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

runtime/vm/intermediate_language_mips.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/compiler.h"
@@ skipping 1623 matching lines @@
       locs()->temp(locs()->temp_count() - 1).reg() : kNoRegister;
 
   Label ok, fail_label;
 
   Label* deopt = compiler->is_optimizing() ?
       compiler->AddDeoptStub(deopt_id(), ICData::kDeoptGuardField) : NULL;
 
   Label* fail = (deopt != NULL) ? deopt : &fail_label;
 
   if (emit_full_guard) {
-    __ LoadObject(field_reg, Field::ZoneHandle(field().raw()));
+    __ LoadObject(field_reg, Field::ZoneHandle(field().Original()));
 
     FieldAddress field_cid_operand(field_reg, Field::guarded_cid_offset());
     FieldAddress field_nullability_operand(
         field_reg, Field::is_nullable_offset());
 
     if (value_cid == kDynamicCid) {
       LoadValueCid(compiler, value_cid_reg, value_reg);
 
       __ lhu(CMPRES1, field_cid_operand);
       __ beq(value_cid_reg, CMPRES1, &ok);
@@ skipping 124 matching lines @@
       compiler->AddDeoptStub(deopt_id(), ICData::kDeoptGuardField) : NULL;
 
   const Register value_reg = locs()->in(0).reg();
 
   if (!compiler->is_optimizing() ||
       (field().guarded_list_length() == Field::kUnknownFixedLength)) {
     const Register field_reg = locs()->temp(0).reg();
 
     Label ok;
 
-    __ LoadObject(field_reg, Field::ZoneHandle(field().raw()));
+    __ LoadObject(field_reg, Field::ZoneHandle(field().Original()));
 
     __ lb(CMPRES1, FieldAddress(field_reg,
         Field::guarded_list_length_in_object_offset_offset()));
     __ blez(CMPRES1, &ok);
 
     __ lw(CMPRES2, FieldAddress(field_reg,
         Field::guarded_list_length_offset()));
 
     // Load the length from the value. GuardFieldClass already verified that
     // value's class matches guarded class id of the field.
@@ skipping 194 matching lines @@
 
     if (ShouldEmitStoreBarrier()) {
       // Value input is a writable register and should be manually preserved
       // across allocation slow-path.
       locs()->live_registers()->Add(locs()->in(1), kTagged);
     }
 
     Label store_pointer;
     Label store_double;
 
-    __ LoadObject(temp, Field::ZoneHandle(field().raw()));
+    __ LoadObject(temp, *field().OriginalAsHandle(compiler->zone()));

[siva, 2016/02/25 23:38:33]

Ditto.

 
     __ lhu(temp2, FieldAddress(temp, Field::is_nullable_offset()));
     __ BranchEqual(temp2, Immediate(kNullCid), &store_pointer);
 
     __ lbu(temp2, FieldAddress(temp, Field::kind_bits_offset()));
     __ andi(CMPRES1, temp2, Immediate(1 << Field::kUnboxingCandidateBit));
     __ beq(CMPRES1, ZR, &store_pointer);
 
     __ lhu(temp2, FieldAddress(temp, Field::guarded_cid_offset()));
     __ BranchEqual(temp2, Immediate(kDoubleCid), &store_double);
@@ skipping 85 matching lines @@
   locs->set_temp(0, Location::RequiresRegister());
   return locs;
 }
 
 
 void StoreStaticFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ Comment("StoreStaticFieldInstr");
   Register value = locs()->in(0).reg();
   Register temp = locs()->temp(0).reg();
 
-  __ LoadObject(temp, field());
+  __ LoadObject(temp, *field().OriginalAsHandle(compiler->zone()));

[siva, 2016/02/25 23:38:33]

Ditto.

   if (this->value()->NeedsStoreBuffer()) {
     __ StoreIntoObject(temp,
                        FieldAddress(temp, Field::static_value_offset()),
                        value,
                        CanValueBeSmi());
   } else {
     __ StoreIntoObjectNoBarrier(
         temp, FieldAddress(temp, Field::static_value_offset()), value);
   }
 }
@@ skipping 189 matching lines @@
 
   Label done;
   Register result_reg = locs()->out(0).reg();
   if (IsPotentialUnboxedLoad()) {
     Register temp = locs()->temp(1).reg();
     DRegister value = locs()->temp(0).fpu_reg();
 
     Label load_pointer;
     Label load_double;
 
-    __ LoadObject(result_reg, Field::ZoneHandle(field()->raw()));
+    __ LoadObject(result_reg, Field::ZoneHandle(field()->Original()));
 
     FieldAddress field_cid_operand(result_reg, Field::guarded_cid_offset());
     FieldAddress field_nullability_operand(result_reg,
                                            Field::is_nullable_offset());
 
     __ lhu(temp, field_nullability_operand);
     __ BranchEqual(temp, Immediate(kNullCid), &load_pointer);
 
     __ lhu(temp, field_cid_operand);
     __ BranchEqual(temp, Immediate(kDoubleCid), &load_double);
@@ skipping 3266 matching lines @@
                                 1,
                                 locs());
   __ lw(result, Address(SP, 1 * kWordSize));
   __ addiu(SP, SP, Immediate(2 * kWordSize));
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS