[builtins] Speed up TypedArrayInitialize in CodeStubAssembler

src/builtins/builtins-typedarray-gen.cc

 // Copyright 2017 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins-utils-gen.h"
 #include "src/builtins/builtins.h"
 #include "src/code-stub-assembler.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 196 matching lines @@
     Node* header_size = IntPtrConstant(FixedTypedArrayBase::kHeaderSize);
     total_size.Bind(IntPtrAdd(SmiToWord(byte_length), header_size));
     Goto(&allocate_elements);
   }
 
   BIND(&allocate_elements);
   {
     // Allocate a FixedTypedArray and set the length, base pointer and external
     // pointer.
     CSA_ASSERT(this, IsRegularHeapObjectSize(total_size.value()));
-    Node* elements = AllocateInNewSpace(total_size.value(), kDoubleAlignment);
+
+    Node* elements;
+    int heap_alignment =
+        ElementSizeLog2Of(MachineType::PointerRepresentation());
+
+    if (UnalignedLoadSupported(MachineType::Float64(), heap_alignment) &&
+        UnalignedStoreSupported(MachineType::Float64(), heap_alignment)) {
+      elements = AllocateInNewSpace(total_size.value());
+    } else {
+      elements = AllocateInNewSpace(total_size.value(), kDoubleAlignment);
+    }
 
     StoreMapNoWriteBarrier(elements, fixed_typed_map.value());
     StoreObjectFieldNoWriteBarrier(elements, FixedArray::kLengthOffset, length);
     StoreObjectFieldNoWriteBarrier(
         elements, FixedTypedArrayBase::kBasePointerOffset, elements);
     StoreObjectFieldNoWriteBarrier(elements,
                                    FixedTypedArrayBase::kExternalPointerOffset,
                                    IntPtrConstant(fta_base_data_offset),
                                    MachineType::PointerRepresentation());
 
@@ skipping 485 matching lines @@
 // ES6 #sec-%typedarray%.prototype.keys
 TF_BUILTIN(TypedArrayPrototypeKeys, TypedArrayBuiltinsAssembler) {
   Node* context = Parameter(Descriptor::kContext);
   Node* receiver = Parameter(Descriptor::kReceiver);
   GenerateTypedArrayPrototypeIterationMethod(
       context, receiver, "%TypedArray%.prototype.keys()", IterationKind::kKeys);
 }
 
 }  // namespace internal
 }  // namespace v8