Special case -0.0 when constant folding.

dart/frog/leg/ssa/nodes.dart

 // Copyright (c) 2011, 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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
@@ skipping 104 matching lines @@
   HBasicBlock entry;
   HBasicBlock exit;
   final List<HBasicBlock> blocks;
 
   // We canonicalize all literals used within a graph so we do not
   // have to worry about them for global value numbering.
   HLiteral nullLiteral;
   HLiteral trueLiteral;
   HLiteral falseLiteral;
   HLiteral nanLiteral;
+  HLiteral negativeZeroLiteral;
   Map<int, HLiteral> intLiterals;
   Map<double, HLiteral> doubleLiterals;
   Map<num, HLiteral> numLiterals;
   Map<String, HLiteral> stringLiterals;
 
   HGraph() : blocks = new List<HBasicBlock>() {
     entry = addNewBlock();
     // The exit block will be added later, so it has an id that is
     // after all others in the system.
     exit = new HBasicBlock();
@@ skipping 30 matching lines @@
   }
 
   HLiteral addNewLiteralNaN() {
     if (nanLiteral === null) {
       nanLiteral = new HLiteral.internal(double.NAN, HType.DOUBLE);
       entry.addAtExit(nanLiteral);
     }
     return nanLiteral;
   }
 
+  HLiteral addNewNegativeZeroLiteral() {
+    if (negativeZeroLiteral === null) {
+      negativeZeroLiteral = new HLiteral.internal(-0.0, HType.DOUBLE);
+      entry.addAtExit(negativeZeroLiteral);
+    }
+    return negativeZeroLiteral;
+  }
+
   HLiteral addNewLiteralDouble(double value) {
     if (value.isNaN()) return addNewLiteralNaN();  // Avoid hashing NaN.
+    if (value == 0 && value.isNegative()) {
+      // Avoid hashing -0.0 as it compares equal to 0.0.
+      return addNewNegativeZeroLiteral();
+    }
     if (doubleLiterals === null) doubleLiterals = new Map<double, HLiteral>();
     HLiteral result = doubleLiterals[value];
     if (result === null) {
       result = new HLiteral.internal(value, HType.DOUBLE);
       entry.addAtExit(result);
       doubleLiterals[value] = result;
     }
     return result;
   }
 
@@ skipping 2066 matching lines @@
 
   HInstruction get expression() => inputs[0];
 
   HType computeType() => HType.BOOLEAN;
   bool hasExpectedType() => true;
 
   accept(HVisitor visitor) => visitor.visitIs(this);
 
   toString() => "$expression is $typeExpression";
 }