A change in the way we place TransitionElementKinds in the tree.

src/x64/lithium-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4903 matching lines @@
         }
       }
     } else {
       UNREACHABLE();
     }
   }
 }
 
 
 void LCodeGen::DoFastLiteral(LFastLiteral* instr) {
-  int size = instr->hydrogen()->total_size();
-  ElementsKind boilerplate_elements_kind =
-      instr->hydrogen()->boilerplate()->GetElementsKind();
+  Handle<JSObject> result = instr->hydrogen()->boilerplate();
 
-  // Deopt if the array literal boilerplate ElementsKind is of a type different
-  // than the expected one. The check isn't necessary if the boilerplate has
-  // already been converted to TERMINAL_FAST_ELEMENTS_KIND.
-  if (CanTransitionToMoreGeneralFastElementsKind(
-          boilerplate_elements_kind, true)) {
-    __ LoadHeapObject(rbx, instr->hydrogen()->boilerplate());
-    __ movq(rcx, FieldOperand(rbx, HeapObject::kMapOffset));
-    // Load the map's "bit field 2".
-    __ movb(rcx, FieldOperand(rcx, Map::kBitField2Offset));
-    // Retrieve elements_kind from bit field 2.
-    __ and_(rcx, Immediate(Map::kElementsKindMask));
-    __ cmpb(rcx, Immediate(boilerplate_elements_kind <<
-                           Map::kElementsKindShift));
-    DeoptimizeIf(not_equal, instr->environment());
+  if (instr->hydrogen()->TransitionRequested()) {
+    ElementsKind to_kind = instr->hydrogen()->TransitionTo();
+    result = Runtime::DeepCopyBoilerplate(isolate(),
+                                          instr->hydrogen()->boilerplate());
+    CHECK(!result.is_null());
+    // Now transition the copy
+    CHECK(!JSObject::TransitionElementsKind(result, to_kind).is_null());
+  } else {
+    ElementsKind boilerplate_elements_kind = result->GetElementsKind();
+
+    // Deopt if the array literal boilerplate ElementsKind is of a type
+    // different than the expected one. The check isn't necessary if the
+    // boilerplate has already been converted to TERMINAL_FAST_ELEMENTS_KIND.
+    if (CanTransitionToMoreGeneralFastElementsKind(
+            boilerplate_elements_kind, true)) {
+      __ LoadHeapObject(rbx, result);
+      __ movq(rcx, FieldOperand(rbx, HeapObject::kMapOffset));
+      // Load the map's "bit field 2".
+      __ movb(rcx, FieldOperand(rcx, Map::kBitField2Offset));
+      // Retrieve elements_kind from bit field 2.
+      __ and_(rcx, Immediate(Map::kElementsKindMask));
+      __ cmpb(rcx, Immediate(boilerplate_elements_kind <<
+                             Map::kElementsKindShift));
+      DeoptimizeIf(not_equal, instr->environment());
+    }
   }
 
+  // We need to compute the size now.
+  int size = 0;
+  int max_properties = HFastLiteral::kMaxLiteralProperties;
+  HFastLiteral::IsFastLiteral(result,
+                              HFastLiteral::kMaxLiteralDepth,
+                              &max_properties,
+                              &size);
+
   // Allocate all objects that are part of the literal in one big
   // allocation. This avoids multiple limit checks.
   Label allocated, runtime_allocate;
   __ AllocateInNewSpace(size, rax, rcx, rdx, &runtime_allocate, TAG_OBJECT);
   __ jmp(&allocated);
 
   __ bind(&runtime_allocate);
   __ Push(Smi::FromInt(size));
   CallRuntime(Runtime::kAllocateInNewSpace, 1, instr);
 
   __ bind(&allocated);
   int offset = 0;
-  __ LoadHeapObject(rbx, instr->hydrogen()->boilerplate());
-  EmitDeepCopy(instr->hydrogen()->boilerplate(), rax, rbx, &offset);
+  __ LoadHeapObject(rbx, result);
+  EmitDeepCopy(result, rax, rbx, &offset);
   ASSERT_EQ(size, offset);
 }
 
 
 void LCodeGen::DoObjectLiteral(LObjectLiteral* instr) {
   Handle<FixedArray> literals(instr->environment()->closure()->literals());
   Handle<FixedArray> constant_properties =
       instr->hydrogen()->constant_properties();
 
   // Set up the parameters to the stub/runtime call.
@@ skipping 456 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64