VM: Optimize RegExp.matchAsPrefix(...) by generating a sticky RegExp specialization.

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
diff --git a/runtime/vm/raw_object_snapshot.cc b/runtime/vm/raw_object_snapshot.cc
index aebda455c32d238e3cc9740d2de013af9e600db3..cc90d0b812e24b70c8a775c15a2f48ef67813ed4 100644
--- a/runtime/vm/raw_object_snapshot.cc
+++ b/runtime/vm/raw_object_snapshot.cc
@@ -2896,14 +2896,11 @@ RawRegExp* RegExp::ReadFrom(SnapshotReader* reader,
 
   // TODO(18854): Need to implement a way of recreating the irrexp functions.

[rmacnak, 2016/11/17 00:49:52]

Remove this todo.

[Vyacheslav Egorov (Google), 2016/11/17 16:51:33]

Done.

   const Function& no_function = Function::Handle(reader->zone());
-  regex.set_function(kOneByteStringCid, no_function);
-  regex.set_function(kTwoByteStringCid, no_function);
-  regex.set_function(kExternalOneByteStringCid, no_function);
-  regex.set_function(kExternalTwoByteStringCid, no_function);
-
-  const TypedData& no_bytecode = TypedData::Handle(reader->zone());
-  regex.set_bytecode(true, no_bytecode);
-  regex.set_bytecode(false, no_bytecode);
+  for (intptr_t cid = kOneByteStringCid; cid <= kExternalTwoByteStringCid;

[erikcorry, 2016/11/17 13:56:17]

Here and elsewhere you put in a loop. Perhaps there should be kFirstStringCid
and kLastStringCid for use in loops, which are equal in value to the current
kOneByteStringCid and kExternalTwoByteStringCid.

[Vyacheslav Egorov (Google), 2016/11/17 16:51:33]

Yeah, that sounds like a nice improvement - but I will not do that as a part of
this CL.

+       cid++) {
+    regex.set_function(cid, /*sticky=*/false, no_function);
+    regex.set_function(cid, /*sticky=*/true, no_function);
+  }
 
   return regex.raw();
 }