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Materializing full 64-bit constants on PPC64 can be expensive, requiring up to 5 instructions depending on the locations of the non-zero bits. Sometimes materializing a rotated constant, and then applying the inverse rotation, requires fewer instructions than the direct method. If so, do that instead. In r225132, I added support for forming constants using bit inversion. In effect, this reverts that commit and replaces it with rotation support. The bit inversion is useful for turning constants that are mostly ones into ones that are mostly zeros (thus enabling a more-efficient shift-based materialization), but the same effect can be obtained by using negative constants and a rotate, and that is at least as efficient, if not more. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225135 91177308-0d34-0410-b5e6-96231b3b80d8
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