[riscv-port] RFR: 8278337: riscv: remove unnecessary ld/sd zr around calls [v3]

[Fei Yang]

On Wed, 8 Dec 2021 12:53:14 GMT, kuaiwei <duke at openjdk.java.net> wrote:

>> It seems zr(x0) is used as stack alignment when saving/restoring registers around calls. But it's unnecessary to ld/st x0 from/to stack. We just need reserve a stack slot in case alignment is required.
>
> kuaiwei has updated the pull request incrementally with one additional commit since the last revision:
>
>   fix code style

Looks good.

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Marked as reviewed by fyang (Lead).

PR: https://git.openjdk.java.net/riscv-port/pull/25