Support reusable boxes for Float32x4 fields

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 22a93dc6dd1d65c597bd5ae1eb9cebfe5caf4f6f..79bb838d407e9600c607f6db9a39ca7fe6ac7321 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -26,6 +26,7 @@
 #include "vm/double_conversion.h"
 #include "vm/exceptions.h"
 #include "vm/flow_graph_builder.h"
+#include "vm/flow_graph_compiler.h"
 #include "vm/growable_array.h"
 #include "vm/heap.h"
 #include "vm/intermediate_language.h"
@@ -6450,9 +6451,11 @@ void Field::set_guarded_list_length(intptr_t list_length) const {
 
 
 bool Field::IsUnboxedField() const {
-  // TODO(johnmccutchan): Add kFloat32x4Cid here.
+  bool valid_class = (guarded_cid() == kDoubleCid) ||
+                     (FlowGraphCompiler::SupportsUnboxedFloat32x4() &&
+                      (guarded_cid() == kFloat32x4Cid));
   return is_unboxing_candidate() && !is_final() && !is_nullable() &&
-         ((guarded_cid() == kDoubleCid));
+         valid_class;
 }