[jdk17u-dev] RFR: 8279622: C2: miscompilation of map pattern as a vector reduction

[Goetz Lindenmaier]

I backport this for parity with 17.0.5-oracle.

I had to resolve superword.cpp.
Only adding an assertions there, context differs.

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Commit messages:
 - Backport 6fcd322258e0cce3724a4a8dc18f7802018a7cc9

Changes: https://git.openjdk.org/jdk17u-dev/pull/494/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=494&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8279622
  Stats: 95 lines in 5 files changed: 95 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/494.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/494/head:pull/494

PR: https://git.openjdk.org/jdk17u-dev/pull/494