[RISCV][ISel] Optimize setcc with mask test idioms (#147015) As we are converting more comparisons/differences of pointers into those of offsets in InstCombine, the mask test idiom `icmp eq/ne (and X, Mask), 0` may be more common in real-world programs. This patch eliminates unnecessary srli instructions for this pattern. We have a similar optimization for `RISCVISD::SELECT_CC/BR_CC`: https://github.com/llvm/llvm-project/blob/a89e232058a29260eb9bfe77b862715ce875f962/llvm/lib/Target/RISCV/RISCVISelLowering.cpp#L2416-L2446 However, I cannot reuse the function `translateSetCCForBranch` due to some regressions caused by other DAGCombiner folds: https://github.com/llvm/llvm-project/compare/main...dtcxzyw:llvm-project:rv-mask-test. So this patch defers the transformation to ISel.
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