Fix bug https://code.google.com/p/dart/issues/detail?id=7994: the range analysis gives a fixed rang…

sdk/lib/_internal/compiler/implementation/ssa/value_range_analyzer.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/value_range_analyzer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/value_range_analyzer.dart	(revision 17334)
+++ sdk/lib/_internal/compiler/implementation/ssa/value_range_analyzer.dart	(working copy)
@@ -428,16 +428,17 @@
   final Value upper;
   final ValueRangeInfo info;
   Range(this.lower, this.upper, this.info);
-  Range.unbound(this.info)
-      : lower = const MinIntValue(),
-        upper = const MaxIntValue();
+
+  Range.unbound(info) : this(const MinIntValue(), const MaxIntValue(), info);
+
   /**
    * Checks if the given values are unknown, and creates a
    * range that does not have any unknown values.
    */
-  Range.normalize(Value low, Value up, this.info)
-      : lower = low == const UnknownValue() ? const MinIntValue() : low,
-        upper = up == const UnknownValue() ? const MaxIntValue() : up;
+  Range.normalize(Value low, Value up, info) : this(
+      low == const UnknownValue() ? const MinIntValue() : low,
+      up == const UnknownValue() ? const MaxIntValue() : up,
+      info);
 
   Range union(Range other) {
     return info.newNormalizedRange(
@@ -684,10 +685,10 @@
     }
 
     if (!belowLength) {
-      // Update the range of the index if using the length bounds
+      // Update the range of the index if using the maximum index
       // narrows it.
       Range newIndexRange = indexRange.intersection(
-          info.newRange(lengthRange.lower, maxIndex));
+          info.newRange(info.intZero, maxIndex));
       if (indexRange == newIndexRange) return indexRange;
       HInstruction instruction = createRangeConversion(next, check.index);
       ranges[instruction] = newIndexRange;