Fix bug in our SSA optimizations: by giving an empty type to a box, we were assuming that anything …

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 662 matching lines @@
     IntConstant constantInt = constant.constant;
     Value value = info.newIntValue(constantInt.value);
     return info.newNormalizedRange(value, value);
   }
 
   Range visitFieldGet(HFieldGet fieldGet) {
     if (!fieldGet.isInteger(compiler)) return info.newUnboundRange();
     if (!fieldGet.receiver.isIndexable(compiler)) {
       return visitInstruction(fieldGet);
     }
+    JavaScriptBackend backend = compiler.backend;
+    assert(fieldGet.element == backend.jsIndexableLength);
     LengthValue value = info.newLengthValue(fieldGet);
     // We know this range is above zero. To simplify the analysis, we
     // put the zero value as the lower bound of this range. This
     // allows to easily remove the second bound check in the following
     // expression: a[1] + a[0].
     return info.newNormalizedRange(info.intZero, value);
   }
 
   Range visitBoundsCheck(HBoundsCheck check) {
     // Save the next instruction, in case the check gets removed.
@@ skipping 313 matching lines @@
   }
 
   Range handleBinaryOperation(HBinaryArithmetic instruction) {
     Range leftRange = visit(instruction.left);
     Range rightRange = visit(instruction.right);
     if (leftRange == null || rightRange == null) return null;
     BinaryOperation operation = instruction.operation(info.constantSystem);
     return operation.apply(leftRange, rightRange);
   }
 }