[Codegen][SelectionDAG] X u% C == 0 fold: non-splat vector improvements

[Codegen][SelectionDAG] X u% C == 0 fold: non-splat vector improvements

Summary:
Four things here:
1. Generalize the fold to handle non-splat divisors. Reasonably trivial.
2. Unban power-of-two divisors. I don't see any reason why they should
   be illegal.
   * There is no ban in Hacker's Delight
   * I think the ban came from the same bug that caused the miscompile
      in the base patch - in `floor((2^W - 1) / D)` we were dividing by
      `D0` instead of `D`, and we **were** ensuring that `D0` is not `1`,
      which made sense.
3. Unban `1` divisors. I no longer believe Hacker's Delight actually says
   that the fold is invalid for `D = 0`. Further considerations:
   * We know that
     * `(X u% 1) == 0`  can be constant-folded to `1`,
     * `(X u% 1) != 0`  can be constant-folded to `0`,
   *  Also, we know that
     * `X u<= -1` can be constant-folded to `1`,
     * `X u>  -1` can be constant-folded to `0`,
   * https://godbolt.org/z/7jnZJX https://rise4fun.com/Alive/oF6p
   * We know will end up with the following:
       `(setule/setugt (rotr (mul N, P), K), Q)`
   * Therefore, for given new DAG nodes and comparison predicates
     (`ule`/`ugt`), we will still produce the correct answer if:
     `Q` is a all-ones constant; and both `P` and `K` are *anything*
     other than `undef`.
   * The fold will indeed produce `Q = all-ones`.
4. Try to re-splat the `P` and `K` vectors - we don't care about
   their values for the lanes where divisor was `1`.

Reviewers: RKSimon, hermord, craig.topper, spatel, xbolva00

Reviewed By: RKSimon

Subscribers: hiraditya, javed.absar, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63963

llvm-svn: 366637