RFR: 8347917: AArch64: Enable upper GPR registers in C1 [v4]

[Andrew Haley]

On Thu, 13 Feb 2025 09:32:49 GMT, Dmitry Chuyko <dchuyko at openjdk.org> wrote:

> Speculatively it's like having that call costs ~4ns/op, and preserving unnecessary values costs extra ~1ns/op. Preserving unnecessary values also costs a lot of instructions.
> 
> This is definitely a subject for a separate further study, I just checked that if we can observe any difference in benchmarks (yes), and is reversing allocation order currently enough to help (no).

OK, I get it. So it's not clear whether this is worth addressing in C1, and maybe someone will get around to it when higher-priority tasks are dealt with. Thanks.

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PR Comment: https://git.openjdk.org/jdk/pull/23152#issuecomment-2656083808