Reverting because mis-compiles:
- https://github.com/llvm/llvm-project/pull/131837
- https://github.com/llvm/llvm-project/pull/146320
- https://github.com/llvm/llvm-project/pull/146337

None of these implicitly generate UNDEF/POISON

This is alternative to #145965 that allows RegisterSDNode to be handled
without making a special case.

This PR resolves https://github.com/llvm/llvm-project/issues/144513

The modification include five pattern :
1.vselect Cond, 0, 0 → 0
2.vselect Cond, -1, 0 → bitcast Cond
3.vselect Cond, -1, x → or Cond, x
4.vselect Cond, x, 0 → and Cond, x
5.vselect Cond, 000..., X -> andn Cond, X

1-4 have been migrated to DAGCombine. 5 still in x86 code.

The reason is that you cannot use the andn instruction directly in
DAGCombine, you can only use and+xor, which will introduce optimization
order issues. For example, in the x86 backend, select Cond, 0, x →
(~Cond) & x, the backend will first check whether the cond node of
(~Cond) is a setcc node. If so, it will modify the comparison operator
of the condition.So the x86 backend cannot complete the optimization of
andn.In short, I think it is a better choice to keep the pattern of
vselect Cond, 000..., X instead of and+xor in combineDAG.

For commit, the first is code changes and x86 test(note 1), the second
is tests in other backend(node 2).

---------

Co-authored-by: Simon Pilgrim <llvm-dev@redking.me.uk>

Always try to fold freeze(op(....)) -> op(freeze(),freeze(),freeze(),...).

This patch proposes we drop the opt-in limit for opcodes that are allowed to push a freeze through the op to freeze all its operands, through the tree towards the roots.

I'm struggling to find a strong reason for this limit apart from the DAG freeze handling being immature for so long - as we've improved coverage in canCreateUndefOrPoison/isGuaranteedNotToBeUndefOrPoison it looks like the regressions are not as severe.

Hopefully this will help some of the regression issues in #143102 etc.

After 901e1390c9778a191256335d37802bc631c2d183 (#127770), the DAG
combine would transform `fma(x, 0.0, 1.0)` into `1.0` if
`-fp-contract=fast` was enabled, in addition to when 'x' is marked
nnan/ninf.

It's only valid in the latter case, not the former, so delete the extra
condition.

Ensure we load BOTH scalars, inserted into different positions into separate vectors with the freeze(poison) base

Noticed while triaging regressions in #145939

CTTZ/CTLZ_ZERO_UNDEF nodes can only create poison if the source value is zero - so check with isKnownNeverZero

Pulled out of #146361 and reapplied now that #146490 has landed.