public override void Emit (EmitContext ec)
		{
			if (IsBitwiseBoolean && UserOperator == null) {
				EmitBitwiseBoolean (ec);
				return;
			}

			if ((Binary.Oper & Binary.Operator.EqualityMask) != 0) {
				EmitEquality (ec);
				return;
			}

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

			if (ec.HasSet (BuilderContext.Options.AsyncBody) && Right.ContainsEmitWithAwait ()) {
				Left = Left.EmitToField (ec);
				Right = Right.EmitToField (ec);
			}

			if (UnwrapLeft != null) {
				UnwrapLeft.EmitCheck (ec);
			}

			//
			// Don't emit HasValue check when left and right expressions are same
			//
			if (UnwrapRight != null && !Binary.Left.Equals (Binary.Right)) {
				UnwrapRight.EmitCheck (ec);
				if (UnwrapLeft != null) {
					ec.Emit (OpCodes.And);
				}
			}

			ec.Emit (OpCodes.Brfalse, is_null_label);

			if (UserOperator != null) {
				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 {
				Binary.EmitOperator (ec, Left, Right);
			}

			//
			// Wrap the result when the operator return type is nullable type
			//
			if (type.IsNullableType)
				ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));

			ec.Emit (OpCodes.Br_S, end_label);
			ec.MarkLabel (is_null_label);

			if ((Binary.Oper & Binary.Operator.ComparisonMask) != 0) {
				ec.EmitInt (0);
			} else {
				LiftedNull.Create (type, loc).Emit (ec);
			}

			ec.MarkLabel (end_label);
		}

		//
		// 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 EmitCheck (EmitContext ec)
		{
			Store (ec);

			var call = new CallEmitter ();
			call.InstanceExpression = this;

			call.EmitPredefined (ec, NullableInfo.GetHasValue (expr.Type), null);
		}

		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)
		{
			Store (ec);

			var call = new CallEmitter ();
			call.InstanceExpression = this;

			if (useDefaultValue)
				call.EmitPredefined (ec, NullableInfo.GetGetValueOrDefault (expr.Type), null);
			else
				call.EmitPredefined (ec, NullableInfo.GetValue (expr.Type), null);
		}