RFR: 8338126 : C2 SuperWord: VectorCastF2HF / vcvtps2ph produces wrong results for vector length 2 [v4]

[Sandhya Viswanathan]

> When Float.floatToFloat16 is vectorized using a 2-element vector width due to dependencies, we incorrectly generate a 4-element vcvtps2ph with memory as destination storing 8 bytes instead of desired 4 bytes.  This issue is fixed in this PR by limiting the memory version of match rule to 4-element vector and above.
> Also a regression test case is added accordingly.
> 
> Best Regards,
> Sandhya

Sandhya Viswanathan has updated the pull request incrementally with one additional commit since the last revision:

  Review comments resolution

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21480/files
  - new: https://git.openjdk.org/jdk/pull/21480/files/f2981374..c876dc95

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21480&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21480&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21480.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21480/head:pull/21480

PR: https://git.openjdk.org/jdk/pull/21480