Reland "Add basic crankshaft support for slow-mode for-in to avoid disabling optimizations"

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 5754 matching lines @@
   // backpatching it with the spill slot operands.
   DCHECK(!environment->HasBeenRegistered());
   RegisterEnvironmentForDeoptimization(environment, Safepoint::kNoLazyDeopt);
 
   GenerateOsrPrologue();
 }
 
 
 void LCodeGen::DoForInPrepareMap(LForInPrepareMap* instr) {
   DCHECK(ToRegister(instr->context()).is(rsi));
-  __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
-  DeoptimizeIf(equal, instr, Deoptimizer::kUndefined);
 
-  Register null_value = rdi;
-  __ LoadRoot(null_value, Heap::kNullValueRootIndex);
-  __ cmpp(rax, null_value);
   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);
   __ CheckEnumCache(null_value, &call_runtime);
 
   __ movp(rax, FieldOperand(rax, HeapObject::kMapOffset));
   __ jmp(&use_cache, Label::kNear);
 
   // Get the set of properties to enumerate.
   __ bind(&call_runtime);
   __ Push(rax);
   CallRuntime(Runtime::kGetPropertyNamesFast, 1, instr);
 
@@ skipping 118 matching lines @@
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64