RFR: 8290280: riscv: Clean up stack and register handling in interpreter

[Andrew Haley]

On Thu, 14 Jul 2022 07:42:57 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

> As [JDK-8288971](https://bugs.openjdk.org/browse/JDK-8288971) described, we have the same issue on riscv backend:
> 
> 1. We use x30 to pass the caller's SP to a callee through adapters. x30 is not a callee-saved register in native ABI [1], we choose x19 for this patch.
> 2. We frequently recalculate the location where the native SP needs to go. We have a spare slot in the interpreter frame, so we should calculate it once, when the frame is created, and use it.
> 3. Relate to 1, we should clearly label all the places where the caller's SP is passed to a callee.
> 
> [1]. https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc
> 
> Additional tests:
> - hotspot/jdk tier1 on  QEMU with Release JDK
> - hotspot tier1 on HiFive Unmatched board with Release JDK
> - hotspot tier1 on QEMU with Fastdebug JDK

This looks reasonable. Don't forget that JDK-8289698 will be needed when you have support for virtual threads.

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PR: https://git.openjdk.org/jdk/pull/9487