Port and integrate the irregexp engine from V8

runtime/vm/flow_graph_range_analysis.cc

 // Copyright (c) 2014, 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.
 
 #include "vm/flow_graph_range_analysis.h"
 
 #include "vm/bit_vector.h"
 #include "vm/il_printer.h"
 
 namespace dart {
@@ skipping 2808 matching lines @@
       *range = Range(RangeBoundary::FromConstant(0),
                      RangeBoundary::FromConstant(0xFFFF));
       break;
     default:
       Definition::InferRange(analysis, range);
       break;
   }
 }
 
 
+void LoadCodeUnitsInstr::InferRange(RangeAnalysis* analysis, Range* range) {
+  ASSERT(class_id() == kOneByteStringCid ||
+         class_id() == kTwoByteStringCid);
+  switch (class_id()) {
+    case kOneByteStringCid:
+    case kTwoByteStringCid:
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(kMaxUint32));
+      break;
+    default:
+      UNREACHABLE();
+      break;
+  }
+}
+
+
 void IfThenElseInstr::InferRange(RangeAnalysis* analysis, Range* range) {
   const intptr_t min = Utils::Minimum(if_true_, if_false_);
   const intptr_t max = Utils::Maximum(if_true_, if_false_);
   *range = Range(RangeBoundary::FromConstant(min),
                  RangeBoundary::FromConstant(max));
 }
 
 
 static RangeBoundary::RangeSize RepresentationToRangeSize(Representation r) {
   switch (r) {
@@ skipping 200 matching lines @@
     }
   } while (CanonicalizeMaxBoundary(&max) ||
            CanonicalizeMinBoundary(&canonical_length));
 
   // Failed to prove that maximum is bounded with array length.
   return false;
 }
 
 
 }  // namespace dart