Revert r31326.

runtime/vm/intermediate_language_x64.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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 1170 matching lines @@
   Register field_reg = needs_field_temp_reg ?
       locs()->temp(locs()->temp_count() - 1).reg() : kNoRegister;
 
   Label ok, fail_label;
 
   Label* deopt = compiler->is_optimizing() ?
       compiler->AddDeoptStub(deopt_id(), kDeoptGuardField) : NULL;
 
   Label* fail = (deopt != NULL) ? deopt : &fail_label;
 
+  const bool ok_is_fall_through = (deopt != NULL);
+
   if (!compiler->is_optimizing() || (field_cid == kIllegalCid)) {
     if (!compiler->is_optimizing() && (field_reg == kNoRegister)) {
       // Currently we can't have different location summaries for optimized
       // and non-optimized code. So instead we manually pick up a register
       // that is known to be free because we know how non-optimizing compiler
       // allocates registers.
       field_reg = RBX;
       ASSERT((field_reg != value_reg) && (field_reg != value_cid_reg));
     }
 
@@ skipping 177 matching lines @@
           // Destroy value_cid_reg (safe because we are finished with it).
           __ movq(value_cid_reg,
                   FieldAddress(value_reg, TypedData::length_offset()));
           __ movq(field_length_operand, value_cid_reg);
         } else {
           __ LoadImmediate(field_length_operand,
                   Immediate(Smi::RawValue(Field::kNoFixedLength)), PP);
         }
       }
     }
+    if (!ok_is_fall_through) {
+      __ jmp(&ok);
+    }
 
     if (deopt == NULL) {
       ASSERT(!compiler->is_optimizing());
-      __ jmp(&ok);
       __ Bind(fail);
 
       __ CompareImmediate(FieldAddress(field_reg, Field::guarded_cid_offset()),
                           Immediate(kDynamicCid), PP);
       __ j(EQUAL, &ok);
 
       __ pushq(field_reg);
       __ pushq(value_reg);
       __ CallRuntime(kUpdateFieldCidRuntimeEntry, 2);
       __ Drop(2);  // Drop the field and the value.
     }
   } else {
     ASSERT(compiler->is_optimizing());
     ASSERT(deopt != NULL);
+    ASSERT(ok_is_fall_through);
     // Field guard class has been initialized and is known.
     if (field_reg != kNoRegister) {
       __ LoadObject(field_reg, Field::ZoneHandle(field().raw()), PP);
     }
 
     if (value_cid == kDynamicCid) {
       // Field's guarded class id is fixed but value's class id is not known.
       __ testq(value_reg, Immediate(kSmiTagMask));
 
       if (field_cid != kSmiCid) {
@@ skipping 3518 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64