[jdk17u-dev] RFR: 8299179: ArrayFill with store on backedge needs to reduce length by 1

[Goetz Lindenmaier]

I backport this for parity with 17.0.8-oracle.

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Commit messages:
 - Backport d716ec5d3034240b7dd0aed86d9bb371bc3e5f5a

Changes: https://git.openjdk.org/jdk17u-dev/pull/1269/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1269&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299179
  Stats: 429 lines in 3 files changed: 429 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1269.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1269/head:pull/1269

PR: https://git.openjdk.org/jdk17u-dev/pull/1269