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This change adds transformations such as: zext(or(setcc(eq, (cmp x, 0)), setcc(eq, (cmp y, 0)))) To: srl(or(ctlz(x), ctlz(y)), log2(bitsize(x)) This optimisation is beneficial on Jaguar architecture only, where lzcnt has a good reciprocal throughput. Other architectures such as Intel's Haswell/Broadwell or AMD's Bulldozer/PileDriver do not benefit from it. For this reason the change also adds a "HasFastLZCNT" feature which gets enabled for Jaguar. Differential Revision: https://reviews.llvm.org/D23446 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284248 91177308-0d34-0410-b5e6-96231b3b80d8
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