Introduce basic type feedback for for-in statements to avoid deopts.

src/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 951 matching lines @@
   __ push(rax);  // Map.
   __ push(rdx);  // Enumeration cache.
   __ movq(rax, FieldOperand(rdx, FixedArray::kLengthOffset));
   __ push(rax);  // Enumeration cache length (as smi).
   __ Push(Smi::FromInt(0));  // Initial index.
   __ jmp(&loop);
 
   // We got a fixed array in register rax. Iterate through that.
   Label non_proxy;
   __ bind(&fixed_array);
+
+  Handle<JSGlobalPropertyCell> cell =
+      isolate()->factory()->NewJSGlobalPropertyCell(
+          Handle<Object>(
+              Smi::FromInt(TypeFeedbackCells::kForInFastCaseMarker)));
+  RecordTypeFeedbackCell(stmt->PrepareId(), cell);
+  __ LoadHeapObject(rbx, cell);
+  __ Move(FieldOperand(rbx, JSGlobalPropertyCell::kValueOffset),
+          Smi::FromInt(TypeFeedbackCells::kForInSlowCaseMarker));
+
   __ Move(rbx, Smi::FromInt(1));  // Smi indicates slow check
   __ movq(rcx, Operand(rsp, 0 * kPointerSize));  // Get enumerated object
   STATIC_ASSERT(FIRST_JS_PROXY_TYPE == FIRST_SPEC_OBJECT_TYPE);
   __ CmpObjectType(rcx, LAST_JS_PROXY_TYPE, rcx);
   __ j(above, &non_proxy);
   __ Move(rbx, Smi::FromInt(0));  // Zero indicates proxy
   __ bind(&non_proxy);
   __ push(rbx);  // Smi
   __ push(rax);  // Array
   __ movq(rax, FieldOperand(rax, FixedArray::kLengthOffset));
@@ skipping 3371 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64