RFR: 8340241: RISC-V: Returns mispredicted [v15]

[Fei Yang]

On Wed, 16 Oct 2024 14:10:00 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> Note sure what you mean by "t0 and t1 is reserved from C2". They are not allocatable by register allocator. But C2 think there is RFLAG register (still not allocatable), which we have aliased with x6/t1. This pseudo register will be SOC. Any live SOC should be pushed before a call.

Yeah, they are not allocatable. That's what I mean by saying they are reserved :-)

> The clobbering we added for CallRuntime/CallDynamicJava is not needed AFAIK, check e.g. x86 it do not kill CR as RFLAG is also set to SOC on x86 (but here backed with a real register).

Yes, I also checked other CPU platforms and I think you are right in that these effect of killing CR are unnecessary. Maybe a separate PR to clean them up.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21406#discussion_r1803232561