[llvm] [LV][NFC] Change undef to poison in most tests (PR #163525)

[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/test/Transforms/LoopVectorize/12-12-11-if-conv.ll llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll llvm/test/Transforms/LoopVectorize/AArch64/pr33053.ll llvm/test/Transforms/LoopVectorize/AArch64/pr36032.ll llvm/test/Transforms/LoopVectorize/AArch64/sve-interleaved-accesses.ll llvm/test/Transforms/LoopVectorize/ARM/arm-ieee-vectorize.ll llvm/test/Transforms/LoopVectorize/ARM/mve-known-trip-count.ll llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll llvm/test/Transforms/LoopVectorize/X86/avx1.ll llvm/test/Transforms/LoopVectorize/X86/consecutive-ptr-cg-bug.ll llvm/test/Transforms/LoopVectorize/X86/conversion-cost.ll llvm/test/Transforms/LoopVectorize/X86/cost-model-assert.ll llvm/test/Transforms/LoopVectorize/X86/fp80-widest-type.ll llvm/test/Transforms/LoopVectorize/X86/interleaved-accesses-large-gap.ll llvm/test/Transforms/LoopVectorize/X86/pr39160.ll llvm/test/Transforms/LoopVectorize/X86/rauw-bug.ll llvm/test/Transforms/LoopVectorize/X86/runtime-limit.ll llvm/test/Transforms/LoopVectorize/X86/unroll-pm.ll llvm/test/Transforms/LoopVectorize/X86/x86_fp80-interleaved-access.ll llvm/test/Transforms/LoopVectorize/bsd_regex.ll llvm/test/Transforms/LoopVectorize/demanded-bits-of-pointer-instruction.ll llvm/test/Transforms/LoopVectorize/i8-induction.ll llvm/test/Transforms/LoopVectorize/if-conversion-nest.ll llvm/test/Transforms/LoopVectorize/if-conversion.ll llvm/test/Transforms/LoopVectorize/if-pred-stores.ll llvm/test/Transforms/LoopVectorize/incorrect-dom-info.ll llvm/test/Transforms/LoopVectorize/interleaved-accesses-uniform-load.ll llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll llvm/test/Transforms/LoopVectorize/invariant-store-vectorization.ll llvm/test/Transforms/LoopVectorize/iv_outside_user.ll llvm/test/Transforms/LoopVectorize/lcssa-crashes.ll llvm/test/Transforms/LoopVectorize/memdep.ll llvm/test/Transforms/LoopVectorize/middle-block-dbg.ll llvm/test/Transforms/LoopVectorize/multi-use-reduction-bug.ll llvm/test/Transforms/LoopVectorize/nsw-crash.ll llvm/test/Transforms/LoopVectorize/optsize.ll llvm/test/Transforms/LoopVectorize/partial-lcssa.ll llvm/test/Transforms/LoopVectorize/pr28541.ll llvm/test/Transforms/LoopVectorize/pr32859.ll llvm/test/Transforms/LoopVectorize/pr36311.ll llvm/test/Transforms/LoopVectorize/reduction-inloop.ll llvm/test/Transforms/LoopVectorize/reduction-ptr.ll llvm/test/Transforms/LoopVectorize/reduction-small-size.ll llvm/test/Transforms/LoopVectorize/reverse_iter.ll llvm/test/Transforms/LoopVectorize/runtime-check.ll llvm/test/Transforms/LoopVectorize/runtime-drop-crash.ll llvm/test/Transforms/LoopVectorize/scalable-first-order-recurrence.ll llvm/test/Transforms/LoopVectorize/scev-exitlim-crash.ll llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll llvm/test/Transforms/LoopVectorize/undef-inst-bug.ll llvm/test/Transforms/LoopVectorize/uniform-blend.ll llvm/test/Transforms/LoopVectorize/value-ptr-bug.ll llvm/test/Transforms/LoopVectorize/vector-to-scalar-cast.ll llvm/test/Transforms/LoopVectorize/write-only.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/Transforms/LoopVectorize/if-conversion.ll
 - llvm/test/Transforms/LoopVectorize/lcssa-crashes.ll
 - llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll
 - llvm/test/Transforms/LoopVectorize/undef-inst-bug.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/163525