[llvm] [Hexagon] Add MachineUnroller pass (PR #177197)

[via llvm-commits]

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)' 'HEAD~1' HEAD llvm/include/llvm/CodeGen/MachineUnroller.h llvm/lib/CodeGen/MachineUnroller.cpp llvm/lib/CodeGen/MachineUnrollerPass.cpp llvm/lib/Target/Hexagon/HexagonMachineUnroller.cpp llvm/lib/Target/Hexagon/HexagonMachineUnroller.h llvm/test/CodeGen/Hexagon/dbg-instr-machunroll.ll llvm/test/CodeGen/Hexagon/dbg-label-machunroll.ll llvm/test/CodeGen/Hexagon/machine-unroller-remarks.ll llvm/test/CodeGen/Hexagon/miunroll-adjust-resmii.ll llvm/test/CodeGen/Hexagon/miunroll-optimize-memrefs1.ll llvm/test/CodeGen/Hexagon/miunroll-selfdependency.ll llvm/test/CodeGen/Hexagon/miunroll-selfdependency2.ll llvm/test/CodeGen/Hexagon/miunroll-update-memoperands.ll llvm/test/CodeGen/Hexagon/miunroll-valign.ll llvm/test/CodeGen/Hexagon/miunroll.ll llvm/include/llvm/CodeGen/Passes.h llvm/include/llvm/CodeGen/TargetPassConfig.h llvm/include/llvm/InitializePasses.h llvm/lib/CodeGen/CodeGen.cpp llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/CodeGen/Hexagon/miunroll-update-memoperands.ll
 - llvm/test/CodeGen/Hexagon/miunroll-valign.ll

[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/177197