[riscv-port] RFR: 8276989: riscv: C1 should not allocate x3, which is the gp register

[zhengxiaolinX]

On Thu, 11 Nov 2021 09:28:13 GMT, zhengxiaolinX <duke at openjdk.java.net> wrote:

> Hi team,
> 
> x3 is a special register on RISCV and we should not use it as a register allocation candidate - if users write JNI programs referencing global variables, where ld could link global reference loading logic to an instruction like 'ld $Rtmp, $offset(x3)', and try to call vm functions, C1 will zap x3's value and causes a crash. It seems C2 doesn't use x3 so we are just aligning the logic with C2 properly.
> 
> Thanks,
> Xiaolin

Thanks for the reviews, Fei and Aleksey. Seems I could integrate this patch and this repo's bot may need some minor adjustment in configuration.

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PR: https://git.openjdk.java.net/riscv-port/pull/3