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

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index f7b310003e0c1140936a8c86d51638534acd824a..ac0a4b0c862e08622d5d8b604b57ce5580132d30 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -2136,7 +2136,6 @@ HInstruction* HGraphBuilder::BuildUncheckedMonomorphicElementAccess(
 }
 
 
-
 HValue* HGraphBuilder::BuildAllocateArrayFromLength(
     JSArrayBuilder* array_builder,
     HValue* length_argument) {
@@ -2179,29 +2178,36 @@ HValue* HGraphBuilder::BuildAllocateArrayFromLength(
   return array_builder->AllocateArray(capacity, length);
 }
 
-HValue* HGraphBuilder::BuildAllocateElements(ElementsKind kind,
-                                             HValue* capacity) {
-  int elements_size;
-  InstanceType instance_type;
-
-  if (IsFastDoubleElementsKind(kind)) {
-    elements_size = kDoubleSize;
-    instance_type = FIXED_DOUBLE_ARRAY_TYPE;
-  } else {
-    elements_size = kPointerSize;
-    instance_type = FIXED_ARRAY_TYPE;
-  }
+HValue* HGraphBuilder::BuildCalculateElementsSize(ElementsKind kind,
+                                                  HValue* capacity) {
+  int elements_size = IsFastDoubleElementsKind(kind)
+      ? kDoubleSize
+      : kPointerSize;
 
   HConstant* elements_size_value = Add<HConstant>(elements_size);
-  HValue* mul = AddUncasted<HMul>(capacity, elements_size_value);
+  HInstruction* mul = HMul::NewImul(zone(), context(),
+                                    capacity->ActualValue(),
+                                    elements_size_value);
+  AddInstruction(mul);
   mul->ClearFlag(HValue::kCanOverflow);
 
+  STATIC_ASSERT(FixedDoubleArray::kHeaderSize == FixedArray::kHeaderSize);
+
   HConstant* header_size = Add<HConstant>(FixedArray::kHeaderSize);
   HValue* total_size = AddUncasted<HAdd>(mul, header_size);
   total_size->ClearFlag(HValue::kCanOverflow);
+  return total_size;
+}
 
-  return Add<HAllocate>(total_size, HType::JSArray(),
-      isolate()->heap()->GetPretenureMode(), instance_type);
+HValue* HGraphBuilder::BuildAllocateElements(ElementsKind kind,
+                                             HValue* size_in_bytes,
+                                             PretenureFlag pretenure) {
+  InstanceType instance_type = IsFastDoubleElementsKind(kind)
+      ? FIXED_DOUBLE_ARRAY_TYPE
+      : FIXED_ARRAY_TYPE;
+
+  return Add<HAllocate>(size_in_bytes, HType::JSArray(),
+                        pretenure, instance_type);
 }
 
 
@@ -2225,43 +2231,39 @@ HValue* HGraphBuilder::BuildAllocateElementsAndInitializeElementsHeader(
   // The HForceRepresentation is to prevent possible deopt on int-smi
   // conversion after allocation but before the new object fields are set.
   capacity = AddUncasted<HForceRepresentation>(capacity, Representation::Smi());
-  HValue* new_elements = BuildAllocateElements(kind, capacity);
+  HValue* size_in_bytes = BuildCalculateElementsSize(kind, capacity);
+  HValue* new_elements = BuildAllocateElements(
+      kind, size_in_bytes, isolate()->heap()->GetPretenureMode());
   BuildInitializeElementsHeader(new_elements, kind, capacity);
   return new_elements;
 }
 
 
-HInnerAllocatedObject* HGraphBuilder::BuildJSArrayHeader(HValue* array,
-    HValue* array_map,
-    AllocationSiteMode mode,
-    ElementsKind elements_kind,
-    HValue* allocation_site_payload,
-    HValue* length_field) {
-
+void HGraphBuilder::BuildJSArrayHeader(HValue* array,
+                                       HValue* array_map,
+                                       AllocationSiteMode mode,
+                                       ElementsKind elements_kind,
+                                       HValue* allocation_site_payload,
+                                       HValue* length_field) {
   Add<HStoreNamedField>(array, HObjectAccess::ForMap(), array_map);
 
   HConstant* empty_fixed_array =
     Add<HConstant>(isolate()->factory()->empty_fixed_array());
 
-  HObjectAccess access = HObjectAccess::ForPropertiesPointer();
-  Add<HStoreNamedField>(array, access, empty_fixed_array);
-  Add<HStoreNamedField>(array, HObjectAccess::ForArrayLength(elements_kind),
-                        length_field);
+  Add<HStoreNamedField>(
+      array, HObjectAccess::ForPropertiesPointer(), empty_fixed_array);
+
+  Add<HStoreNamedField>(
+      array, HObjectAccess::ForElementsPointer(), empty_fixed_array);
+
+  Add<HStoreNamedField>(
+      array, HObjectAccess::ForArrayLength(elements_kind), length_field);
 
   if (mode == TRACK_ALLOCATION_SITE) {
     BuildCreateAllocationMemento(array,
                                  JSArray::kSize,
                                  allocation_site_payload);
   }
-
-  int elements_location = JSArray::kSize;
-  if (mode == TRACK_ALLOCATION_SITE) {
-    elements_location += AllocationMemento::kSize;
-  }
-
-  HValue* elements = Add<HInnerAllocatedObject>(array, elements_location);
-  Add<HStoreNamedField>(array, HObjectAccess::ForElementsPointer(), elements);
-  return static_cast<HInnerAllocatedObject*>(elements);
 }
 
 
@@ -2679,51 +2681,18 @@ HValue* HGraphBuilder::JSArrayBuilder::EmitInternalMapCode() {
 }
 
 
-HValue* HGraphBuilder::JSArrayBuilder::EstablishAllocationSize(
-    HValue* length_node) {
-  ASSERT(length_node != NULL);
-
+HValue* HGraphBuilder::JSArrayBuilder::EstablishHeaderAllocationSize() {
   int base_size = JSArray::kSize;
   if (mode_ == TRACK_ALLOCATION_SITE) {
     base_size += AllocationMemento::kSize;
   }
-
-  STATIC_ASSERT(FixedDoubleArray::kHeaderSize == FixedArray::kHeaderSize);
-  base_size += FixedArray::kHeaderSize;
-
-  HInstruction* elements_size_value =
-      builder()->Add<HConstant>(elements_size());
-  HInstruction* mul = HMul::NewImul(builder()->zone(), builder()->context(),
-                                    length_node, elements_size_value);
-  builder()->AddInstruction(mul);
-  HInstruction* base = builder()->Add<HConstant>(base_size);
-  HInstruction* total_size = HAdd::New(builder()->zone(), builder()->context(),
-                                       base, mul);
-  total_size->ClearFlag(HValue::kCanOverflow);
-  builder()->AddInstruction(total_size);
-  return total_size;
-}
-
-
-HValue* HGraphBuilder::JSArrayBuilder::EstablishEmptyArrayAllocationSize() {
-  int base_size = JSArray::kSize;
-  if (mode_ == TRACK_ALLOCATION_SITE) {
-    base_size += AllocationMemento::kSize;
-  }
-
-  base_size += IsFastDoubleElementsKind(kind_)
-      ? FixedDoubleArray::SizeFor(initial_capacity())
-      : FixedArray::SizeFor(initial_capacity());
-
   return builder()->Add<HConstant>(base_size);
 }
 
 
 HValue* HGraphBuilder::JSArrayBuilder::AllocateEmptyArray() {
-  HValue* size_in_bytes = EstablishEmptyArrayAllocationSize();
   HConstant* capacity = builder()->Add<HConstant>(initial_capacity());
-  return AllocateArray(size_in_bytes,
-                       capacity,
+  return AllocateArray(capacity,
                        builder()->graph()->GetConstant0());
 }
 
@@ -2731,15 +2700,6 @@ HValue* HGraphBuilder::JSArrayBuilder::AllocateEmptyArray() {
 HValue* HGraphBuilder::JSArrayBuilder::AllocateArray(HValue* capacity,
                                                      HValue* length_field,
                                                      FillMode fill_mode) {
-  HValue* size_in_bytes = EstablishAllocationSize(capacity);
-  return AllocateArray(size_in_bytes, capacity, length_field, fill_mode);
-}
-
-
-HValue* HGraphBuilder::JSArrayBuilder::AllocateArray(HValue* size_in_bytes,
-                                                     HValue* capacity,
-                                                     HValue* length_field,
-                                                     FillMode fill_mode) {
   // These HForceRepresentations are because we store these as fields in the
   // objects we construct, and an int32-to-smi HChange could deopt. Accept
   // the deopt possibility now, before allocation occurs.
@@ -2749,15 +2709,16 @@ HValue* HGraphBuilder::JSArrayBuilder::AllocateArray(HValue* size_in_bytes,
   length_field =
       builder()->AddUncasted<HForceRepresentation>(length_field,
                                                    Representation::Smi());
+
+  // Generate size calculation code here in order to make it dominate
+  // the JSArray allocation.
+  HValue* elms_size = builder()->BuildCalculateElementsSize(kind_, capacity);
+
   // Allocate (dealing with failure appropriately)
-  HAllocate* new_object = builder()->Add<HAllocate>(size_in_bytes,
+  HValue* array_object_size = EstablishHeaderAllocationSize();
+  HAllocate* array_object = builder()->Add<HAllocate>(array_object_size,
       HType::JSArray(), NOT_TENURED, JS_ARRAY_TYPE);
 
-  // Folded array allocation should be aligned if it has fast double elements.
-  if (IsFastDoubleElementsKind(kind_)) {
-     new_object->MakeDoubleAligned();
-  }
-
   // Fill in the fields: map, properties, length
   HValue* map;
   if (allocation_site_payload_ == NULL) {
@@ -2765,22 +2726,30 @@ HValue* HGraphBuilder::JSArrayBuilder::AllocateArray(HValue* size_in_bytes,
   } else {
     map = EmitMapCode();
   }
-  elements_location_ = builder()->BuildJSArrayHeader(new_object,
-                                                     map,
-                                                     mode_,
-                                                     kind_,
-                                                     allocation_site_payload_,
-                                                     length_field);
 
-  // Initialize the elements
+  builder()->BuildJSArrayHeader(array_object,
+                                map,
+                                mode_,
+                                kind_,
+                                allocation_site_payload_,
+                                length_field);
+
+  // Allocate and initialize the elements
+  elements_location_ =
+      builder()->BuildAllocateElements(kind_, elms_size, NOT_TENURED);
+
   builder()->BuildInitializeElementsHeader(elements_location_, kind_, capacity);
 
+  // Set the elements
+  builder()->Add<HStoreNamedField>(
+      array_object, HObjectAccess::ForElementsPointer(), elements_location_);
+
   if (fill_mode == FILL_WITH_HOLE) {
     builder()->BuildFillElementsWithHole(elements_location_, kind_,
                                          graph()->GetConstant0(), capacity);
   }
 
-  return new_object;
+  return array_object;
 }