[riscv-port] RFR: 8277431: riscv: Intrinsify recursive ObjectMonitor locking for C2

[Fei Yang]

On Tue, 23 Nov 2021 07:02:33 GMT, Yadong Wang <yadongwang at openjdk.org> wrote:

> According to https://bugs.openjdk.java.net/browse/JDK-8277180, the C2 fast_lock and fast_unlock intrinsics don't support recursive ObjectMonitor locking. Some workload can significantly benefit from this. This fixes the problem on riscv.
> Tier1 tests of hotspot and jdk are passed on unmatched and all JTreg tests are tested on qemu without new failures.

It would be interesting to know how this may affect performance on riscv. Maybe we can try DaCapo h2 to see.

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PR: https://git.openjdk.java.net/riscv-port/pull/13