public void AddressOf (EmitContext ec, AddressOp Mode)
		{
			LocalTemporary value_target = new LocalTemporary (type);
				
			value_target.AddressOf (ec, AddressOp.Store);
			ec.Emit (OpCodes.Initobj, type);
			((IMemoryLocation) value_target).AddressOf (ec, Mode);
		}

		public override void Emit (EmitContext ec)
		{
			// TODO: generate less temporary variables
			LocalTemporary value_target = new LocalTemporary (type);

			value_target.AddressOf (ec, AddressOp.Store);
			ec.Emit (OpCodes.Initobj, type);
			value_target.Emit (ec);
		}

		//
		// Emits optimized equality or inequality operator when possible
		//
		void EmitEquality (EmitContext ec)
		{
			//
			// Either left or right is null
			// 
			if (UnwrapLeft != null && Binary.Right.IsNull) { // TODO: Optimize for EmitBranchable
				//
				// left.HasValue == false 
				//
				UnwrapLeft.EmitCheck (ec);
				if (Binary.Oper == Binary.Operator.Equality) {
					ec.EmitInt (0);
					ec.Emit (OpCodes.Ceq);
				}
				return;
			}

			if (UnwrapRight != null && Binary.Left.IsNull) {
				//
				// right.HasValue == false 
				//
				UnwrapRight.EmitCheck (ec);
				if (Binary.Oper == Binary.Operator.Equality) {
					ec.EmitInt (0);
					ec.Emit (OpCodes.Ceq);
				}
				return;
			}

			Label dissimilar_label = ec.DefineLabel ();
			Label end_label = ec.DefineLabel ();

			if (UserOperator != null) {
				var left = Left;

				if (UnwrapLeft != null) {
					UnwrapLeft.EmitCheck (ec);
				} else {
					// Keep evaluation order same
					if (!(Left is VariableReference)) {
						Left.Emit (ec);
						var lt = new LocalTemporary (Left.Type);
						lt.Store (ec);
						left = lt;
					}
				}

				if (UnwrapRight != null) {
					UnwrapRight.EmitCheck (ec);

					if (UnwrapLeft != null) {
						ec.Emit (OpCodes.Bne_Un, dissimilar_label);

						Label compare_label = ec.DefineLabel ();
						UnwrapLeft.EmitCheck (ec);
						ec.Emit (OpCodes.Brtrue, compare_label);

						if (Binary.Oper == Binary.Operator.Equality)
							ec.EmitInt (1);
						else
							ec.EmitInt (0);

						ec.Emit (OpCodes.Br, end_label);

						ec.MarkLabel (compare_label);
					} else {
						ec.Emit (OpCodes.Brfalse, dissimilar_label);
					}
				} else {
					ec.Emit (OpCodes.Brfalse, dissimilar_label);
				}

				var args = new Arguments (2);
				args.Add (new Argument (left));
				args.Add (new Argument (Right));

				var call = new CallEmitter ();
				call.EmitPredefined (ec, UserOperator, args);
			} else {
				if (ec.HasSet (BuilderContext.Options.AsyncBody) && Binary.Right.ContainsEmitWithAwait ()) {
					Left = Left.EmitToField (ec);
					Right = Right.EmitToField (ec);
				}

				//
				// Emit underlying value comparison first.
				//
				// For this code: int? a = 1; bool b = a == 1;
				//
				// We emit something similar to this. Expressions with side effects have local
				// variable created by Unwrap expression
				//
				//	left.GetValueOrDefault ()
				//	right
				//	bne.un.s   dissimilar_label
				//  left.HasValue
				//	br.s       end_label
//.........这里部分代码省略.........

		public void AddressOf (EmitContext ec, AddressOp mode)
		{
			IMemoryLocation ml;

			if (temp_field != null) {
				ml = temp_field as IMemoryLocation;
				if (ml == null) {
					var lt = new LocalTemporary (temp_field.Type);
					temp_field.Emit (ec);
					lt.Store (ec);
					ml = lt;
				}
			} else {
				ml = expr as VariableReference;
			}

			if (ml != null)
				ml.AddressOf (ec, mode);
			else
				LocalVariable.AddressOf (ec, mode);
		}

		protected override void EmitOperation (EmitContext ec)
		{
			Label is_null_label = ec.DefineLabel ();
			Label end_label = ec.DefineLabel ();

			LocalTemporary lt = new LocalTemporary (type);

			// Value is on the stack
			lt.Store (ec);

			var call = new CallEmitter ();
			call.InstanceExpression = lt;
			call.EmitPredefined (ec, NullableInfo.GetHasValue (expr.Type), null);

			ec.Emit (OpCodes.Brfalse, is_null_label);

			call = new CallEmitter ();
			call.InstanceExpression = lt;
			call.EmitPredefined (ec, NullableInfo.GetGetValueOrDefault (expr.Type), null);

			lt.Release (ec);

			base.EmitOperation (ec);

			ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
			ec.Emit (OpCodes.Br_S, end_label);

			ec.MarkLabel (is_null_label);
			LiftedNull.Create (type, loc).Emit (ec);

			ec.MarkLabel (end_label);
		}

		public override void Emit (EmitContext ec)
		{
			Label end_label = ec.DefineLabel ();

			if (unwrap != null) {
				Label is_null_label = ec.DefineLabel ();

				unwrap.EmitCheck (ec);
				ec.Emit (OpCodes.Brfalse, is_null_label);

				//
				// When both expressions are nullable the unwrap
				// is needed only for null check not for value uwrap
				//
				if (type.IsNullableType && TypeSpecComparer.IsEqual (NullableInfo.GetUnderlyingType (type), unwrap.Type))
					unwrap.Load (ec);
				else
					left.Emit (ec);

				ec.Emit (OpCodes.Br, end_label);

				ec.MarkLabel (is_null_label);
				right.Emit (ec);

				ec.MarkLabel (end_label);
				return;
			}

			//
			// Null check is done on original expression not after expression is converted to
			// result type. This is in most cases same but when user conversion is involved
			// we can end up in situation when user operator does the null handling which is
			// not what the operator is supposed to do.
			// There is tricky case where cast of left expression is meant to be cast of
			// whole source expression (null check is done on it) and cast from right-to-left
			// conversion needs to do null check on unconverted source expression.
			//
			if (user_conversion_left) {
				var op_expr = (UserCast) left;

				op_expr.Source.Emit (ec);
				LocalTemporary temp;

				// TODO: More load kinds can be special cased
				if (!(op_expr.Source is VariableReference)) {
					temp = new LocalTemporary (op_expr.Source.Type);
					temp.Store (ec);
					temp.Emit (ec);
					op_expr.Source = temp;
				} else {
					temp = null;
				}

				var right_label = ec.DefineLabel ();
				ec.Emit (OpCodes.Brfalse_S, right_label);
				left.Emit (ec);
				ec.Emit (OpCodes.Br, end_label);
				ec.MarkLabel (right_label);

				if (temp != null)
					temp.Release (ec);
			} else {
				//
				// Common case where expression is not modified before null check and
				// we generate better/smaller code
				//
				left.Emit (ec);
				ec.Emit (OpCodes.Dup);

				// Only to make verifier happy
				if (left.Type.IsGenericParameter)
					ec.Emit (OpCodes.Box, left.Type);

				ec.Emit (OpCodes.Brtrue, end_label);

				ec.Emit (OpCodes.Pop);
			}

			right.Emit (ec);

			ec.MarkLabel (end_label);
		}