[for-in] Ensure that we learn from deopts within for-in loop bodies.

src/full-codegen/x64/full-codegen-x64.cc

 // Copyright 2012 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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/ast/scopes.h"
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
@@ skipping 1050 matching lines @@
   __ jmp(&loop);
 
   __ bind(&no_descriptors);
   __ addp(rsp, Immediate(kPointerSize));
   __ jmp(&exit);
 
   // We got a fixed array in register rax. Iterate through that.
   __ bind(&fixed_array);
 
   // No need for a write barrier, we are storing a Smi in the feedback vector.
+  int const vector_index = SmiFromSlot(slot)->value();
   __ EmitLoadTypeFeedbackVector(rbx);
-  int vector_index = SmiFromSlot(slot)->value();
   __ Move(FieldOperand(rbx, FixedArray::OffsetOfElementAt(vector_index)),
           TypeFeedbackVector::MegamorphicSentinel(isolate()));
   __ movp(rcx, Operand(rsp, 0 * kPointerSize));  // Get enumerated object
   __ Push(Smi::FromInt(1));                      // Smi(1) indicates slow check
   __ Push(rax);  // Array
   __ movp(rax, FieldOperand(rax, FixedArray::kLengthOffset));
   __ Push(rax);  // Fixed array length (as smi).
   PrepareForBailoutForId(stmt->PrepareId(), NO_REGISTERS);
   __ Push(Smi::FromInt(0));  // Initial index.
 
@@ skipping 17 matching lines @@
   // permanent slow case into register rdx.
   __ movp(rdx, Operand(rsp, 3 * kPointerSize));
 
   // Check if the expected map still matches that of the enumerable.
   // If not, we may have to filter the key.
   Label update_each;
   __ movp(rcx, Operand(rsp, 4 * kPointerSize));
   __ cmpp(rdx, FieldOperand(rcx, HeapObject::kMapOffset));
   __ j(equal, &update_each, Label::kNear);
 
+  // We might get here from TurboFan or Crankshaft when something in the
+  // for-in loop body deopts and only now notice in fullcodegen, that we
+  // can now longer use the enum cache, i.e. left fast mode. So better record
+  // this information here, in case we later OSR back into this loop or
+  // reoptimize the whole function w/o rerunning the loop with the slow
+  // mode object in fullcodegen (which would result in a deopt loop).
+  __ EmitLoadTypeFeedbackVector(rdx);
+  __ Move(FieldOperand(rdx, FixedArray::OffsetOfElementAt(vector_index)),
+          TypeFeedbackVector::MegamorphicSentinel(isolate()));
+
   // Convert the entry to a string or null if it isn't a property
   // anymore. If the property has been removed while iterating, we
   // just skip it.
   __ Push(rcx);  // Enumerable.
   __ Push(rbx);  // Current entry.
   __ CallRuntime(Runtime::kForInFilter);
   PrepareForBailoutForId(stmt->FilterId(), TOS_REG);
   __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
   __ j(equal, loop_statement.continue_label());
   __ movp(rbx, rax);
@@ skipping 3605 matching lines @@
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64