Port and integrate the irregexp engine from V8

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index 894d0f9047c3d2f44ec07336788ce1ed2218111a..b35f91e901b97be7be17233ba0df8f01e8a347ba 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -227,7 +227,8 @@ bool FlowGraphCompiler::ForceSlowPathForStackOverflow() const {
 static bool IsEmptyBlock(BlockEntryInstr* block) {
   return !block->HasParallelMove() &&
          block->next()->IsGoto() &&
-         !block->next()->AsGoto()->HasParallelMove();
+         !block->next()->AsGoto()->HasParallelMove() &&
+         !block->IsIndirectEntry();
 }
 
 
@@ -354,6 +355,7 @@ void FlowGraphCompiler::VisitBlocks() {
 
     LoopInfoComment(assembler(), *entry, *loop_headers);
 
+    entry->set_offset(assembler()->CodeSize());
     entry->EmitNativeCode(this);
     // Compile all successors until an exit, branch, or a block entry.
     for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
@@ -817,6 +819,9 @@ void FlowGraphCompiler::FinalizeStackmaps(const Code& code) {
 
 
 void FlowGraphCompiler::FinalizeVarDescriptors(const Code& code) {
+  // Irregexp functions do not have a node sequence.
+  if (flow_graph().IsIrregexpFunction()) return;
+
   const LocalVarDescriptors& var_descs = LocalVarDescriptors::Handle(
           parsed_function_.node_sequence()->scope()->GetVarDescriptors(
               parsed_function_.function()));