[DAGCombiner] Bug 31275- Extract a shift from a constant mul or udiv if a rotate...

[DAGCombiner] Bug 31275- Extract a shift from a constant mul or udiv if a rotate can be formed

Summary:
Attempt to extract a shrl from a udiv or a shl from a mul if this allows a rotate to be formed.  This targets cases where the input to a rotate pattern was a mul or udiv by a constant and InstCombine merged one of the shifts with the op.

Patch by: sameconrad (Sam Conrad)

Reviewers: RKSimon, craig.topper, spatel, lebedev.ri, javed.absar

Reviewed By: lebedev.ri

Subscribers: efriedma, kparzysz, llvm-commits

Differential Revision: https://reviews.llvm.org/D47681

llvm-svn: 338270