[ConstantRange] Remove costly udivrem from ConstantRange::truncate

[ConstantRange] Remove costly udivrem from ConstantRange::truncate

Truncate currently uses a udivrem call which is going to be slow particularly for larger than 64-bit widths.

As far as I can tell all we were trying to do was modulo LowerDiv by (MaxValue+1) and make sure whatever value was effectively subtracted from LowerDiv was also subtracted from UpperDiv.

This patch recognizes that MaxValue+1 is a power of 2 so we can just use a bitwise AND to accomplish a modulo operation or isolate the upper bits.

Differential Revision: https://reviews.llvm.org/D32672

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304733 91177308-0d34-0410-b5e6-96231b3b80d8