[interpreter] Don't keep postfix result if only visited for effect

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 ba0db0c9e4c81455dc9d080285da9154f926a5aa..3cf25b982d7865ef5724d9856728e0fa9cc89f92 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -2782,8 +2782,7 @@ void BytecodeGenerator::VisitCountOperation(CountOperation* expr) {
   Property* property = expr->expression()->AsProperty();
   LhsKind assign_type = Property::GetAssignType(property);
 
-  // TODO(rmcilroy): Set is_postfix to false if visiting for effect.
-  bool is_postfix = expr->is_postfix();
+  bool is_postfix = expr->is_postfix() && !execution_result()->IsEffect();
 
   // Evaluate LHS expression and get old value.
   Register object, home_object, key, old_value, value;