Currently, all class fields are mutable at the Wasm level: thegenFunctionID.newDefault function creates a class instance with fields initialized to their zero values, and then the constructor initializes them (byAssign at the IR level).

Fields being mutable means that accessing a field is an impure operation at the Wasm level, causing us to miss some optimization opportunities.
In fact, making itables immutable has improved performance in some benchmarks, as seen in#5038.

We may want to "merge" thegenFunctionID.newDefault function with the constructor: The fused constructor would:

• Set up the vtable (virtual method table) and itable (interface table)
• Initialize the fields
  • Instead of filling fields with zero values, thewasmemitter would transform the RHS of fieldAssign nodes to become the initial values of the fields.
• Executestruct.new for instantiation (asnewDefault currently does)

Alternatively, should we modify the IR structure somehow? It appears that theseAssign operations in the constructor originate from Scala compiler, not fromGenJSCode🤷. In this case, making changes at the IR level seems introduce more complications than it solves.