[llvm] [X86] Remove TuningFastVariableCrossLaneShuffle from X86_64V4Tuning (PR #212178)

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222rohan wrote:

> @222rohan I'm confused when looking at the configurations you mentioned. One mentioned AOCC and one ICC. Did you collect results from these compilers instead of community LLVM?

We used the community LLVM. But since we couldn't reproduce the your results on 881 and 362 with the standard config (`-O3 -flto -march=x86-64-v4`), we tried to derive options from these additional configs mentioned above to see if a specific option/runtime settings was causing a difference. 
(by derive, I meant, for ex: `-qopt-zmm-usage=high` --> `-mprefer-vector-width=512` from the ICC config)

But given your note that you used the downstream compiler, that likely explains the discrepancy.

https://github.com/llvm/llvm-project/pull/212178