diff --git a/cranelift/codegen/src/machinst/reg.rs b/cranelift/codegen/src/machinst/reg.rs
index 4a550d3fa36d..2705c74c90a0 100644
--- a/cranelift/codegen/src/machinst/reg.rs
+++ b/cranelift/codegen/src/machinst/reg.rs
@@ -293,24 +293,10 @@ pub struct OperandCollector<'a, 'env, F: Fn(VReg) -> VReg> {
     renamer: F,
 }
 
-macro_rules! debug_assert_allocatable {
-    ($env:expr, $reg:expr) => {
-        if cfg!(debug_assertions) {
-            let class = $reg.class() as usize;
-            if let Some(reg) = pinned_vreg_to_preg($reg) {
-                assert!(
-                    $env.preferred_regs_by_class[class]
-                        .iter()
-                        .copied()
-                        .any(|r| r == reg)
-                        || $env.non_preferred_regs_by_class[class]
-                            .iter()
-                            .copied()
-                            .any(|r| r == reg)
-                );
-            }
-        }
-    };
+macro_rules! debug_assert_is_virtual {
+    ($reg:expr) => {
+        debug_assert!($reg.is_virtual(), "`{:?}` was used, but is not virtual", $reg);
+    }
 }
 
 impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
@@ -326,6 +312,22 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
         }
     }
 
+    pub fn is_allocatable_preg(&self, reg: PReg) -> bool {
+        let class = reg.class() as usize;
+        self.machine_env.preferred_regs_by_class[class]
+            .iter()
+            .copied()
+            .any(|r| r == reg)
+            || self.machine_env.non_preferred_regs_by_class[class]
+                .iter()
+                .copied()
+                .any(|r| r == reg)
+    }
+
+    pub fn is_allocatable_reg(&self, reg: Reg) -> bool {
+        pinned_vreg_to_preg(reg.0).map_or(false, |preg| self.is_allocatable_preg(preg))
+    }
+
     /// Add an operand.
     fn add_operand(&mut self, operand: Operand) {
         let vreg = (self.renamer)(operand.vreg());
@@ -345,17 +347,20 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// Add a register use, at the start of the instruction (`Before`
     /// position).
     pub fn reg_use(&mut self, reg: Reg) {
+        debug_assert_is_virtual!(reg);
         self.add_operand(Operand::reg_use(reg.into()));
     }
 
     /// Add a register use, at the end of the instruction (`After` position).
     pub fn reg_late_use(&mut self, reg: Reg) {
+        debug_assert_is_virtual!(reg);
         self.add_operand(Operand::reg_use_at_end(reg.into()));
     }
 
     /// Add multiple register uses.
     pub fn reg_uses(&mut self, regs: &[Reg]) {
         for &reg in regs {
+            debug_assert_is_virtual!(reg);
             self.reg_use(reg);
         }
     }
@@ -364,12 +369,14 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// position). Use only when this def will be written after all
     /// uses are read.
     pub fn reg_def(&mut self, reg: Writable<Reg>) {
+        debug_assert_is_virtual!(reg.to_reg());
         self.add_operand(Operand::reg_def(reg.to_reg().into()));
     }
 
     /// Add multiple register defs.
     pub fn reg_defs(&mut self, regs: &[Writable<Reg>]) {
         for &reg in regs {
+            debug_assert_is_virtual!(reg.to_reg());
             self.reg_def(reg);
         }
     }
@@ -379,13 +386,15 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// when the def may be written before all uses are read; the
     /// regalloc will ensure that it does not overwrite any uses.
     pub fn reg_early_def(&mut self, reg: Writable<Reg>) {
+        debug_assert_is_virtual!(reg.to_reg());
         self.add_operand(Operand::reg_def_at_start(reg.to_reg().into()));
     }
 
     /// Add a register "fixed use", which ties a vreg to a particular
     /// RealReg at this point.
     pub fn reg_fixed_use(&mut self, reg: Reg, rreg: Reg) {
-        debug_assert_allocatable!(self.machine_env, rreg.0);
+        debug_assert_is_virtual!(reg);
+        debug_assert!(self.is_allocatable_reg(rreg));
         let rreg = rreg.to_real_reg().expect("fixed reg is not a RealReg");
         self.add_operand(Operand::reg_fixed_use(reg.into(), rreg.into()));
     }
@@ -393,7 +402,8 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// Add a register "fixed def", which ties a vreg to a particular
     /// RealReg at this point.
     pub fn reg_fixed_def(&mut self, reg: Writable<Reg>, rreg: Reg) {
-        debug_assert_allocatable!(self.machine_env, rreg.0);
+        debug_assert_is_virtual!(reg.to_reg());
+        debug_assert!(self.is_allocatable_reg(rreg));
         let rreg = rreg.to_real_reg().expect("fixed reg is not a RealReg");
         self.add_operand(Operand::reg_fixed_def(reg.to_reg().into(), rreg.into()));
     }
@@ -402,6 +412,7 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// allocation. The index of that earlier operand (relative to the
     /// current instruction's start of operands) must be known.
     pub fn reg_reuse_def(&mut self, reg: Writable<Reg>, idx: usize) {
+        debug_assert_is_virtual!(reg.to_reg());
         if reg.to_reg().to_virtual_reg().is_some() {
             self.add_operand(Operand::reg_reuse_def(reg.to_reg().into(), idx));
         } else {
@@ -417,6 +428,11 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// are written by the instruction, so must be reserved (not used)
     /// for the whole instruction, but are not used afterward.
     pub fn reg_clobbers(&mut self, regs: PRegSet) {
+        if cfg!(debug_assertions) {
+            for reg in regs.clone() {
+                debug_assert!(self.is_allocatable_preg(reg));
+            }
+        }
         self.clobbers.union_from(regs);
     }
 }