[x64] Fix useless deopt in for-in.

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 5866 matching lines @@
   DCHECK(!environment->HasBeenRegistered());
   RegisterEnvironmentForDeoptimization(environment, Safepoint::kNoLazyDeopt);
 
   GenerateOsrPrologue();
 }
 
 
 void LCodeGen::DoForInPrepareMap(LForInPrepareMap* instr) {
   DCHECK(ToRegister(instr->context()).is(rsi));
 
-  DeoptimizeIf(equal, instr, Deoptimizer::kNull);
-
   Condition cc = masm()->CheckSmi(rax);
   DeoptimizeIf(cc, instr, Deoptimizer::kSmi);
 
   STATIC_ASSERT(FIRST_JS_PROXY_TYPE == FIRST_SPEC_OBJECT_TYPE);
   __ CmpObjectType(rax, LAST_JS_PROXY_TYPE, rcx);
   DeoptimizeIf(below_equal, instr, Deoptimizer::kWrongInstanceType);
 
   Label use_cache, call_runtime;
   Register null_value = rdi;
   __ LoadRoot(null_value, Heap::kNullValueRootIndex);
@@ skipping 128 matching lines @@
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64