RFR: 8353237: [AArch64] Incorrect result of VectorizedHashCode intrinsic on some hardware

[Aleksei Voitylov]

The root of the problem is that VectorizedHashCode intrinsic introduced by JDK-8341194 is not aware of JDK-8079203. JDK-8079203 generates additional nop with madd instruction on Cortex-A53 as a workaround for Cortex-A53 erratum 835769 "AArch64 multiply-accumulate instruction might produce incorrect result". Current VectorizedHashCode intrinsic calculates byte offset to jump inside the unrolled loop code. It assumes 2 instructions per each unrolled iteration (load and madd). JDK-8079203 adds additional nop for Cortex-A53, which breaks offset calculation logic.
 
Current offset calculation logic is using shift instead of multiplication, power-of-2 number instructions are present in each unrolled loop iteration. To keep it simple, this fix adds one more nop into each loop iteration on Cortex-A53 in order to have 4 instruction per iteration, which is also a power-of-2. To account for that, the shift argument for offset calculation logic is increased by 1, because each loop iteration has 2 times more instructions on Cortex-A53.
 
This fix is tested on Raspberry Pi 3 (based on Cortex-A53) by running initially reported application and by running hotspot jtreg tests (not a single test could be run on Cortex-A53 before the fix). The performance gain from the intrinsic is also observed on Cortex-A53 using the ArraysHashCode benchmark.

-------------

Commit messages:
 - account for 835769 errata on Cortex A53 in VectorizedHashCode intrinsic

Changes: https://git.openjdk.org/jdk/pull/24489/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24489&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353237
  Stats: 14 lines in 2 files changed: 12 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/24489.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24489/head:pull/24489

PR: https://git.openjdk.org/jdk/pull/24489