[jdk17u-dev] RFR: 8309502: RISC-V: String.indexOf intrinsic may produce misaligned memory loads

[Olga Mikhaltsova]

I'd like to backport JDK-8309502 to jdk17u. This fix is related only to RISC-V.

The patch applies almost cleanly except `src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp` because of deletion an empty line at the end in the original patch.

Testing: tier1 tests successfully passed on a RISC-V HiFive board with Linux.

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Commit messages:
 - Backport 6b942893868fa1a64977288bdbdb1bbff8bd9d9c

Changes: https://git.openjdk.org/jdk17u-dev/pull/1857/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1857&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309502
  Stats: 83 lines in 3 files changed: 67 ins; 5 del; 11 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1857.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1857/head:pull/1857

PR: https://git.openjdk.org/jdk17u-dev/pull/1857