Enable double alignment for constructed arrays.

src/hydrogen.cc

 // Copyright 2013 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 2108 matching lines @@
   // objects we construct, and an int32-to-smi HChange could deopt. Accept
   // the deopt possibility now, before allocation occurs.
   capacity = builder()->Add<HForceRepresentation>(capacity,
                                                   Representation::Smi());
   length_field = builder()->Add<HForceRepresentation>(length_field,
                                                       Representation::Smi());
   // Allocate (dealing with failure appropriately)
   HAllocate* new_object = builder()->Add<HAllocate>(size_in_bytes,
       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) {
     map = EmitInternalMapCode();
   } else {
     map = EmitMapCode();
   }
   elements_location_ = builder()->BuildJSArrayHeader(new_object,
                                                      map,
                                                      mode_,
@@ skipping 7675 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal