Make value range analysis tolerate erroneous length expressions.

pkg/compiler/lib/src/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 693 matching lines @@
 
   Range visitBoundsCheck(HBoundsCheck check) {
     // Save the next instruction, in case the check gets removed.
     HInstruction next = check.next;
     Range indexRange = ranges[check.index];
     Range lengthRange = ranges[check.length];
     if (indexRange == null) {
       indexRange = info.newUnboundRange();
       assert(!check.index.isInteger(compiler));
     }
+    if (lengthRange == null) {
+      // We might have lost the length range due to a type conversion that
+      // asserts a non-integer type. In such a case, the program will never
+      // get to this point anyway, so no need to try and refine ranges.
+      return indexRange;
+    }
     assert(check.length.isInteger(compiler));
 
     // Check if the index is strictly below the upper bound of the length
     // range.
     Value maxIndex = lengthRange.upper - info.intOne;
     bool belowLength = maxIndex != const MaxIntValue()
         && indexRange.upper.min(maxIndex) == indexRange.upper;
 
     // Check if the index is strictly below the lower bound of the length
     // range.
@@ skipping 345 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);
   }
 }