Re-land: Teach CorrelatedValuePropagation to reduce the width of udiv/urem instructions.

Summary:
If the operands of a udiv/urem can be proved to fit within a smaller
power-of-two-sized type, reduce the width of the udiv/urem.

Backed out for failing an assert in clang bootstrap builds.  Re-landing
with a fix for handling non-power-of-two inputs (e.g. udiv i24).

Original Differential Revision: https://reviews.llvm.org/D44102

llvm-svn: 326908