diff --git a/src/ion/liveranges.rs b/src/ion/liveranges.rs
index 5a9b00e4..e226884b 100644
--- a/src/ion/liveranges.rs
+++ b/src/ion/liveranges.rs
@@ -577,7 +577,7 @@ impl<'a, F: Function> Env<'a, F> {
                                 if late_def_fixed.contains(&preg)
                                     || self.func.inst_clobbers(inst).contains(preg)
                                 {
-                                    log::trace!(
+                                    trace!(
                                         concat!(
                                             "-> operand {:?} is fixed to preg {:?}, ",
                                             "is downward live, and there is also a ",
diff --git a/src/lib.rs b/src/lib.rs
index 070608ca..4185530b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -125,7 +125,7 @@ impl PReg {
     /// The register class.
     #[inline(always)]
     pub const fn class(self) -> RegClass {
-        match self.bits & (0b11 << Self::MAX_BITS) {
+        match (self.bits >> Self::MAX_BITS) & 0b11 {
             0 => RegClass::Int,
             1 => RegClass::Float,
             2 => RegClass::Vector,
@@ -188,49 +188,54 @@ impl core::fmt::Display for PReg {
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
 pub struct PRegSet {
-    bits: u128,
+    bits: [u128; 2],
 }
 
 impl PRegSet {
     /// Create an empty set.
     pub const fn empty() -> Self {
-        Self { bits: 0 }
+        Self { bits: [0; 2] }
     }
 
     /// Returns whether the given register is part of the set.
     pub fn contains(&self, reg: PReg) -> bool {
-        let bit = reg.index();
-        debug_assert!(bit < 128);
-        self.bits & 1u128 << bit != 0
+        debug_assert!(reg.index() < 256);
+        let bit = reg.index() & 127;
+        let index = reg.index() >> 7;
+        self.bits[index] & (1u128 << bit) != 0
     }
 
     /// Add a physical register (PReg) to the set, returning the new value.
     pub const fn with(self, reg: PReg) -> Self {
-        let bit = reg.index();
-        debug_assert!(bit < 128);
-        Self {
-            bits: self.bits | (1u128 << bit),
-        }
+        debug_assert!(reg.index() < 256);
+        let bit = reg.index() & 127;
+        let index = reg.index() >> 7;
+        let mut out = self;
+        out.bits[index] |= 1u128 << bit;
+        out
     }
 
     /// Add a physical register (PReg) to the set.
     pub fn add(&mut self, reg: PReg) {
-        let bit = reg.index();
-        debug_assert!(bit < 128);
-        self.bits |= 1u128 << bit;
+        debug_assert!(reg.index() < 256);
+        let bit = reg.index() & 127;
+        let index = reg.index() >> 7;
+        self.bits[index] |= 1u128 << bit;
     }
 
     /// Remove a physical register (PReg) from the set.
     pub fn remove(&mut self, reg: PReg) {
-        let bit = reg.index();
-        debug_assert!(bit < 128);
-        self.bits &= !(1u128 << bit);
+        debug_assert!(reg.index() < 256);
+        let bit = reg.index() & 127;
+        let index = reg.index() >> 7;
+        self.bits[index] &= !(1u128 << bit);
     }
 
     /// Add all of the registers in one set to this one, mutating in
     /// place.
     pub fn union_from(&mut self, other: PRegSet) {
-        self.bits |= other.bits;
+        self.bits[0] |= other.bits[0];
+        self.bits[1] |= other.bits[1];
     }
 }
 
@@ -243,18 +248,22 @@ impl IntoIterator for PRegSet {
 }
 
 pub struct PRegSetIter {
-    bits: u128,
+    bits: [u128; 2],
 }
 
 impl Iterator for PRegSetIter {
     type Item = PReg;
     fn next(&mut self) -> Option<PReg> {
-        if self.bits == 0 {
-            None
-        } else {
-            let index = self.bits.trailing_zeros();
-            self.bits &= !(1u128 << index);
+        if self.bits[0] != 0 {
+            let index = self.bits[0].trailing_zeros();
+            self.bits[0] &= !(1u128 << index);
             Some(PReg::from_index(index as usize))
+        } else if self.bits[1] != 0 {
+            let index = self.bits[1].trailing_zeros();
+            self.bits[1] &= !(1u128 << index);
+            Some(PReg::from_index(index as usize + 128))
+        } else {
+            None
         }
     }
 }
@@ -822,6 +831,9 @@ impl core::fmt::Debug for Operand {
 
 impl core::fmt::Display for Operand {
     fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        if let Some(preg) = self.as_fixed_nonallocatable() {
+            return write!(f, "Fixed: {preg}");
+        }
         match (self.kind(), self.pos()) {
             (OperandKind::Def, OperandPos::Late) | (OperandKind::Use, OperandPos::Early) => {
                 write!(f, "{:?}", self.kind())?;