Add Opnd::None error message to x86 backend as well

yjit/src/backend/arm64/mod.rs

@@ -50,8 +50,11 @@ impl From<Opnd> for A64Opnd {
                 panic!("attempted to lower an Opnd::Mem with a MemBase::InsnOut base")
             },
             Opnd::InsnOut { .. } => panic!("attempted to lower an Opnd::InsnOut"),
-            Opnd::None => panic!("attempted to lower an Opnd::None"),
             Opnd::Value(_) => panic!("attempted to lower an Opnd::Value"),
+            Opnd::None => panic!(
+                "Attempted to lower an Opnd::None. This often happens when an out operand was not allocated for an instruction because the output of the instruction was not used. Please ensure you are using the output."
+            ),
+
         }
     }
 }

yjit/src/backend/x86_64/mod.rs

@@ -40,8 +40,6 @@ impl From<Opnd> for X86Opnd {
 
             Opnd::InsnOut{..} => panic!("InsnOut operand made it past register allocation"),
 
-            Opnd::None => X86Opnd::None,
-
             Opnd::UImm(val) => uimm_opnd(val),
             Opnd::Imm(val) => imm_opnd(val),
             Opnd::Value(VALUE(uimm)) => uimm_opnd(uimm as u64),
@@ -60,6 +58,10 @@ impl From<Opnd> for X86Opnd {
                 mem_opnd(num_bits, X86Opnd::Reg(reg), disp)
             }
 
+            Opnd::None => panic!(
+                "Attempted to lower an Opnd::None. This often happens when an out operand was not allocated for an instruction because the output of the instruction was not used. Please ensure you are using the output."
+            ),
+
             _ => panic!("unsupported x86 operand type")
         }
     }