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d0745cae2f
This was discussed in D48401 as another improvement for: https://bugs.llvm.org/show_bug.cgi?id=37806 If we have 2 different variable values, then we shuffle (select) those lanes, shuffle (select) the constants, and then perform the binop. This eliminates a binop. The new shuffle uses the same shuffle mask as the existing shuffle, so there's no danger of creating a difficult shuffle. All of the earlier constraints still apply, but we also check for extra uses to avoid creating more instructions than we'll remove. Additionally, we're disallowing the fold for div/rem because that could expose a UB hole. Differential Revision: https://reviews.llvm.org/D48678 llvm-svn: 335974
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