[CodeGen][SelectionDAG] More efficient code for X % C == 0 (SREM case)

[CodeGen][SelectionDAG] More efficient code for X % C == 0 (SREM case)

Summary:
This implements an optimization described in Hacker's Delight 10-17:
when `C` is constant, the result of `X % C == 0` can be computed
more cheaply without actually calculating the remainder.
The motivation is discussed here: https://bugs.llvm.org/show_bug.cgi?id=35479.

One huge caveat: this signed case is only valid for positive divisors.

While we can freely negate negative divisors, we can't negate `INT_MIN`,
so for now if `INT_MIN` is encountered, we bailout.
As a follow-up, it should be possible to handle that more gracefully
via extra `and`+`setcc`+`select`.

This passes llvm's test-suite, and from cursory(!) cross-examination
the folds (the assembly) match those of GCC, and manual checking via alive
did not reveal any issues (other than the `INT_MIN` case)

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

Reviewed By: RKSimon, xbolva00

Subscribers: xbolva00, thakis, javed.absar, hiraditya, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65366

llvm-svn: 368702