Improve compilation speed on a pathological case > 2x (7 sec -> 2.7 sec) by improving local lookups.

runtime/vm/object.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 3882 matching lines @@
     const String& str_;
     int32_t ch_;
     intptr_t index_;
     intptr_t end_;
     DISALLOW_IMPLICIT_CONSTRUCTORS(CodePointIterator);
   };
 
   intptr_t Length() const { return Smi::Value(raw_ptr()->length_); }
   static intptr_t length_offset() { return OFFSET_OF(RawString, length_); }
 
-  virtual intptr_t Hash() const;
+  virtual intptr_t Hash() const {

[Ivan Posva, 2013/01/15 06:05:15]

Can you explain to me why Hash() is a virtual in the String class? I do not see
this overriding a virtual Hash in a base class, nor are there subclasses of
String that override Hash.

[srdjan, 2013/01/15 18:58:28]

Apparently, the reason is historical. There is no need  for it being virtual.
Removed StringHash.

+    return StringHash();
+  }
+
+  // Non-virtual, higher performance when type is known.
+  intptr_t StringHash() const {
+    intptr_t result = Smi::Value(raw_ptr()->hash_);
+    if (result != 0) {
+      return result;
+    }
+    result = String::Hash(*this, 0, this->Length());
+    this->SetHash(result);
+    return result;
+  }
+
   static intptr_t hash_offset() { return OFFSET_OF(RawString, hash_); }
   static intptr_t Hash(const String& str, intptr_t begin_index, intptr_t len);
   static intptr_t Hash(const uint8_t* characters, intptr_t len);
   static intptr_t Hash(const uint16_t* characters, intptr_t len);
   static intptr_t Hash(const int32_t* characters, intptr_t len);
 
   int32_t CharAt(intptr_t index) const;
 
   intptr_t CharSize() const;
 
@@ skipping 2339 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_