Initial support for length guards on final fields.

runtime/vm/code_generator.cc

 // Copyright (c) 2013, 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/code_generator.h"
 
 #include "vm/assembler.h"
 #include "vm/ast.h"
 #include "vm/bigint_operations.h"
 #include "vm/code_patcher.h"
@@ skipping 1835 matching lines @@
     if (right < 0) {
       remainder -= right;
     } else {
       remainder += right;
     }
   }
   return remainder;
 }
 
 
+static intptr_t GetListLength(const Object& value) {
+  const intptr_t cid = value.GetClassId();
+  ASSERT(RawObject::IsBuiltinListClassId(cid));
+  // Extract list length.
+  if (value.IsTypedData()) {
+    const TypedData& list = TypedData::Cast(value);
+    return list.Length();
+  } else if (value.IsArray()) {
+    const Array& list = Array::Cast(value);
+    return list.Length();
+  } else if (value.IsGrowableObjectArray()) {
+    // List length is variable.
+    return Field::kNoFixedLength;
+  } else if (value.IsExternalTypedData()) {
+    // TODO(johnmccutchan): Enable for external typed data.
+    return Field::kNoFixedLength;
+  } else if (RawObject::IsTypedDataViewClassId(cid)) {
+    // TODO(johnmccutchan): Enable for typed data views.
+    return Field::kNoFixedLength;
+  }
+  UNIMPLEMENTED();
+  return Field::kNoFixedLength;
+}
+
+
 // Update global type feedback recorded for a field recording the assignment
 // of the given value.
 //   Arg0: Field object;
 //   Arg1: Value that is being stored.
 DEFINE_RUNTIME_ENTRY(UpdateFieldCid, 2) {
   ASSERT(arguments.ArgCount() == kUpdateFieldCidRuntimeEntry.argument_count());
   const Field& field = Field::CheckedHandle(arguments.ArgAt(0));
   const Object& value = Object::Handle(arguments.ArgAt(1));
-
-  field.UpdateCid(value.GetClassId());
+  const intptr_t cid = value.GetClassId();
+  field.UpdateCid(cid);
+  intptr_t list_length = Field::kNoFixedLength;
+  if ((field.guarded_cid() != kDynamicCid) &&
+      field.is_final() && RawObject::IsBuiltinListClassId(cid)) {
+    list_length = GetListLength(value);
+  }
+  field.UpdateLength(list_length);
 }
 
 }  // namespace dart