Port and integrate the irregexp engine from V8

runtime/vm/flow_graph_range_analysis.cc

Index: runtime/vm/flow_graph_range_analysis.cc
diff --git a/runtime/vm/flow_graph_range_analysis.cc b/runtime/vm/flow_graph_range_analysis.cc
index ed335dab73c5c99d3f5d62f2eb6dc8ea2aab8bdf..61d45289e34b7f74121f5ce3349f95744ebf6dd4 100644
--- a/runtime/vm/flow_graph_range_analysis.cc
+++ b/runtime/vm/flow_graph_range_analysis.cc
@@ -2826,6 +2826,22 @@ void LoadIndexedInstr::InferRange(RangeAnalysis* analysis, Range* range) {
 }
 
 
+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_);