[riscv-port] RFR: 8278994: riscv: RVC support [v8]

[Fei Yang]

On Thu, 6 Jan 2022 09:30:19 GMT, Xiaolin Zheng <xlinzheng at openjdk.org> wrote:

>> Hi team,
>> 
>> This patch includes the basic definition of the RVC instruction set and some cleanups. Tested a simple `test/hotspot/jtreg/compiler/` folder on qemu.
>> 
>> Using `<JAVA_HOME>/bin/java -XX:+UnlockExperimentalVMOptions -XX:+UseRVC -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:PrintAssemblyOptions=no-aliases,numeric -XX:+PrintStubCode -XX:-TieredCompilation` could show RVC instructions.
>> 
>> Thanks,
>> Xiaolin
>
> Xiaolin Zheng has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove remaining macros as discussions

src/hotspot/cpu/riscv/assembler_riscv.hpp line 1345:

> 1343:   protected:
> 1344:     Assembler *_masm;
> 1345:     bool _prev_in_compressible_region;

suggestion: rename to "_saved_in_compressible_region"

src/hotspot/cpu/riscv/assembler_riscv.hpp line 1858:

> 1856: 
> 1857: // --------------------------
> 1858: // sub/subw -> c.sub/c.subw

It's better to move this comment before the if block which does compression.

src/hotspot/cpu/riscv/assembler_riscv.hpp line 1898:

> 1896: private:
> 1897: // some helper functions
> 1898:   bool check_rvc() const {

maybe rename to "bool do_compress"?

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PR: https://git.openjdk.java.net/riscv-port/pull/34