RFR: 8278584: compiler/vectorapi/VectorMaskLoadStoreTest.java failed with "Error: ShouldNotReachHere()"

[Jie Fu]

Hi all,

I'd like to fix the vector_length_encoding error in `long_to_maskLE8_avx` and `long_to_maskGT8_avx`.
Since the input parameter of `vector_length_encoding` [1] is the number of vector bytes (not number of vector bits), I believe we shouldn't `mask_len*8` [2][3].

The patch also removes an useless statement [4].

Testing:
   - vector api tests on Linux/x64-{AVX512, AVX2}

Thanks.
Best regards,
Jie

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L1219
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L9552
[3] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L9568
[4] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86.ad#L9580

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Commit messages:
 - 8278584: compiler/vectorapi/VectorMaskLoadStoreTest.java failed with "Error: ShouldNotReachHere()"

Changes: https://git.openjdk.java.net/jdk/pull/6808/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6808&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278584
  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6808.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6808/head:pull/6808

PR: https://git.openjdk.java.net/jdk/pull/6808