Start work on a non-complete type inferrer. Currently only analyzes return types.

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 629 matching lines @@
     // allows to easily remove the second bound check in the following
     // expression: a[1] + a[0].
     return info.newRange(info.intZero, value);
   }
 
   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];
+    assert(check.index.isInteger(types));
+    assert(check.length.isInteger(types));
 
     // 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.
     belowLength = belowLength
@@ skipping 327 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;
   }
 }