As described in jvms25[1], the index of bytecode aastore should be type of `int`. We should use the `lw` instruction (which loads a 32-bit index from the operand stack and performs sign extension) instead of the `ld` instruction.

1. https://docs.oracle.com/javase/specs/jvms/se25/html/jvms-6.html#jvms-6.5.aastore