As mentioned in https://bugs.openjdk.org/browse/JDK-8285790 regarding the ARM64 vector instruct modifications:
Since the new rules are unique and setting different "ins_cost" makes no sense, we have switched to using the default cost.

Currently, there is a similar situation on RISC-V. Over half of the instructions in riscv_v.ad do not include ins_cost definitions. Additionally, as RVV nodes are also unique, we can unify the format by removing these ins_cost entries from riscv_v.ad.