Make ValueTracking directly call the KnownBits shift helpers, which
provides more precise results.
Unfortunately, ValueTracking has a special case where sometimes we
determine non-zero shift amounts using isKnownNonZero(). I have my
doubts about the usefulness of that special-case (it is only tested
in a single unit test), but I've reproduced the special-case via an
extra parameter to the KnownBits methods.
Differential Revision: https://reviews.llvm.org/D151816
This patch adds support for implication inference logic for the
following pattern:
```
lhs < (y >> z) <= y, y <= rhs --> lhs < rhs
```
We should be able to use the fact that value shifted to right is
not greater than the original value (provided it is non-negative).
Differential Revision: https://reviews.llvm.org/D116150
Reviewed-By: apilipenko
