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

 // 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.
 
 part of ssa;
 
 
 class ValueRangeInfo {
   final ConstantSystem constantSystem;
 
@@ skipping 410 matching lines @@
 /**
  * A [Range] represents the possible integer values an instruction
  * can have, from its [lower] bound to its [upper] bound, both
  * included.
  */
 class Range {
   final Value lower;
   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(
         lower.min(other.lower), upper.max(other.upper));
   }
 
   intersection(Range other) {
     Value low = lower.max(other.lower);
     Value up = upper.min(other.upper);
     // If we could not compute max or min, pick a value in the two
@@ skipping 226 matching lines @@
       // greater or equal than the lower bound of the index.
       Value low = lengthRange.lower.max(indexRange.lower);
       if (low != const UnknownValue()) {
         HInstruction instruction =
             createRangeConversion(next, check.length);
         ranges[instruction] = info.newRange(low, lengthRange.upper);
       }
     }
 
     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;
       return newIndexRange;
     }
 
     return indexRange;
   }
 
   Range visitRelational(HRelational relational) {
@@ skipping 286 matching lines @@
     if (instruction is HPhi && !instruction.block.isLoopHeader()) {
       HInstruction result = unwrap(instruction.inputs[0]);
       for (int i = 1; i < instruction.inputs.length; i++) {
         if (result != unwrap(instruction.inputs[i])) return instruction;
       }
       return result;
     }
     return instruction;
   }
 }