dart2js cps: Introduce some built-in operators in type propagation.

pkg/compiler/lib/src/cps_ir/builtin_operator.dart

+// Copyright (c) 2015, 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 builtin_operator;
+// This is shared by the CPS and Tree IRs.
+// Both cps_ir_nodes and tree_ir_nodes import and re-export this file.
+
+/// An operator supported natively in the CPS and Tree IRs using the
+/// `ApplyBuiltinOperator` instructions.
+///
+/// These operators are pure in the sense that they cannot throw, diverge,
+/// have observable side-effects, return new objects, nor depend on any
+/// mutable state.
+///
+/// Most operators place restrictions on the values that may be given as
+/// argument; their behaviour is unspecified if those requirements are violated.
+///
+/// In all cases, the word "null" refers to the Dart null object, corresponding
+/// to both JS null and JS undefined.
+enum BuiltinOperator {
+  /// The numeric binary operators must take two numbers as argument.
+  /// The bitwise operators coerce the result to an unsigned integer, but
+  /// otherwise these all behave like the corresponding JS operator.
+  NumAdd,
+  NumSubtract,
+  NumMultiply,
+  NumAnd,
+  NumOr,
+  NumXor,
+  NumLt,
+  NumLe,
+  NumGt,
+  NumGe,
+
+  /// Returns true if the two arguments are the same value, and that value is
+  /// not NaN, or if one argument is +0 and the other is -0.
+  ///
+  /// At most one of the arguments may be null.
+  StrictEq,
+
+  /// Negated version of [StrictEq]. Introduced by [LogicalRewriter] in Tree IR.
+  StrictNeq,
+
+  /// Returns true if the two arguments are both null or are the same string,
+  /// boolean, or number, and that number is not NaN, or one argument is +0
+  /// and the other is -0.
+  ///
+  /// One of the following must hold:
+  /// - At least one argument is null.
+  /// - Arguments are both strings, or both booleans, or both numbers.
+  LooseEq,
+
+  /// Negated version of [LooseEq]. Introduced by [LogicalRewriter] in Tree IR.
+  LooseNeq,
+
+  /// Returns true if the argument is false, +0. -0, NaN, the empty string,
+  /// or null.
+  IsFalsy
+}