: &OperandConstraint) -> Affinity {
         if constraint.kind == ConstraintKind::Stack {
@@ -47,19 +50,27 @@ impl Affinity {
     /// Create an affinity that matches an ABI argument for `isa`.
     pub fn abi(arg: &ArgumentType, isa: &TargetIsa) -> Affinity {
         match arg.location {
-            ArgumentLoc::Unassigned => Affinity::Any,
+            ArgumentLoc::Unassigned => Affinity::None,
             ArgumentLoc::Reg(_) => Affinity::Reg(isa.regclass_for_abi_type(arg.value_type).into()),
             ArgumentLoc::Stack(_) => Affinity::Stack,
         }
     }
 
+    /// Is this the `None` affinity?
+    pub fn is_none(self) -> bool {
+        match self {
+            Affinity::None => true,
+            _ => false,
+        }
+    }
+
     /// Merge an operand constraint into this affinity.
     ///
     /// Note that this does not guarantee that the register allocator will pick a register that
     /// satisfies the constraint.
     pub fn merge(&mut self, constraint: &OperandConstraint, reg_info: &RegInfo) {
         match *self {
-            Affinity::Any => *self = Affinity::new(constraint),
+            Affinity::None => *self = Affinity::new(constraint),
             Affinity::Reg(rc) => {
                 // If the preferred register class is a subclass of the constraint, there's no need
                 // to change anything.
diff --git a/lib/cretonne/src/regalloc/coloring.rs b/lib/cretonne/src/regalloc/coloring.rs
index b9e5fe7148..84e81660d7 100644
--- a/lib/cretonne/src/regalloc/coloring.rs
+++ b/lib/cretonne/src/regalloc/coloring.rs
@@ -327,7 +327,9 @@ impl<'a> Context<'a> {
                     }
                 }
                 Affinity::Stack => unimplemented!(),
-                Affinity::Any => unimplemented!(),
+                Affinity::None => {
+                    panic!("Encoded instruction defines {} with no affinity", lv.value)
+                }
             }
         }
 
diff --git a/lib/cretonne/src/verifier/liveness.rs b/lib/cretonne/src/verifier/liveness.rs
index d80f18a8b3..d3d841b68e 100644
--- a/lib/cretonne/src/verifier/liveness.rs
+++ b/lib/cretonne/src/verifier/liveness.rs
@@ -21,12 +21,13 @@ use verifier::Result;
 ///
 /// We don't verify that live ranges are minimal. This would require recomputing live ranges for
 /// all values.
-pub fn verify_liveness(_isa: &TargetIsa,
+pub fn verify_liveness(isa: &TargetIsa,
                        func: &Function,
                        cfg: &ControlFlowGraph,
                        liveness: &Liveness)
                        -> Result {
     let verifier = LivenessVerifier {
+        isa: isa,
         func: func,
         cfg: cfg,
         liveness: liveness,
@@ -37,6 +38,7 @@ pub fn verify_liveness(_isa: &TargetIsa,
 }
 
 struct LivenessVerifier<'a> {
+    isa: &'a TargetIsa,
     func: &'a Function,
     cfg: &'a ControlFlowGraph,
     liveness: &'a Liveness,
@@ -61,6 +63,8 @@ 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);
+
                 // Check the defs.
                 for &val in self.func.dfg.inst_results(inst) {
                     let lr = match self.liveness.get(val) {
@@ -68,6 +72,24 @@ impl<'a> LivenessVerifier<'a> {
                         None => return err!(inst, "{} has no live range", val),
                     };
                     self.check_lr(inst.into(), val, lr)?;
+
+                    if encoding.is_legal() {
+                        // A legal instruction is not allowed to define ghost values.
+                        if lr.affinity.is_none() {
+                            return err!(inst,
+                                        "{} is a ghost value defined by a real [{}] instruction",
+                                        val,
+                                        self.isa.encoding_info().display(encoding));
+                        }
+                    } else {
+                        // A non-encoded instruction can only define ghost values.
+                        if !lr.affinity.is_none() {
+                            return err!(inst,
+                                        "{} is a real {} value defined by a ghost instruction",
+                                        val,
+                                        lr.affinity.display(&self.isa.register_info()));
+                        }
+                    }
                 }
 
                 // Check the uses.
@@ -79,6 +101,16 @@ impl<'a> LivenessVerifier<'a> {
                     if !self.live_at_use(lr, inst) {
                         return err!(inst, "{} is not live at this use", val);
                     }
+
+                    if encoding.is_legal() {
+                        // A legal instruction is not allowed to depend on ghost values.
+                        if lr.affinity.is_none() {
+                            return err!(inst,
+                                        "{} is a ghost value used by a real [{}] instruction",
+                                        val,
+                                        self.isa.encoding_info().display(encoding));
+                        }
+                    }
                 }
             }
         }