[llvm] AMDGPU: Replace undef phi inputs with poison in tests (PR #130267)

[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)' 21610e3ecc8bc727f99047e544186b35b1291bcd 167d79b0fa6ed7f087a9f4a3c16a0d763b7e5a3d llvm/test/CodeGen/AMDGPU/GlobalISel/divergent-control-flow.ll llvm/test/CodeGen/AMDGPU/amdgpu-codegenprepare-break-large-phis.ll llvm/test/CodeGen/AMDGPU/amdpal_scratch_mergedshader.ll llvm/test/CodeGen/AMDGPU/branch-relaxation.ll llvm/test/CodeGen/AMDGPU/bug-deadlanes.ll llvm/test/CodeGen/AMDGPU/coalescer_distribute.ll llvm/test/CodeGen/AMDGPU/combine-add-zext-xor.ll llvm/test/CodeGen/AMDGPU/cse-phi-incoming-val.ll llvm/test/CodeGen/AMDGPU/dagcomb-shuffle-vecextend-non2.ll llvm/test/CodeGen/AMDGPU/dagcombine-fma-crash.ll llvm/test/CodeGen/AMDGPU/divergent-branch-uniform-condition.ll llvm/test/CodeGen/AMDGPU/fold-fabs.ll llvm/test/CodeGen/AMDGPU/i1-copy-phi.ll llvm/test/CodeGen/AMDGPU/implicit-def-muse.ll llvm/test/CodeGen/AMDGPU/inline-asm.ll llvm/test/CodeGen/AMDGPU/llvm.amdgcn.ds.ordered.swap.ll llvm/test/CodeGen/AMDGPU/madmk.ll llvm/test/CodeGen/AMDGPU/mdt-preserving-crash.ll llvm/test/CodeGen/AMDGPU/move-to-valu-worklist.ll llvm/test/CodeGen/AMDGPU/multilevel-break.ll llvm/test/CodeGen/AMDGPU/nested-loop-conditions.ll llvm/test/CodeGen/AMDGPU/rewrite-undef-for-phi.ll llvm/test/CodeGen/AMDGPU/schedule-vs-if-nested-loop-failure.ll llvm/test/CodeGen/AMDGPU/sdwa-peephole.ll llvm/test/CodeGen/AMDGPU/select-undef.ll llvm/test/CodeGen/AMDGPU/si-spill-cf.ll llvm/test/CodeGen/AMDGPU/simplifydemandedbits-recursion.ll llvm/test/CodeGen/AMDGPU/skip-if-dead.ll llvm/test/CodeGen/AMDGPU/subreg-coalescer-crash.ll llvm/test/CodeGen/AMDGPU/switch-default-block-unreachable.ll llvm/test/CodeGen/AMDGPU/tuple-allocation-failure.ll llvm/test/CodeGen/AMDGPU/uniform-phi-with-undef.ll llvm/test/CodeGen/AMDGPU/unigine-liveness-crash.ll llvm/test/CodeGen/AMDGPU/vgpr-liverange-ir.ll llvm/test/CodeGen/AMDGPU/wave32.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/CodeGen/AMDGPU/rewrite-undef-for-phi.ll
 - llvm/test/CodeGen/AMDGPU/select-undef.ll
 - llvm/test/CodeGen/AMDGPU/uniform-phi-with-undef.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/130267