[jdk21u-dev] RFR: 8333890: Fatal error in auto-vectorizer with float16 kernel.

[Satyen Subramaniam]

Backporting JDK-8333890: Fatal error in auto-vectorizer with float16 kernel. Fixes an assertion failure seen while auto-vectorizing conversion chain involving float16 type by constraining the container type for ConvF2HF IR to short type upfront. Adds test to confirm.

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Commit messages:
 - Backport 55fd1ed228ea3c42aaf92579e5dcb818fe14351d

Changes: https://git.openjdk.org/jdk21u-dev/pull/1549/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1549&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333890
  Stats: 71 lines in 2 files changed: 71 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1549.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1549/head:pull/1549

PR: https://git.openjdk.org/jdk21u-dev/pull/1549