[llvm] Revert "Redesign Straight-Line Strength Reduction (SLSR) (#162930)" (PR #169546)

[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/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp llvm/test/CodeGen/AMDGPU/agpr-copy-no-free-registers.ll llvm/test/CodeGen/AMDGPU/dagcombine-reassociate-bug.ll llvm/test/CodeGen/AMDGPU/idot2.ll llvm/test/CodeGen/AMDGPU/idot4s.ll llvm/test/CodeGen/AMDGPU/idot8u.ll llvm/test/CodeGen/AMDGPU/promote-constOffset-to-imm.ll llvm/test/CodeGen/AMDGPU/splitkit-getsubrangeformask.ll llvm/test/CodeGen/AMDGPU/waitcnt-vscnt.ll llvm/test/Transforms/StraightLineStrengthReduce/AMDGPU/pr23975.ll llvm/test/Transforms/StraightLineStrengthReduce/AMDGPU/reassociate-geps-and-slsr-addrspace.ll llvm/test/Transforms/StraightLineStrengthReduce/slsr-add.ll llvm/test/Transforms/StraightLineStrengthReduce/slsr-gep.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/169546