RFR: 8290154: [JVMCI] partially implement JVMCI for RISC-V [v7]

[Sacha Coppey]

On Tue, 23 Aug 2022 11:29:45 GMT, Sacha Coppey <duke at openjdk.org> wrote:

>> This patch adds a partial JVMCI implementation for RISC-V, to allow using the GraalVM Native Image RISC-V LLVM backend, which does not use JVMCI for code emission.
>> It creates the jdk.vm.ci.riscv64 and jdk.vm.ci.hotspot.riscv64 packages, as well as implements a part of jvmciCodeInstaller_riscv64.cpp. To check for correctness, it enables JVMCI code installation tests on RISC-V. More testing is performed in Native Image.
>
> Sacha Coppey has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix error when emitting LUI and removed vector registers

Do you have details about testing performed in Native Image as mentioned in PR decription?

Yes, the RISC-V LLVM backend for Native Image passes 99% of the tests performed, which is similar to the other LLVM backends.

> I see you added more changes in hotspot file sharedRuntime_riscv.cpp guarded by macro INCLUDE_JVMCI. Searching for INCLUDE_JVMCI or COMPILER2_OR_JVMCI in src/hotspot/cpu/aarch64, I see several more places checking for these macros. Have you checked if we need similar changes for your use case?

I first added the changes for all places where those macros are used, but since only modifying sharedRuntime_riscv.cpp was enough to make the tests pass, I did not wanted to add code that I was not sure was useful at the moment.

> Also could you explain the change made in hotspot file deoptimization.hpp? Thanks.

When the method is inlined, the `if (trap_request < 0)` check behaves incorrectly when the `nmethod` is compiled by JVMCI. Even though the boolean is true, the function returns -11 instead of -1, and the `if (unloaded_class_index >= 0)` checks have the same issue, causing an access to an illegal index of an array. I am not sure why this happens, as it works correctly for method not compiled by JVMCI.

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PR: https://git.openjdk.org/jdk/pull/9587