It's been a long time since I've messed with Java bytecode [1], but shouldn't the private method call use INVOKESPECIAL?
In general I don't think you can do this to INVOKEVIRTUAL (or INVOKEINTERFACE) as it covers cases where your target is not statically resolved (virtual/interface calls). This transformation should be limited to INVOKESTATIC and INVOKESPECIAL.
You also need lots more checks to make sure you can apply the transformations, like ensure the call site is not covered by a try block, otherwise this is not semantics preserving.
In general I don't think you can do this to INVOKEVIRTUAL (or INVOKEINTERFACE) as it covers cases where your target is not statically resolved (virtual/interface calls). This transformation should be limited to INVOKESTATIC and INVOKESPECIAL.
You also need lots more checks to make sure you can apply the transformations, like ensure the call site is not covered by a try block, otherwise this is not semantics preserving.
1: https://jauvm.blogspot.com/