[riscv-port-jdk17u:riscv-port] RFR: 8305728: RISC-V: Use bexti instruction to do single-bit testing

[Fei Yang]

On Thu, 1 Jun 2023 09:30:05 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Hi, please review this backport to riscv-port-jdk17u.
> Backport of [JDK-8305728](https://bugs.openjdk.org/browse/JDK-8305728). The original patch cannot be directly applied because jdk17u has no [JDK-8299089](https://bugs.openjdk.org/browse/JDK-8299089) and [JDK-8301995](https://bugs.openjdk.org/browse/JDK-8301995).
> 
> Testing:
> - tier1-3 tests on QEMU-System w/ and w/o UseZbs (release build)
> - tier1-3 tests on unmatched board w/o UseZbs (release build)

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 534:

> 532: 
> 533:   // Test for jweak tag.
> 534:   test_bit(t0, value, exact_log2(JNIHandles::weak_tag_mask));

I don't think this is a single-bit testing, right?

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PR Review Comment: https://git.openjdk.org/riscv-port-jdk17u/pull/65#discussion_r1213846687