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 643074c3df878fe431d224f551c9202fa9461eb3..272b1eb02eea292cc1de5693238a2adfc3dc20ff 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -1666,10 +1666,24 @@ class HGraphBuilder {
     };
 
     ElementsKind kind() { return kind_; }
-
-    HValue* AllocateEmptyArray();
-    HValue* AllocateArray(HValue* capacity, HValue* length_field,
-                          FillMode fill_mode = FILL_WITH_HOLE);
+    HAllocate* elements_location() { return elements_location_; }
+
+    HAllocate* AllocateEmptyArray();
+    HAllocate* AllocateArray(HValue* capacity,
+                             HValue* length_field,
+                             FillMode fill_mode = FILL_WITH_HOLE);
+    // Use these allocators when capacity could be unknown at compile time
+    // but its limit is known. For constant |capacity| the value of
+    // |capacity_upper_bound| is ignored and the actual |capacity|
+    // value is used as an upper bound.
+    HAllocate* AllocateArray(HValue* capacity,
+                             int capacity_upper_bound,
+                             HValue* length_field,
+                             FillMode fill_mode = FILL_WITH_HOLE);
+    HAllocate* AllocateArray(HValue* capacity,
+                             HConstant* capacity_upper_bound,
+                             HValue* length_field,
+                             FillMode fill_mode = FILL_WITH_HOLE);
     HValue* GetElementsLocation() { return elements_location_; }
     HValue* EmitMapCode();
 
@@ -1686,25 +1700,25 @@ 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,
@@ -1713,16 +1727,15 @@ 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,