diff --git a/cranelift/codegen/src/isa/aarch64/inst/emit.rs b/cranelift/codegen/src/isa/aarch64/inst/emit.rs
index 0784cdeb01..d2277b4ba6 100644
--- a/cranelift/codegen/src/isa/aarch64/inst/emit.rs
+++ b/cranelift/codegen/src/isa/aarch64/inst/emit.rs
@@ -1369,6 +1369,7 @@ impl MachInstEmit for Inst {
             }
             &Inst::MovFromPReg { rd, rm } => {
                 let rd = allocs.next_writable(rd);
+                allocs.next_fixed_nonallocatable(rm);
                 let rm: Reg = rm.into();
                 debug_assert!([
                     regs::fp_reg(),
@@ -1383,6 +1384,7 @@ impl MachInstEmit for Inst {
                 Inst::Mov { size, rd, rm }.emit(&[], sink, emit_info, state);
             }
             &Inst::MovToPReg { rd, rm } => {
+                allocs.next_fixed_nonallocatable(rd);
                 let rd: Writable<Reg> = Writable::from_reg(rd.into());
                 let rm = allocs.next(rm);
                 debug_assert!([
diff --git a/cranelift/codegen/src/isa/aarch64/inst/mod.rs b/cranelift/codegen/src/isa/aarch64/inst/mod.rs
index 29aeafc0ad..7e7c76f573 100644
--- a/cranelift/codegen/src/isa/aarch64/inst/mod.rs
+++ b/cranelift/codegen/src/isa/aarch64/inst/mod.rs
@@ -655,25 +655,13 @@ fn aarch64_get_operands<F: Fn(VReg) -> VReg>(inst: &Inst, collector: &mut Operan
             collector.reg_use(rm);
         }
         &Inst::MovFromPReg { rd, rm } => {
-            debug_assert!([
-                regs::fp_reg(),
-                regs::stack_reg(),
-                regs::link_reg(),
-                regs::pinned_reg()
-            ]
-            .contains(&rm.into()));
             debug_assert!(rd.to_reg().is_virtual());
             collector.reg_def(rd);
+            collector.reg_fixed_nonallocatable(rm);
         }
         &Inst::MovToPReg { rd, rm } => {
-            debug_assert!([
-                regs::fp_reg(),
-                regs::stack_reg(),
-                regs::link_reg(),
-                regs::pinned_reg()
-            ]
-            .contains(&rd.into()));
             debug_assert!(rm.is_virtual());
+            collector.reg_fixed_nonallocatable(rd);
             collector.reg_use(rm);
         }
         &Inst::MovK { rd, rn, .. } => {
@@ -1568,10 +1556,12 @@ impl Inst {
             }
             &Inst::MovFromPReg { rd, rm } => {
                 let rd = pretty_print_ireg(rd.to_reg(), OperandSize::Size64, allocs);
+                allocs.next_fixed_nonallocatable(rm);
                 let rm = show_ireg_sized(rm.into(), OperandSize::Size64);
                 format!("mov {}, {}", rd, rm)
             }
             &Inst::MovToPReg { rd, rm } => {
+                allocs.next_fixed_nonallocatable(rd);
                 let rd = show_ireg_sized(rd.into(), OperandSize::Size64);
                 let rm = pretty_print_ireg(rm, OperandSize::Size64, allocs);
                 format!("mov {}, {}", rd, rm)
diff --git a/cranelift/codegen/src/isa/aarch64/mod.rs b/cranelift/codegen/src/isa/aarch64/mod.rs
index 445dddfce3..72459c89e9 100644
--- a/cranelift/codegen/src/isa/aarch64/mod.rs
+++ b/cranelift/codegen/src/isa/aarch64/mod.rs
@@ -57,20 +57,11 @@ impl AArch64Backend {
     fn compile_vcode(
         &self,
         func: &Function,
-        flags: shared_settings::Flags,
     ) -> CodegenResult<(VCode<inst::Inst>, regalloc2::Output)> {
-        let emit_info = EmitInfo::new(flags.clone());
+        let emit_info = EmitInfo::new(self.flags.clone());
         let sigs = SigSet::new::<abi::AArch64MachineDeps>(func, &self.flags)?;
         let abi = abi::AArch64Callee::new(func, self, &self.isa_flags, &sigs)?;
-        compile::compile::<AArch64Backend>(
-            func,
-            flags,
-            self,
-            abi,
-            &self.machine_env,
-            emit_info,
-            sigs,
-        )
+        compile::compile::<AArch64Backend>(func, self, abi, emit_info, sigs)
     }
 }
 
@@ -80,10 +71,13 @@ impl TargetIsa for AArch64Backend {
         func: &Function,
         want_disasm: bool,
     ) -> CodegenResult<CompiledCodeStencil> {
-        let flags = self.flags();
-        let (vcode, regalloc_result) = self.compile_vcode(func, flags.clone())?;
+        let (vcode, regalloc_result) = self.compile_vcode(func)?;
 
-        let emit_result = vcode.emit(&regalloc_result, want_disasm, flags.machine_code_cfg_info());
+        let emit_result = vcode.emit(
+            &regalloc_result,
+            want_disasm,
+            self.flags.machine_code_cfg_info(),
+        );
         let frame_size = emit_result.frame_size;
         let value_labels_ranges = emit_result.value_labels_ranges;
         let buffer = emit_result.buffer.finish();
@@ -119,6 +113,10 @@ impl TargetIsa for AArch64Backend {
         &self.flags
     }
 
+    fn machine_env(&self) -> &MachineEnv {
+        &self.machine_env
+    }
+
     fn isa_flags(&self) -> Vec<shared_settings::Value> {
         self.isa_flags.iter().collect()
     }
diff --git a/cranelift/codegen/src/isa/mod.rs b/cranelift/codegen/src/isa/mod.rs
index c319433f5d..68fef2da6f 100644
--- a/cranelift/codegen/src/isa/mod.rs
+++ b/cranelift/codegen/src/isa/mod.rs
@@ -227,6 +227,9 @@ pub trait TargetIsa: fmt::Display + Send + Sync {
     /// Get the ISA-independent flags that were used to make this trait object.
     fn flags(&self) -> &settings::Flags;
 
+    /// Get the ISA-dependent MachineEnv for managing register allocation.
+    fn machine_env(&self) -> &regalloc2::MachineEnv;
+
     /// Get the ISA-dependent flag values that were used to make this trait object.
     fn isa_flags(&self) -> Vec<settings::Value>;
 
diff --git a/cranelift/codegen/src/isa/riscv64/mod.rs b/cranelift/codegen/src/isa/riscv64/mod.rs
index ffff098611..5f10175514 100644
--- a/cranelift/codegen/src/isa/riscv64/mod.rs
+++ b/cranelift/codegen/src/isa/riscv64/mod.rs
@@ -57,12 +57,11 @@ impl Riscv64Backend {
     fn compile_vcode(
         &self,
         func: &Function,
-        flags: shared_settings::Flags,
     ) -> CodegenResult<(VCode<inst::Inst>, regalloc2::Output)> {
-        let emit_info = EmitInfo::new(flags.clone(), self.isa_flags.clone());
+        let emit_info = EmitInfo::new(self.flags.clone(), self.isa_flags.clone());
         let sigs = SigSet::new::<abi::Riscv64MachineDeps>(func, &self.flags)?;
         let abi = abi::Riscv64Callee::new(func, self, &self.isa_flags, &sigs)?;
-        compile::compile::<Riscv64Backend>(func, flags, self, abi, &self.mach_env, emit_info, sigs)
+        compile::compile::<Riscv64Backend>(func, self, abi, emit_info, sigs)
     }
 }
 
@@ -72,11 +71,14 @@ impl TargetIsa for Riscv64Backend {
         func: &Function,
         want_disasm: bool,
     ) -> CodegenResult<CompiledCodeStencil> {
-        let flags = self.flags();
-        let (vcode, regalloc_result) = self.compile_vcode(func, flags.clone())?;
+        let (vcode, regalloc_result) = self.compile_vcode(func)?;
 
         let want_disasm = want_disasm || log::log_enabled!(log::Level::Debug);
-        let emit_result = vcode.emit(&regalloc_result, want_disasm, flags.machine_code_cfg_info());
+        let emit_result = vcode.emit(
+            &regalloc_result,
+            want_disasm,
+            self.flags.machine_code_cfg_info(),
+        );
         let frame_size = emit_result.frame_size;
         let value_labels_ranges = emit_result.value_labels_ranges;
         let buffer = emit_result.buffer.finish();
@@ -115,6 +117,10 @@ impl TargetIsa for Riscv64Backend {
         &self.flags
     }
 
+    fn machine_env(&self) -> &MachineEnv {
+        &self.mach_env
+    }
+
     fn isa_flags(&self) -> Vec<shared_settings::Value> {
         self.isa_flags.iter().collect()
     }
diff --git a/cranelift/codegen/src/isa/s390x/mod.rs b/cranelift/codegen/src/isa/s390x/mod.rs
index a10ad17bef..cc45c5c012 100644
--- a/cranelift/codegen/src/isa/s390x/mod.rs
+++ b/cranelift/codegen/src/isa/s390x/mod.rs
@@ -60,15 +60,7 @@ impl S390xBackend {
         let emit_info = EmitInfo::new(self.isa_flags.clone());
         let sigs = SigSet::new::<abi::S390xMachineDeps>(func, &self.flags)?;
         let abi = abi::S390xCallee::new(func, self, &self.isa_flags, &sigs)?;
-        compile::compile::<S390xBackend>(
-            func,
-            self.flags.clone(),
-            self,
-            abi,
-            &self.machine_env,
-            emit_info,
-            sigs,
-        )
+        compile::compile::<S390xBackend>(func, self, abi, emit_info, sigs)
     }
 }
 
@@ -117,6 +109,10 @@ impl TargetIsa for S390xBackend {
         &self.flags
     }
 
+    fn machine_env(&self) -> &MachineEnv {
+        &self.machine_env
+    }
+
     fn isa_flags(&self) -> Vec<shared_settings::Value> {
         self.isa_flags.iter().collect()
     }
diff --git a/cranelift/codegen/src/isa/x64/inst/emit.rs b/cranelift/codegen/src/isa/x64/inst/emit.rs
index 32f284a8c0..d773ae3816 100644
--- a/cranelift/codegen/src/isa/x64/inst/emit.rs
+++ b/cranelift/codegen/src/isa/x64/inst/emit.rs
@@ -699,6 +699,7 @@ pub(crate) fn emit(
         }
 
         Inst::MovFromPReg { src, dst } => {
+            allocs.next_fixed_nonallocatable(*src);
             let src: Reg = (*src).into();
             debug_assert!([regs::rsp(), regs::rbp(), regs::pinned_reg()].contains(&src));
             let src = Gpr::new(src).unwrap();
@@ -711,6 +712,7 @@ pub(crate) fn emit(
         Inst::MovToPReg { src, dst } => {
             let src = allocs.next(src.to_reg());
             let src = Gpr::new(src).unwrap();
+            allocs.next_fixed_nonallocatable(*dst);
             let dst: Reg = (*dst).into();
             debug_assert!([regs::rsp(), regs::rbp(), regs::pinned_reg()].contains(&dst));
             let dst = WritableGpr::from_writable_reg(Writable::from_reg(dst)).unwrap();
diff --git a/cranelift/codegen/src/isa/x64/inst/mod.rs b/cranelift/codegen/src/isa/x64/inst/mod.rs
index 6ee5e7a26a..34a9df84ae 100644
--- a/cranelift/codegen/src/isa/x64/inst/mod.rs
+++ b/cranelift/codegen/src/isa/x64/inst/mod.rs
@@ -1263,6 +1263,7 @@ impl PrettyPrint for Inst {
             }
 
             Inst::MovFromPReg { src, dst } => {
+                allocs.next_fixed_nonallocatable(*src);
                 let src: Reg = (*src).into();
                 let src = regs::show_ireg_sized(src, 8);
                 let dst = pretty_print_reg(dst.to_reg().to_reg(), 8, allocs);
@@ -1271,6 +1272,7 @@ impl PrettyPrint for Inst {
 
             Inst::MovToPReg { src, dst } => {
                 let src = pretty_print_reg(src.to_reg(), 8, allocs);
+                allocs.next_fixed_nonallocatable(*dst);
                 let dst: Reg = (*dst).into();
                 let dst = regs::show_ireg_sized(dst, 8);
                 format!("{} {}, {}", ljustify("movq".to_string()), src, dst)
@@ -1919,14 +1921,14 @@ fn x64_get_operands<F: Fn(VReg) -> VReg>(inst: &Inst, collector: &mut OperandCol
             collector.reg_def(dst.to_writable_reg());
         }
         Inst::MovFromPReg { dst, src } => {
-            debug_assert!([regs::rsp(), regs::rbp(), regs::pinned_reg()].contains(&(*src).into()));
             debug_assert!(dst.to_reg().to_reg().is_virtual());
+            collector.reg_fixed_nonallocatable(*src);
             collector.reg_def(dst.to_writable_reg());
         }
         Inst::MovToPReg { dst, src } => {
             debug_assert!(src.to_reg().is_virtual());
-            debug_assert!([regs::rsp(), regs::rbp(), regs::pinned_reg()].contains(&(*dst).into()));
             collector.reg_use(src.to_reg());
+            collector.reg_fixed_nonallocatable(*dst);
         }
         Inst::XmmToGpr { src, dst, .. } => {
             collector.reg_use(src.to_reg());
diff --git a/cranelift/codegen/src/isa/x64/mod.rs b/cranelift/codegen/src/isa/x64/mod.rs
index 30d553ead8..a947e00f07 100644
--- a/cranelift/codegen/src/isa/x64/mod.rs
+++ b/cranelift/codegen/src/isa/x64/mod.rs
@@ -48,14 +48,13 @@ impl X64Backend {
     fn compile_vcode(
         &self,
         func: &Function,
-        flags: Flags,
     ) -> CodegenResult<(VCode<inst::Inst>, regalloc2::Output)> {
         // This performs lowering to VCode, register-allocates the code, computes
         // block layout and finalizes branches. The result is ready for binary emission.
-        let emit_info = EmitInfo::new(flags.clone(), self.x64_flags.clone());
+        let emit_info = EmitInfo::new(self.flags.clone(), self.x64_flags.clone());
         let sigs = SigSet::new::<abi::X64ABIMachineSpec>(func, &self.flags)?;
         let abi = abi::X64Callee::new(&func, self, &self.x64_flags, &sigs)?;
-        compile::compile::<Self>(&func, flags, self, abi, &self.reg_env, emit_info, sigs)
+        compile::compile::<Self>(&func, self, abi, emit_info, sigs)
     }
 }
 
@@ -65,10 +64,13 @@ impl TargetIsa for X64Backend {
         func: &Function,
         want_disasm: bool,
     ) -> CodegenResult<CompiledCodeStencil> {
-        let flags = self.flags();
-        let (vcode, regalloc_result) = self.compile_vcode(func, flags.clone())?;
+        let (vcode, regalloc_result) = self.compile_vcode(func)?;
 
-        let emit_result = vcode.emit(&regalloc_result, want_disasm, flags.machine_code_cfg_info());
+        let emit_result = vcode.emit(
+            &regalloc_result,
+            want_disasm,
+            self.flags.machine_code_cfg_info(),
+        );
         let frame_size = emit_result.frame_size;
         let value_labels_ranges = emit_result.value_labels_ranges;
         let buffer = emit_result.buffer.finish();
@@ -96,6 +98,10 @@ impl TargetIsa for X64Backend {
         &self.flags
     }
 
+    fn machine_env(&self) -> &MachineEnv {
+        &self.reg_env
+    }
+
     fn isa_flags(&self) -> Vec<shared_settings::Value> {
         self.x64_flags.iter().collect()
     }
diff --git a/cranelift/codegen/src/machinst/compile.rs b/cranelift/codegen/src/machinst/compile.rs
index a140842a90..bf773eb30a 100644
--- a/cranelift/codegen/src/machinst/compile.rs
+++ b/cranelift/codegen/src/machinst/compile.rs
@@ -7,24 +7,31 @@ use crate::timing;
 use crate::trace;
 
 use regalloc2::RegallocOptions;
-use regalloc2::{self, MachineEnv};
 
 /// Compile the given function down to VCode with allocated registers, ready
 /// for binary emission.
 pub fn compile<B: LowerBackend + TargetIsa>(
     f: &Function,
-    flags: crate::settings::Flags,
     b: &B,
     abi: Callee<<<B as LowerBackend>::MInst as MachInst>::ABIMachineSpec>,
-    machine_env: &MachineEnv,
     emit_info: <B::MInst as MachInstEmit>::Info,
     sigs: SigSet,
 ) -> CodegenResult<(VCode<B::MInst>, regalloc2::Output)> {
+    let machine_env = b.machine_env();
+
     // Compute lowered block order.
     let block_order = BlockLoweringOrder::new(f);
 
     // Build the lowering context.
-    let lower = crate::machinst::Lower::new(f, flags, abi, emit_info, block_order, sigs)?;
+    let lower = crate::machinst::Lower::new(
+        f,
+        b.flags().clone(),
+        machine_env,
+        abi,
+        emit_info,
+        block_order,
+        sigs,
+    )?;
 
     // Lower the IR.
     let vcode = {
diff --git a/cranelift/codegen/src/machinst/lower.rs b/cranelift/codegen/src/machinst/lower.rs
index e09b5585c8..97fcf909eb 100644
--- a/cranelift/codegen/src/machinst/lower.rs
+++ b/cranelift/codegen/src/machinst/lower.rs
@@ -21,10 +21,11 @@ use crate::machinst::{
 };
 use crate::{trace, CodegenResult};
 use alloc::vec::Vec;
+use regalloc2::{MachineEnv, PRegSet};
 use smallvec::{smallvec, SmallVec};
 use std::fmt::Debug;
 
-use super::{VCodeBuildDirection, VRegAllocator};
+use super::{preg_set_from_machine_env, VCodeBuildDirection, VRegAllocator};
 
 /// An "instruction color" partitions CLIF instructions by side-effecting ops.
 /// All instructions with the same "color" are guaranteed not to be separated by
@@ -149,6 +150,9 @@ pub struct Lower<'func, I: VCodeInst> {
     /// Machine-independent flags.
     flags: crate::settings::Flags,
 
+    /// The set of allocatable registers.
+    allocatable: PRegSet,
+
     /// Lowered machine instructions.
     vcode: VCodeBuilder<I>,
 
@@ -322,11 +326,12 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
     pub fn new(
         f: &'func Function,
         flags: crate::settings::Flags,
+        machine_env: &MachineEnv,
         abi: Callee<I::ABIMachineSpec>,
         emit_info: I::Info,
         block_order: BlockLoweringOrder,
         sigs: SigSet,
-    ) -> CodegenResult<Lower<'func, I>> {
+    ) -> CodegenResult<Self> {
         let constants = VCodeConstants::with_capacity(f.dfg.constants.len());
         let vcode = VCodeBuilder::new(
             sigs,
@@ -412,6 +417,7 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
         Ok(Lower {
             f,
             flags,
+            allocatable: preg_set_from_machine_env(machine_env),
             vcode,
             vregs,
             value_regs,
@@ -1019,7 +1025,7 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
 
         // Now that we've emitted all instructions into the
         // VCodeBuilder, let's build the VCode.
-        let vcode = self.vcode.build(self.vregs);
+        let vcode = self.vcode.build(self.allocatable, self.vregs);
         trace!("built vcode: {:?}", vcode);
 
         Ok(vcode)
diff --git a/cranelift/codegen/src/machinst/reg.rs b/cranelift/codegen/src/machinst/reg.rs
index 626c64e39b..a23ddcecab 100644
--- a/cranelift/codegen/src/machinst/reg.rs
+++ b/cranelift/codegen/src/machinst/reg.rs
@@ -4,7 +4,7 @@
 
 use alloc::{string::String, vec::Vec};
 use core::{fmt::Debug, hash::Hash};
-use regalloc2::{Allocation, Operand, PReg, PRegSet, VReg};
+use regalloc2::{Allocation, MachineEnv, Operand, PReg, PRegSet, VReg};
 
 #[cfg(feature = "enable-serde")]
 use serde::{Deserialize, Serialize};
@@ -38,6 +38,26 @@ pub fn first_user_vreg_index() -> usize {
     PINNED_VREGS
 }
 
+/// Collect the registers from a regalloc2 MachineEnv into a PRegSet.
+/// TODO: remove this once it's upstreamed in regalloc2
+pub fn preg_set_from_machine_env(machine_env: &MachineEnv) -> PRegSet {
+    let mut regs = PRegSet::default();
+
+    for class in machine_env.preferred_regs_by_class.iter() {
+        for reg in class.iter() {
+            regs.add(*reg);
+        }
+    }
+
+    for class in machine_env.non_preferred_regs_by_class.iter() {
+        for reg in class.iter() {
+            regs.add(*reg);
+        }
+    }
+
+    regs
+}
+
 /// A register named in an instruction. This register can be either a
 /// virtual register or a fixed physical register. It does not have
 /// any constraints applied to it: those can be added later in
@@ -289,21 +309,30 @@ pub struct OperandCollector<'a, F: Fn(VReg) -> VReg> {
     operands: &'a mut Vec<Operand>,
     operands_start: usize,
     clobbers: PRegSet,
+
+    /// The subset of physical registers that are allocatable.
+    allocatable: PRegSet,
+
     renamer: F,
 }
 
 impl<'a, F: Fn(VReg) -> VReg> OperandCollector<'a, F> {
     /// Start gathering operands into one flattened operand array.
-    pub fn new(operands: &'a mut Vec<Operand>, renamer: F) -> Self {
+    pub fn new(operands: &'a mut Vec<Operand>, allocatable: PRegSet, renamer: F) -> Self {
         let operands_start = operands.len();
         Self {
             operands,
             operands_start,
             clobbers: PRegSet::default(),
+            allocatable,
             renamer,
         }
     }
 
+    fn is_allocatable_preg(&self, reg: PReg) -> bool {
+        self.allocatable.contains(reg)
+    }
+
     /// Add an operand.
     fn add_operand(&mut self, operand: Operand) {
         let vreg = (self.renamer)(operand.vreg());
@@ -320,6 +349,12 @@ impl<'a, F: Fn(VReg) -> VReg> OperandCollector<'a, F> {
         ((start, end), self.clobbers)
     }
 
+    /// Add a use of a fixed, nonallocatable physical register.
+    pub fn reg_fixed_nonallocatable(&mut self, preg: PReg) {
+        debug_assert!(!self.is_allocatable_preg(preg));
+        self.add_operand(Operand::fixed_nonallocatable(preg))
+    }
+
     /// Add a register use, at the start of the instruction (`Before`
     /// position).
     pub fn reg_use(&mut self, reg: Reg) {
@@ -434,6 +469,19 @@ impl<'a> AllocationConsumer<'a> {
         }
     }
 
+    pub fn next_fixed_nonallocatable(&mut self, preg: PReg) {
+        let alloc = self.allocs.next();
+        let alloc = alloc.map(|alloc| {
+            Reg::from(
+                alloc
+                    .as_reg()
+                    .expect("Should not have gotten a stack allocation"),
+            )
+        });
+
+        assert_eq!(preg, alloc.unwrap().to_real_reg().unwrap().into());
+    }
+
     pub fn next(&mut self, pre_regalloc_reg: Reg) -> Reg {
         let alloc = self.allocs.next();
         let alloc = alloc.map(|alloc| {
diff --git a/cranelift/codegen/src/machinst/vcode.rs b/cranelift/codegen/src/machinst/vcode.rs
index c0423e2a26..443eab2839 100644
--- a/cranelift/codegen/src/machinst/vcode.rs
+++ b/cranelift/codegen/src/machinst/vcode.rs
@@ -541,7 +541,7 @@ impl<I: VCodeInst> VCodeBuilder<I> {
             .sort_unstable_by_key(|(vreg, _, _, _)| *vreg);
     }
 
-    fn collect_operands(&mut self) {
+    fn collect_operands(&mut self, allocatable: PRegSet) {
         for (i, insn) in self.vcode.insts.iter().enumerate() {
             // Push operands from the instruction onto the operand list.
             //
@@ -555,9 +555,10 @@ impl<I: VCodeInst> VCodeBuilder<I> {
             // its register fields (which is slow, branchy code) once.
 
             let vreg_aliases = &self.vcode.vreg_aliases;
-            let mut op_collector = OperandCollector::new(&mut self.vcode.operands, |vreg| {
-                Self::resolve_vreg_alias_impl(vreg_aliases, vreg)
-            });
+            let mut op_collector =
+                OperandCollector::new(&mut self.vcode.operands, allocatable, |vreg| {
+                    Self::resolve_vreg_alias_impl(vreg_aliases, vreg)
+                });
             insn.get_operands(&mut op_collector);
             let (ops, clobbers) = op_collector.finish();
             self.vcode.operand_ranges.push(ops);
@@ -586,14 +587,14 @@ impl<I: VCodeInst> VCodeBuilder<I> {
     }
 
     /// Build the final VCode.
-    pub fn build(mut self, vregs: VRegAllocator<I>) -> VCode<I> {
+    pub fn build(mut self, allocatable: PRegSet, vregs: VRegAllocator<I>) -> VCode<I> {
         self.vcode.vreg_types = vregs.vreg_types;
         self.vcode.reftyped_vregs = vregs.reftyped_vregs;
 
         if self.direction == VCodeBuildDirection::Backward {
             self.reverse_and_finalize();
         }
-        self.collect_operands();
+        self.collect_operands(allocatable);
 
         // Apply register aliases to the `reftyped_vregs` list since this list
         // will be returned directly to `regalloc2` eventually and all