Use JavaScript runtime semantics when constant folding.

lib/compiler/implementation/constant_system_dart.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file

[ngeoffray, 2012/09/05 11:20:36]

Move this file to the backend?

[floitsch, 2012/09/05 16:12:01]

Left this file here. The Dart constant system is independent of the backend. It
represents the correct semantics. However, if a backend needs something else, it
should have it there.

 // 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.
 
+const DART_CONSTANT_SYSTEM = const DartConstantSystem();
+
 interface Operation {
   final SourceString name;
   bool isUserDefinable();
 }
 
 interface UnaryOperation extends Operation {
   /** Returns [:null:] if it was unable to fold the operation. */
   Constant fold(Constant constant);
 }
 
 class BitNotOperation implements UnaryOperation {
   final SourceString name = const SourceString('~');
   bool isUserDefinable() => true;
   const BitNotOperation();
   Constant fold(Constant constant) {
     if (constant.isInt()) {
       IntConstant intConstant = constant;
-      return new IntConstant(~intConstant.value);
+      return DART_CONSTANT_SYSTEM.createInt(~intConstant.value);
     }
     return null;
   }
 }
 
 class NegateOperation implements UnaryOperation {
   final SourceString name = const SourceString('negate');
   bool isUserDefinable() => true;
   const NegateOperation();
   Constant fold(Constant constant) {
     if (constant.isInt()) {
       IntConstant intConstant = constant;
-      return new IntConstant(-intConstant.value);
+      return DART_CONSTANT_SYSTEM.createInt(-intConstant.value);
     }
     if (constant.isDouble()) {
       DoubleConstant doubleConstant = constant;
-      return new DoubleConstant(-doubleConstant.value);
+      return DART_CONSTANT_SYSTEM.createDouble(-doubleConstant.value);
     }
     return null;
   }
 }
 
 class NotOperation implements UnaryOperation {
   final SourceString name = const SourceString('!');
   bool isUserDefinable() => true;
   const NotOperation();
   Constant fold(Constant constant) {
     if (constant.isBool()) {
       BoolConstant boolConstant = constant;
-      return boolConstant.negate();
+      return DART_CONSTANT_SYSTEM.createBool(!boolConstant.value);
     }
     return null;
   }
 }
 
 interface BinaryOperation extends Operation {
   /** Returns [:null:] if it was unable to fold the operation. */
   Constant fold(Constant left, Constant right);
 }
 
 /**
  * Operations that only work if both arguments are integers.
  */
-class BinaryIntOperation implements BinaryOperation {
+class BinaryBitOperation implements BinaryOperation {
   bool isUserDefinable() => true;
-  const BinaryIntOperation();
+  const BinaryBitOperation();
   Constant fold(Constant left, Constant right) {
     if (left.isInt() && right.isInt()) {
       IntConstant leftInt = left;
       IntConstant rightInt = right;
       int resultValue = foldInts(leftInt.value, rightInt.value);
       if (resultValue === null) return null;
-      return new IntConstant(resultValue);
+      return DART_CONSTANT_SYSTEM.createInt(resultValue);
     }
     return null;
   }
 
   abstract int foldInts(int left, int right);
 }
 
-class BitOrOperation extends BinaryIntOperation {
+class BitOrOperation extends BinaryBitOperation {
   final SourceString name = const SourceString('|');
   const BitOrOperation();
   int foldInts(int left, int right)  => left | right;
 }
 
-class BitAndOperation extends BinaryIntOperation {
+class BitAndOperation extends BinaryBitOperation {
   final SourceString name = const SourceString('&');
   const BitAndOperation();
   int foldInts(int left, int right) => left & right;
 }
 
-class BitXorOperation extends BinaryIntOperation {
+class BitXorOperation extends BinaryBitOperation {
   final SourceString name = const SourceString('^');
   const BitXorOperation();
   int foldInts(int left, int right) => left ^ right;
 }
 
-class ShiftLeftOperation extends BinaryIntOperation {
+class ShiftLeftOperation extends BinaryBitOperation {
   final SourceString name = const SourceString('<<');
   const ShiftLeftOperation();
   int foldInts(int left, int right) {
     // TODO(floitsch): find a better way to guard against excessive shifts to
     // the left.
     if (right > 100 || right < 0) return null;
     return left << right;
   }
 }
 
-class ShiftRightOperation extends BinaryIntOperation {
+class ShiftRightOperation extends BinaryBitOperation {
   final SourceString name = const SourceString('>>');
   const ShiftRightOperation();
   int foldInts(int left, int right) {
     if (right < 0) return null;
     return left >> right;
   }
 }
 
 class BinaryBoolOperation implements BinaryOperation {
   bool isUserDefinable() => false;
   const BinaryBoolOperation();
   Constant fold(Constant left, Constant right) {
     if (left.isBool() && right.isBool()) {
       BoolConstant leftBool = left;
       BoolConstant rightBool = right;
       bool resultValue = foldBools(leftBool.value, rightBool.value);
-      return new BoolConstant(resultValue);
+      return DART_CONSTANT_SYSTEM.createBool(resultValue);
     }
     return null;
   }
 
   abstract bool foldBools(bool left, bool right);
 }
 
-class BooleanAnd extends BinaryBoolOperation {
+class BooleanAndOperation extends BinaryBoolOperation {
   final SourceString name = const SourceString('&&');
-  const BooleanAnd();
+  const BooleanAndOperation();
   bool foldBools(bool left, bool right) => left && right;
 }
 
-class BooleanOr extends BinaryBoolOperation {
+class BooleanOrOperation extends BinaryBoolOperation {
   final SourceString name = const SourceString('||');
-  const BooleanOr();
+  const BooleanOrOperation();
   bool foldBools(bool left, bool right) => left || right;
 }
 
 class ArithmeticNumOperation implements BinaryOperation {
   bool isUserDefinable() => true;
   const ArithmeticNumOperation();
   Constant fold(Constant left, Constant right) {
     if (left.isNum() && right.isNum()) {
       NumConstant leftNum = left;
       NumConstant rightNum = right;
       num foldedValue;
       if (left.isInt() && right.isInt()) {
         foldedValue = foldInts(leftNum.value, rightNum.value);
       } else {
         foldedValue = foldNums(leftNum.value, rightNum.value);
       }
       // A division by 0 means that we might not have a folded value.
       if (foldedValue === null) return null;
       if (left.isInt() && right.isInt() && !isDivide()) {
         assert(foldedValue is int);
-        return new IntConstant(foldedValue);
+        return DART_CONSTANT_SYSTEM.createInt(foldedValue);
       } else {
-        return new DoubleConstant(foldedValue);
+        return DART_CONSTANT_SYSTEM.createDouble(foldedValue);
       }
     }
     return null;
   }
 
   bool isDivide() => false;
   num foldInts(int left, int right) => foldNums(left, right);
   abstract num foldNums(num left, num right);
 }
 
@@ skipping 37 matching lines @@
 }
 
 class AddOperation implements BinaryOperation {
   final SourceString name = const SourceString('+');
   bool isUserDefinable() => true;
   const AddOperation();
   Constant fold(Constant left, Constant right) {
     if (left.isInt() && right.isInt()) {
       IntConstant leftInt = left;
       IntConstant rightInt = right;
-      return new IntConstant(leftInt.value + rightInt.value);
+      int result = leftInt.value + rightInt.value;
+      return DART_CONSTANT_SYSTEM.createInt(result);
     } else if (left.isNum() && right.isNum()) {
       NumConstant leftNum = left;
       NumConstant rightNum = right;
-      return new DoubleConstant(leftNum.value + rightNum.value);
+      double result = leftNum.value + rightNum.value;
+      return DART_CONSTANT_SYSTEM.createDouble(result);
     } else {
       return null;
     }
   }
 }
 
 class RelationalNumOperation implements BinaryOperation {
   bool isUserDefinable() => true;
   const RelationalNumOperation();
   Constant fold(Constant left, Constant right) {
     if (left.isNum() && right.isNum()) {
       NumConstant leftNum = left;
       NumConstant rightNum = right;
       bool foldedValue = foldNums(leftNum.value, rightNum.value);
       assert(foldedValue != null);
-      return new BoolConstant(foldedValue);
+      return DART_CONSTANT_SYSTEM.createBool(foldedValue);
     }
   }
 
   abstract bool foldNums(num left, num right);
 }
 
 class LessOperation extends RelationalNumOperation {
   final SourceString name = const SourceString('<');
   const LessOperation();
   bool foldNums(num left, num right) => left < right;
@@ skipping 20 matching lines @@
 class EqualsOperation implements BinaryOperation {
   final SourceString name = const SourceString('==');
   bool isUserDefinable() => true;
   const EqualsOperation();
   Constant fold(Constant left, Constant right) {
     if (left.isNum() && right.isNum()) {
       // Numbers need to be treated specially because: NaN != NaN, -0.0 == 0.0,
       // and 1 == 1.0.
       NumConstant leftNum = left;
       NumConstant rightNum = right;
-      return new BoolConstant(leftNum.value == rightNum.value);
+      bool result = leftNum.value == rightNum.value;
+      return DART_CONSTANT_SYSTEM.createBool(result);
     }
     if (left.isConstructedObject()) {
       // Unless we know that the user-defined object does not implement the
       // equality operator we cannot fold here.
       return null;
     }
-    return new BoolConstant(left == right);
+    return DART_CONSTANT_SYSTEM.createBool(left == right);
   }
 }
 
 class IdentityOperation implements BinaryOperation {
   final SourceString name = const SourceString('===');
   bool isUserDefinable() => false;
   const IdentityOperation();
-  Constant fold(Constant left, Constant right) {
+  BoolConstant fold(Constant left, Constant right) {
     // In order to preserve runtime semantics which says that NaN !== NaN don't
     // constant fold NaN === NaN. Otherwise the output depends on inlined
     // variables and other optimizations.
     if (left.isNaN() && right.isNaN()) return null;
-    return new BoolConstant(left == right);
+    return DART_CONSTANT_SYSTEM.createBool(left == right);
   }
 }
+
+/**
+ * A [ConstantSystem] is responsible for creating constants and folding them.
+ */
+interface ConstantSystem {
+  BinaryOperation get add();
+  BinaryOperation get bitAnd();
+  UnaryOperation get bitNot();
+  BinaryOperation get bitOr();
+  BinaryOperation get bitXor();
+  BinaryOperation get booleanAnd();
+  BinaryOperation get booleanOr();
+  BinaryOperation get divide();
+  BinaryOperation get equal();
+  BinaryOperation get greaterEqual();
+  BinaryOperation get greater();
+  BinaryOperation get identity();
+  BinaryOperation get lessEqual();
+  BinaryOperation get less();
+  BinaryOperation get modulo();
+  BinaryOperation get multiply();
+  UnaryOperation get negate();
+  UnaryOperation get not();
+  BinaryOperation get shiftLeft();
+  BinaryOperation get shiftRight();
+  BinaryOperation get subtract();
+  BinaryOperation get truncatingDivide();
+
+  Constant createInt(int i);
+  Constant createDouble(double d);
+  // We need a diagnostic node to report errors in case the string is malformed.
+  Constant createString(DartString string, Node diagnosticNode);
+  Constant createBool(bool value);
+  Constant createNull();
+
+  /** Returns true if the [constant] is an integer at runtime. */
+  bool isInt(Constant constant);
+  /** Returns true if the [constant] is a double at runtime. */
+  bool isDouble(Constant constant);
+  /** Returns true if the [constant] is a string at runtime. */
+  bool isString(Constant constant);
+  /** Returns true if the [constant] is a boolean at runtime. */
+  bool isBool(Constant constant);
+  /** Returns true if the [constant] is null at runtime. */
+  bool isNull(Constant constant);
+}
+
+/**
+ * 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 implements ConstantSystem {
+  const add = const AddOperation();
+  const bitAnd = const BitAndOperation();
+  const bitNot = const BitNotOperation();
+  const bitOr = const BitOrOperation();
+  const bitXor = const BitXorOperation();
+  const booleanAnd = const BooleanAndOperation();
+  const booleanOr = const BooleanOrOperation();
+  const divide = const DivideOperation();
+  const equal = const EqualsOperation();
+  const greaterEqual = const GreaterEqualOperation();
+  const greater = const GreaterOperation();
+  const identity = const IdentityOperation();
+  const lessEqual = const LessEqualOperation();
+  const less = const LessOperation();
+  const modulo = const ModuloOperation();
+  const multiply = const MultiplyOperation();
+  const negate = const NegateOperation();
+  const not = const NotOperation();
+  const shiftLeft = const ShiftLeftOperation();
+  const shiftRight = const ShiftRightOperation();
+  const subtract = const SubtractOperation();
+  const truncatingDivide = const TruncatingDivideOperation();
+
+  const DartConstantSystem();
+
+  IntConstant createInt(int i) => new IntConstant(i);
+  DoubleConstant createDouble(double d) => new DoubleConstant(d);
+  StringConstant createString(DartString string, Node diagnosticNode)
+      => new StringConstant(string, diagnosticNode);
+  BoolConstant createBool(bool value) => new BoolConstant(value);
+  NullConstant createNull() => new NullConstant();
+
+  bool isInt(Constant constant) => constant.isInt();
+  bool isDouble(Constant constant) => constant.isDouble();
+  bool isString(Constant constant) => constant.isString();
+  bool isBool(Constant constant) => constant.isBool();
+  bool isNull(Constant constant) => constant.isNull();
+}