[llvm] [AArch64][SelectionDAG] Add CodeGen support for FEAT_CPA (PR #105669)

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github-actions[bot] wrote:

<!--LLVM CODE FORMAT COMMENT: {undef deprecator}-->


:warning: undef deprecator found issues in your code. :warning:

<details>
<summary>
You can test this locally with the following command:
</summary>

``````````bash
git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9_-]|UndefValue::get)' 57466db7a459ce285f053ecac3c309f49f2cce6a eebe5386961842be7554ba207f6608dee8d91e05 llvm/test/CodeGen/AArch64/cpa-globalisel.ll llvm/test/CodeGen/AArch64/cpa-selectiondag.ll llvm/include/llvm/CodeGen/ISDOpcodes.h llvm/include/llvm/CodeGen/SelectionDAG.h llvm/include/llvm/Target/TargetMachine.h llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp llvm/lib/Target/AArch64/AArch64TargetMachine.cpp llvm/lib/Target/AArch64/AArch64TargetMachine.h llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
``````````

</details>


The following files introduce new uses of undef:
 - llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

[Undef](https://llvm.org/docs/LangRef.html#undefined-values) is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields `undef`. You should use `poison` values for placeholders instead.

In tests, avoid using `undef` and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:
```llvm
define void @fn() {
  ...
  br i1 undef, ...
}
```

Please use the following instead:
```llvm
define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}
```

Please refer to the [Undefined Behavior Manual](https://llvm.org/docs/UndefinedBehavior.html) for more information.



https://github.com/llvm/llvm-project/pull/105669