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

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index c69b27c445568e21b07d7ee2d638d8cce38702a0..1ffea9851ee31dc4c3367531dcd6a40e31da9b97 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -4921,26 +4921,43 @@ void LCodeGen::EmitDeepCopy(Handle<JSObject> object,
 
 
 void LCodeGen::DoFastLiteral(LFastLiteral* instr) {
-  int size = instr->hydrogen()->total_size();
-  ElementsKind boilerplate_elements_kind =
-      instr->hydrogen()->boilerplate()->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, 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());
+  Handle<JSObject> result = instr->hydrogen()->boilerplate();
+
+  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;
@@ -4953,8 +4970,8 @@ void LCodeGen::DoFastLiteral(LFastLiteral* 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);
 }