Need to check if the non-schedulable phi parent node has unique
operands, if the incoming node has copyables, and the node is
commutative. Otherwise, there might be issues with the correct
calculation of the dependencies.

Fixes #168589

The problem with the many def-use chain problems in SLP vectorizer are
related to the fact that some nodes reuse the same instruction as
insertion point. Insertion point is not the instruction, but the place
between instructions. To set it correctly, better to generate pseudo
instruction immediately after the last instruction, and use it as
insertion point. It resolves the issues in most cases.

Fixes #168512 #168576

Given a set of pointers, check if they can be rearranged as follows (%s is a constant):
%b + 0 * %s + 0
%b + 0 * %s + 1
%b + 0 * %s + 2
...
%b + 0 * %s + w

%b + 1 * %s + 0
%b + 1 * %s + 1
%b + 1 * %s + 2
...
%b + 1 * %s + w
...

If the pointers can be rearanged in the above pattern, it means that the
memory can be accessed with a strided loads of width `w` and stride `%s`.

- Remove file local functions out of `llvm` or anonymous namespace and
make them static.
- Use namespace qualifier to define `BoUpSLP` class and several template
specializations.

- Split from #165532. This is a step toward a unified interface for
masked/gather-scatter/strided/expand-compress cost modeling.
- Replace the ad-hoc parameter list with a single attributes object.

API change:
```
- InstructionCost getMaskedMemoryOpCost(Opcode, Src, Alignment,
-                                       AddressSpace, CostKind);

+ InstructionCost getMaskedMemoryOpCost(MemIntrinsicCostAttributes,
+                                       CostKind);
```
Notes:
- NFCI intended: callers populate MemIntrinsicCostAttributes with the
same information as before.
- Follow-up: migrate gather/scatter, strided, and expand/compress cost
queries to the same attributes-based entry point.

The compiler should not consider split vectorize nodes, when checking
for non-schedulable PHI-based parent nodes. Only pure PHI nodes must be
  considered, they only can be considered as explicit users, split nodes
  are not.

Fixes #168268

Need to check if the non-copyable element is an instruction before actually
trying to check its NSW attribute.

This reverts commit ddf5bb0a2e2d2dd77bce66173387d62ab7174d9f to fix
buildbots  https://lab.llvm.org/buildbot/#/builders/11/builds/28083.

Need to check if the non-copyable element is an instruction before actually
trying to check its NSW attribute.