[Interpreter] Introduce IncStub and DecStub.

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index ba5b97d254e84a06e2757fa5d2840467737c7818..ac6873af182ab10d97324fea74cd060f653de510 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -2796,13 +2796,12 @@ void BytecodeGenerator::VisitCountOperation(CountOperation* expr) {
     }
   }
 
-  // Convert old value into a number.
-  builder()->CastAccumulatorToNumber();
-
   // Save result for postfix expressions.
   if (is_postfix) {
     old_value = register_allocator()->outer()->NewRegister();
-    builder()->StoreAccumulatorInRegister(old_value);
+
+    // Convert old value into a number before saving it.
+    builder()->CastAccumulatorToNumber().StoreAccumulatorInRegister(old_value);
   }
 
   // Perform +1/-1 operation.