RFR: 8333647: C2 SuperWord: some additional PopulateIndex tests [v2]

[Emanuel Peter]

> When I did the deep refactoring in https://github.com/openjdk/jdk/pull/19261, I wanted some more tests for `PopulateIndex`. I push them separately to keep the other RFE smaller.
> 
> I filed a follow-up RFE for some cases that do not vectorize: https://bugs.openjdk.org/browse/JDK-8332878

Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:

  copyright

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19558/files
  - new: https://git.openjdk.org/jdk/pull/19558/files/a4c9f631..e73f3bb4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19558&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19558&range=00-01

  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19558.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19558/head:pull/19558

PR: https://git.openjdk.org/jdk/pull/19558