Re-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 causing performance regressions.  Re-landing
because we've determined that these regressions were noise.

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328096 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed