Cache IC handlers on the prototype's map if possible

src/x64/stub-cache-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/arguments.h"
 #include "src/codegen.h"
@@ skipping 757 matching lines @@
              NameDictionary::kNotFound);
 
       GenerateDictionaryNegativeLookup(masm(), miss, reg, name,
                                        scratch1, scratch2);
 
       __ movp(scratch1, FieldOperand(reg, HeapObject::kMapOffset));
       reg = holder_reg;  // From now on the object will be in holder_reg.
       __ movp(reg, FieldOperand(scratch1, Map::kPrototypeOffset));
     } else {
       bool in_new_space = heap()->InNewSpace(*prototype);
-      if (in_new_space) {
+      // Two possible reasons for loading the prototype from the map:
+      // (1) Can't store references to new space in code.
+      // (2) Handler is shared for all receivers with the same prototype
+      //     map (but not necessarily the same prototype instance).
+      bool load_prototype_from_map = in_new_space || depth == 1;
+      if (load_prototype_from_map) {
         // Save the map in scratch1 for later.
         __ movp(scratch1, FieldOperand(reg, HeapObject::kMapOffset));
       }
       if (depth != 1 || check == CHECK_ALL_MAPS) {
         __ CheckMap(reg, current_map, miss, DONT_DO_SMI_CHECK);
       }
 
       // Check access rights to the global object.  This has to happen after
       // the map check so that we know that the object is actually a global
       // object.
       if (current_map->IsJSGlobalProxyMap()) {
         __ CheckAccessGlobalProxy(reg, scratch2, miss);
       } else if (current_map->IsJSGlobalObjectMap()) {
         GenerateCheckPropertyCell(
             masm(), Handle<JSGlobalObject>::cast(current), name,
             scratch2, miss);
       }
       reg = holder_reg;  // From now on the object will be in holder_reg.
 
-      if (in_new_space) {
-        // The prototype is in new space; we cannot store a reference to it
-        // in the code.  Load it from the map.
+      if (load_prototype_from_map) {
         __ movp(reg, FieldOperand(scratch1, Map::kPrototypeOffset));
       } else {
-        // The prototype is in old space; load it directly.
         __ Move(reg, prototype);
       }
     }
 
     // Go to the next object in the prototype chain.
     current = prototype;
     current_map = handle(current->map());
   }
 
   // Log the check depth.
@@ skipping 627 matching lines @@
   // -----------------------------------
   TailCallBuiltin(masm, Builtins::kKeyedLoadIC_Miss);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64