Enhancement to InstCombine. Try to catch this opportunity:
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((X^C1) >> C2) ^ C3 => (X>>C2) ^ ((C1>>C2)^C3)
where the subexpression "X ^ C1" has more than one uses, and
"(X^C1) >> C2" has single use.
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Reviewed by Nadav (with minor change per his request).
llvm-svn: 168615
38196f1ebf