[jdk11u-dev] RFR: 8258946: Fix optimization-unstable code involving signed integer overflow

[Goetz Lindenmaier]

I backport this for parity with 11.0.17-oracle.

Clean excpet for Copyright.  Will mark as /clean.

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Commit messages:
 - Backport dd8996c5f5784b18a01a86354e3ccaae1f86adae

Changes: https://git.openjdk.org/jdk11u-dev/pull/1272/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1272&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8258946
  Stats: 10 lines in 3 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1272.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1272/head:pull/1272

PR: https://git.openjdk.org/jdk11u-dev/pull/1272