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

src/full-codegen/arm/full-codegen-arm.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_ARM
 
 #include "src/ast/scopes.h"
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/codegen.h"
@@ skipping 1100 matching lines @@
   __ Push(r2, r1, r0);
   __ jmp(&loop);
 
   __ bind(&no_descriptors);
   __ Drop(1);
   __ jmp(&exit);
 
   // We got a fixed array in register r0. Iterate through that.
   __ bind(&fixed_array);
 
+  int const vector_index = SmiFromSlot(slot)->value();
   __ EmitLoadTypeFeedbackVector(r1);
   __ mov(r2, Operand(TypeFeedbackVector::MegamorphicSentinel(isolate())));
-  int vector_index = SmiFromSlot(slot)->value();
   __ str(r2, FieldMemOperand(r1, FixedArray::OffsetOfElementAt(vector_index)));
   __ mov(r1, Operand(Smi::FromInt(1)));  // Smi(1) indicates slow check
   __ Push(r1, r0);  // Smi and array
   __ ldr(r1, FieldMemOperand(r0, FixedArray::kLengthOffset));
   __ Push(r1);  // Fixed array length (as smi).
   PrepareForBailoutForId(stmt->PrepareId(), NO_REGISTERS);
   __ mov(r0, Operand(Smi::FromInt(0)));
   __ Push(r0);  // Initial index.
 
   // Generate code for doing the condition check.
@@ skipping 15 matching lines @@
   __ ldr(r2, MemOperand(sp, 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;
   __ ldr(r1, MemOperand(sp, 4 * kPointerSize));
   __ ldr(r4, FieldMemOperand(r1, HeapObject::kMapOffset));
   __ cmp(r4, Operand(r2));
   __ b(eq, &update_each);
 
+  // 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(r0);
+  __ mov(r2, Operand(TypeFeedbackVector::MegamorphicSentinel(isolate())));
+  __ str(r2, FieldMemOperand(r0, FixedArray::OffsetOfElementAt(vector_index)));
+
   // Convert the entry to a string or (smi) 0 if it isn't a property
   // any more. If the property has been removed while iterating, we
   // just skip it.
   __ push(r1);  // Enumerable.
   __ push(r3);  // Current entry.
   __ CallRuntime(Runtime::kForInFilter);
   PrepareForBailoutForId(stmt->FilterId(), TOS_REG);
   __ mov(r3, Operand(r0));
   __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
   __ cmp(r0, ip);
@@ skipping 3689 matching lines @@
   DCHECK(interrupt_address ==
          isolate->builtins()->OsrAfterStackCheck()->entry());
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM