[llvm] [SLP]Represent SLP graph as a tree (PR #126771)

[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)' 404f94ac7d8c368fba8ad1f97512c26efd5ec965 e157634b62cd4a735d27514854534ee9587f4699 llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp llvm/test/Transforms/SLPVectorizer/AArch64/horizontal.ll llvm/test/Transforms/SLPVectorizer/AArch64/remarks.ll llvm/test/Transforms/SLPVectorizer/AArch64/reorder-fmuladd-crash.ll llvm/test/Transforms/SLPVectorizer/AArch64/vectorize-free-extracts-inserts.ll llvm/test/Transforms/SLPVectorizer/RISCV/remarks_cmp_sel_min_max.ll llvm/test/Transforms/SLPVectorizer/RISCV/small-phi-tree.ll llvm/test/Transforms/SLPVectorizer/SystemZ/SLP-cmp-cost-query.ll llvm/test/Transforms/SLPVectorizer/X86/cmp-after-intrinsic-call-minbitwidth.ll llvm/test/Transforms/SLPVectorizer/X86/crash_7zip.ll llvm/test/Transforms/SLPVectorizer/X86/delayed-gather-emission.ll llvm/test/Transforms/SLPVectorizer/X86/external-reduced-value-vectorized.ll llvm/test/Transforms/SLPVectorizer/X86/extractelemets-extended-by-poison.ll llvm/test/Transforms/SLPVectorizer/X86/full-matched-bv-with-subvectors.ll llvm/test/Transforms/SLPVectorizer/X86/gather-node-same-as-vect-but-order.ll llvm/test/Transforms/SLPVectorizer/X86/gathered-delayed-nodes-with-reused-user.ll llvm/test/Transforms/SLPVectorizer/X86/geps-non-pow-2.ll llvm/test/Transforms/SLPVectorizer/X86/matching-gather-nodes-phi-users.ll llvm/test/Transforms/SLPVectorizer/X86/minbitwidth-icmp-to-trunc.ll llvm/test/Transforms/SLPVectorizer/X86/minbw-node-used-twice.ll llvm/test/Transforms/SLPVectorizer/X86/perfect-matched-reused-bv.ll llvm/test/Transforms/SLPVectorizer/X86/phi-node-with-cycle.ll llvm/test/Transforms/SLPVectorizer/X86/phi-nodes-as-operand-reorder.ll llvm/test/Transforms/SLPVectorizer/X86/reused-mask-with-poison-index.ll llvm/test/Transforms/SLPVectorizer/X86/shrink_after_reorder.ll llvm/test/Transforms/SLPVectorizer/X86/slp-schedule-use-order.ll llvm/test/Transforms/SLPVectorizer/X86/subvector-minbitwidth-unsigned-value.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/Transforms/SLPVectorizer/X86/crash_7zip.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/126771