[llvm] [Scalar] Dedicated pass for identifying redundant operations on packed bytes (PR #146364)

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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)' 'HEAD~1' HEAD llvm/include/llvm/Transforms/Scalar/PackedIntegerCombinePass.h llvm/lib/Transforms/Scalar/PackedIntegerCombinePass.cpp llvm/test/Transforms/PackedIntegerCombine/instructions.ll llvm/test/Transforms/PackedIntegerCombine/int2int.ll llvm/test/Transforms/PackedIntegerCombine/int2vec.ll llvm/test/Transforms/PackedIntegerCombine/vec2int.ll llvm/test/Transforms/PackedIntegerCombine/vec2vec.ll llvm/include/llvm/InitializePasses.h llvm/include/llvm/Transforms/Scalar.h llvm/lib/Passes/PassBuilder.cpp llvm/lib/Passes/PassBuilderPipelines.cpp llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp llvm/lib/Transforms/Scalar/Scalar.cpp llvm/test/CodeGen/AMDGPU/combine-vload-extract.ll llvm/test/CodeGen/AMDGPU/llc-pipeline.ll llvm/test/CodeGen/AMDGPU/sdwa-peephole.ll llvm/test/CodeGen/AMDGPU/splitkit-getsubrangeformask.ll llvm/test/Other/new-pm-defaults.ll llvm/test/Other/new-pm-thinlto-postlink-defaults.ll llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll llvm/test/Other/new-pm-thinlto-prelink-defaults.ll llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/CodeGen/AMDGPU/splitkit-getsubrangeformask.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/146364