Maintain a FixedArray for the optimized code map.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 99a8f59046793e78b22b85c70fb7d91f6faaf02c..4bdce590610c37dd6e49c38548e994a243002ac1 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6477,8 +6477,8 @@ class SharedFunctionInfo: public HeapObject {
   inline void ReplaceCode(Code* code);
 
   // [optimized_code_map]: Map from native context to optimized code
-  // and a shared literals array or Smi(0) if none.
-  DECL_ACCESSORS(optimized_code_map, Object)
+  // and a shared literals array.
+  DECL_ACCESSORS(optimized_code_map, FixedArray)
 
   // Returns entry from optimized code map for specified context and OSR entry.
   // Note that {code == nullptr, literals == nullptr} indicates no matching
@@ -6490,6 +6490,11 @@ class SharedFunctionInfo: public HeapObject {
   // Clear optimized code map.
   void ClearOptimizedCodeMap();
 
+  // We have a special root FixedArray with the right shape and values
+  // to represent the cleared optimized code map. This predicate checks
+  // if that root is installed.
+  inline bool OptimizedCodeMapIsCleared() const;
+
   // Removes a specific optimized code object from the optimized code map.
   // In case of non-OSR the code reference is cleared from the cache entry but
   // the entry itself is left in the map in order to proceed sharing literals.