This patch allows urem by a constant to be expanded more efficiently to
avoid the need for expensive udiv instructions. This is part of the
resolution to issue #118090

In the pre-legalizer combiner, there exists a bug with UseVectorTruncate
match-apply optimization. When the destinations' types do not match the
vector element type of the G_UNMERGE_VALUES instruction, the resulting
collapsed truncate does not preserve original functional behavior. This
commit introduces a simple type check to ensure that the destination
types match the vector element type.

Fixes issue: https://github.com/llvm/llvm-project/issues/139752

When G_SHUFFLE_VECTOR has only 1 element then it is possible the vector
is decayed into a scalar.

As shown in https://alive2.llvm.org/ce/z/PVwcTL we need to clear the nsw
flags too when converting a sub to a add if the constant is INT_MIN.

Fixes #137254

This patch dismantles G_SHUFFLE_VECTOR before lowering. The original
lowering would emit extract vector element ops. We found that by using
unmerged values the build vector op combine could find ways to fold.

Only enabled on AMDGPU.

This resolves #123631

- rename `GISelKnownBits` to `GISelValueTracking` to analyze more than
just `KnownBits` in the future

We need to check `G_CTLZ` because the combine uses `G_CTLZ` to get log
base 2,
and it is not always legal for on a target.

Fixes SWDEV-512440.