Disallow updates to ic_with_type_info_count with negative values.

src/objects-inl.h

 // 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 5223 matching lines @@
 
 
 int TypeFeedbackInfo::ic_with_type_info_count() {
   int current = Smi::cast(READ_FIELD(this, kStorage2Offset))->value();
   return ICsWithTypeInfoCountField::decode(current);
 }
 
 
 void TypeFeedbackInfo::change_ic_with_type_info_count(int delta) {
   int value = Smi::cast(READ_FIELD(this, kStorage2Offset))->value();
-  int current_count = ICsWithTypeInfoCountField::decode(value);
-  value =
-      ICsWithTypeInfoCountField::update(value, current_count + delta);
-  WRITE_FIELD(this, kStorage2Offset, Smi::FromInt(value));
+  int new_count = ICsWithTypeInfoCountField::decode(value) + delta;
+  // We can get negative count here when the type-feedback info is
+  // shared between two code objects. The can only happen when
+  // the debugger made a shallow copy of code object (see Heap::CopyCode).
+  // Since we do not optimize when the debugger is active, we can skip
+  // this counter update.
+  if (new_count >= 0) {
+    new_count &= ICsWithTypeInfoCountField::kMask;
+    value = ICsWithTypeInfoCountField::update(value, new_count);
+    WRITE_FIELD(this, kStorage2Offset, Smi::FromInt(value));
+  }
 }
 
 
 void TypeFeedbackInfo::initialize_storage() {
   WRITE_FIELD(this, kStorage1Offset, Smi::FromInt(0));
   WRITE_FIELD(this, kStorage2Offset, Smi::FromInt(0));
 }
 
 
 void TypeFeedbackInfo::change_own_type_change_checksum() {
@@ skipping 143 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_