Revert "dart2js: Constant fold num.round()"

pkg/compiler/lib/src/constant_system_dart.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.constant_system.dart;
 
 import 'compiler.dart' show Compiler;
 import 'constants/constant_system.dart';
 import 'constants/values.dart';
 import 'dart_types.dart';
@@ skipping 330 matching lines @@
   final String name = '??';
   const IfNullOperation();
   ConstantValue fold(ConstantValue left, ConstantValue right) {
     if (left.isNull) return right;
     return left;
   }
 
   apply(left, right) => left ?? right;
 }
 
-class CodeUnitAtOperation implements BinaryOperation {
-  String get name => 'charCodeAt';
+abstract class CodeUnitAtOperation implements BinaryOperation {
+  final String name = 'charCodeAt';
   const CodeUnitAtOperation();
-  ConstantValue fold(ConstantValue left, ConstantValue right) => null;
   apply(left, right) => left.codeUnitAt(right);
 }
 
+class CodeUnitAtConstantOperation extends CodeUnitAtOperation {
+  const CodeUnitAtConstantOperation();
+  ConstantValue fold(ConstantValue left, ConstantValue right) {
+    // 'a'.codeUnitAt(0) is not a constant expression.
+    return null;
+  }
+}
+
 class CodeUnitAtRuntimeOperation extends CodeUnitAtOperation {
   const CodeUnitAtRuntimeOperation();
   IntConstantValue fold(ConstantValue left, ConstantValue right) {
     if (left.isString && right.isInt) {
       StringConstantValue stringConstant = left;
       IntConstantValue indexConstant = right;
       DartString dartString = stringConstant.primitiveValue;
       int index = indexConstant.primitiveValue;
       if (index < 0 || index >= dartString.length) return null;
       String string = dartString.slowToString();
       int value = string.codeUnitAt(index);
       return DART_CONSTANT_SYSTEM.createInt(value);
     }
     return null;
   }
 }
 
-class UnfoldedUnaryOperation implements UnaryOperation {
-  final String name;
-  const UnfoldedUnaryOperation(this.name);
-  ConstantValue fold(ConstantValue constant) {
-    return null;
-  }
-}
-
 /**
  * A constant system implementing the Dart semantics. This system relies on
  * the underlying runtime-system. That is, if dart2js is run in an environment
  * that doesn't correctly implement Dart's semantics this constant system will
  * not return the correct values.
  */
 class DartConstantSystem extends ConstantSystem {
   final add = const AddOperation();
   final bitAnd = const BitAndOperation();
   final bitNot = const BitNotOperation();
@@ skipping 10 matching lines @@
   final lessEqual = const LessEqualOperation();
   final less = const LessOperation();
   final modulo = const ModuloOperation();
   final multiply = const MultiplyOperation();
   final negate = const NegateOperation();
   final not = const NotOperation();
   final shiftLeft = const ShiftLeftOperation();
   final shiftRight = const ShiftRightOperation();
   final subtract = const SubtractOperation();
   final truncatingDivide = const TruncatingDivideOperation();
-  final codeUnitAt = const CodeUnitAtOperation();
-  final round = const UnfoldedUnaryOperation('round');
+  final codeUnitAt = const CodeUnitAtConstantOperation();
 
   const DartConstantSystem();
 
   @override
   IntConstantValue createInt(int i) => new IntConstantValue(i);
 
   @override
   DoubleConstantValue createDouble(double d) => new DoubleConstantValue(d);
 
   @override
@@ skipping 37 matching lines @@
   bool isInt(ConstantValue constant) => constant.isInt;
   bool isDouble(ConstantValue constant) => constant.isDouble;
   bool isString(ConstantValue constant) => constant.isString;
   bool isBool(ConstantValue constant) => constant.isBool;
   bool isNull(ConstantValue constant) => constant.isNull;
 
   bool isSubtype(DartTypes types, DartType s, DartType t) {
     return types.isSubtype(s, t);
   }
 }