[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 71e9eefd17fa76831a0669c5e98c5ff29bffa650..7184959d98f01c20219d1e2dbd2d41e91e370739 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -2801,13 +2801,12 @@ 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.