Supported folding of constant size allocation followed by dynamic size allocation.

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index bd42896c7e062503d23d9ca0e15ab0675b923c8c..a7382edcba60bfb877d2985e1dc409efef2ef250 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -1648,25 +1648,25 @@ class HGraphBuilder {
     }
 
     HValue* EmitInternalMapCode();
-    HValue* EstablishEmptyArrayAllocationSize();
-    HValue* EstablishAllocationSize(HValue* length_node);
-    HValue* AllocateArray(HValue* size_in_bytes, HValue* capacity,
-                          HValue* length_field,
-                          FillMode fill_mode = FILL_WITH_HOLE);
 
     HGraphBuilder* builder_;
     ElementsKind kind_;
     AllocationSiteMode mode_;
     HValue* allocation_site_payload_;
     HValue* constructor_function_;
-    HInnerAllocatedObject* elements_location_;
+    HAllocate* elements_location_;
   };
 
   HValue* BuildAllocateArrayFromLength(JSArrayBuilder* array_builder,
                                        HValue* length_argument);
+  HValue* BuildCalculateElementsSize(ElementsKind kind,
+                                     HValue* capacity);
+  HConstant* EstablishHeaderAllocationSize(AllocationSiteMode mode);
+  HConstant* EstablishElementsAllocationSize(ElementsKind kind, int capacity);
 
-  HValue* BuildAllocateElements(ElementsKind kind,
-                                HValue* capacity);
+  HAllocate* BuildAllocateElements(ElementsKind kind,
+                                   HValue* size_in_bytes,
+                                   PretenureFlag pretenure);
 
   void BuildInitializeElementsHeader(HValue* elements,
                                      ElementsKind kind,
@@ -1675,16 +1675,15 @@ class HGraphBuilder {
   HValue* BuildAllocateElementsAndInitializeElementsHeader(ElementsKind kind,
                                                            HValue* capacity);
 
-  // array must have been allocated with enough room for
-  // 1) the JSArray, 2) a AllocationMemento if mode requires it,
-  // 3) a FixedArray or FixedDoubleArray.
-  // A pointer to the Fixed(Double)Array is returned.
-  HInnerAllocatedObject* BuildJSArrayHeader(HValue* array,
-                                            HValue* array_map,
-                                            AllocationSiteMode mode,
-                                            ElementsKind elements_kind,
-                                            HValue* allocation_site_payload,
-                                            HValue* length_field);
+  // Array must have been allocated with enough room for
+  // 1) the JSArray and 2) an AllocationMemento if mode requires it.
+  // Initially the array elements storage is initialized with empty array.
+  void BuildJSArrayHeader(HValue* array,
+                          HValue* array_map,
+                          AllocationSiteMode mode,
+                          ElementsKind elements_kind,
+                          HValue* allocation_site_payload,
+                          HValue* length_field);
 
   HValue* BuildGrowElementsCapacity(HValue* object,
                                     HValue* elements,