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Updating D141348: [X86][CodeGen]Fix extract f16 from big vectors

Fix extract f16 from big vectors

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In D139685#3983239, @HaohaiWen wrote:

Now, when llc encounters the case that contains a lot of extract_vector_elt and a BUILD_VECTOR, it will replace these to vector_shuffle to decrease the size of code, the actions are done in createBuildVecShuffle in DAGCombiner.cpp, but now the code cannot handle the case that the size of source vector reg is more than twice the dest size.

Better to limit column width to 80.

Now, when llc encounters the case that contains a lot of
extract_vector_elt and a BUILD_VECTOR, it will replace these to
vector_shuffle to decrease the size of code, the actions are done in
createBuildVecShuffle in DAGCombiner.cpp, but now the code cannot handle
the case that the size of source vector reg is more than twice the dest
size.