[llvm] [X86] Remove redundant TEST after shifts when count is non-zero (PR #169069)

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GrumpyPigSkin wrote:

@RKSimon I have made the changes to make the optimisation only when optimising for size :) The ISDX86 nodes need to stay I think since the ISD versions don't produce an output for flags.

https://github.com/llvm/llvm-project/pull/169069