In background compilation make a copy of Field in order to freeze its state

runtime/vm/redundancy_elimination.cc

Index: runtime/vm/redundancy_elimination.cc
diff --git a/runtime/vm/redundancy_elimination.cc b/runtime/vm/redundancy_elimination.cc
index 01a6ce46b012f7305812818774316adf1a3d3073..adc131995d27c87fd9ca5f9c5cdd683056dbd1af 100644
--- a/runtime/vm/redundancy_elimination.cc
+++ b/runtime/vm/redundancy_elimination.cc
@@ -481,12 +481,13 @@ class Place : public ValueObject {
   }
 
   bool SameField(const Place* other) const {
-    return (kind() == kField) ? (field().raw() == other->field().raw())
-                              : (offset_in_bytes_ == other->offset_in_bytes_);
+    return (kind() == kField) ?
+        (field().Original() == other->field().Original()) :
+        (offset_in_bytes_ == other->offset_in_bytes_);
   }
 
   intptr_t FieldHashcode() const {
-    return (kind() == kField) ? reinterpret_cast<intptr_t>(field().raw())
+    return (kind() == kField) ? reinterpret_cast<intptr_t>(field().Original())
                               : offset_in_bytes_;
   }
 
@@ -3085,6 +3086,8 @@ void AllocationSinking::DetachMaterializations() {
 // Add a field/offset to the list of fields if it is not yet present there.
 static bool AddSlot(ZoneGrowableArray<const Object*>* slots,
                     const Object& slot) {
+  ASSERT(slot.IsSmi() || slot.IsField());
+  ASSERT(!slot.IsField() || Field::Cast(slot).IsOriginal());
   for (intptr_t i = 0; i < slots->length(); i++) {
     if ((*slots)[i]->raw() == slot.raw()) {
       return false;
@@ -3281,7 +3284,7 @@ void AllocationSinking::InsertMaterializations(Definition* alloc) {
     StoreInstanceFieldInstr* store = use->instruction()->AsStoreInstanceField();
     if ((store != NULL) && (store->instance()->definition() == alloc)) {
       if (!store->field().IsNull()) {
-        AddSlot(slots, store->field());
+        AddSlot(slots, Field::ZoneHandle(Z, store->field().Original()));
       } else {
         AddSlot(slots, Smi::ZoneHandle(Z, Smi::New(store->offset_in_bytes())));
       }