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

src/hydrogen.h

 // 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 1648 matching lines @@
     JSArrayBuilder(HGraphBuilder* builder,
                    ElementsKind kind,
                    HValue* constructor_function = NULL);
 
     enum FillMode {
       DONT_FILL_WITH_HOLE,
       FILL_WITH_HOLE
     };
 
     ElementsKind kind() { return kind_; }
+    HAllocate* elements_location() { return elements_location_; }
 
-    HValue* AllocateEmptyArray();
-    HValue* AllocateArray(HValue* capacity, HValue* length_field,
-                          FillMode fill_mode = FILL_WITH_HOLE);
+    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();
 
    private:
     Zone* zone() const { return builder_->zone(); }
     int elements_size() const {
       return IsFastDoubleElementsKind(kind_) ? kDoubleSize : kPointerSize;
     }
     HGraphBuilder* builder() { return builder_; }
     HGraph* graph() { return builder_->graph(); }
     int initial_capacity() {
       STATIC_ASSERT(JSArray::kPreallocatedArrayElements > 0);
       return JSArray::kPreallocatedArrayElements;
     }
 
     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,
                                      HValue* capacity);
 
   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,
                                     ElementsKind kind,
                                     ElementsKind new_kind,
                                     HValue* length,
                                     HValue* new_capacity);
 
   void BuildFillElementsWithHole(HValue* elements,
                                  ElementsKind elements_kind,
@@ skipping 960 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_