Assert that fixed allocations are to allocatable registers

cranelift/codegen/src/machinst/reg.rs

@@ -295,6 +295,26 @@ 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)
+                );
+            }
+        }
+    };
+}
+
 impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// Start gathering operands into one flattened operand array.
     pub fn new(operands: &'a mut Vec<Operand>, machine_env: &'env MachineEnv, renamer: F) -> Self {
@@ -367,13 +387,15 @@ impl<'a, 'env, F: Fn(VReg) -> VReg> OperandCollector<'a, 'env, F> {
     /// 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);
         let rreg = rreg.to_real_reg().expect("fixed reg is not a RealReg");
         self.add_operand(Operand::reg_fixed_use(reg.into(), rreg.into()));
     }
 
     /// 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);
         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()));
     }