[llvm] [IndVarSimplify] Don't perform LFTR only to convert the predicate (PR #126086)

[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)' 88b1d16c4a040cc3d919be13f0baf44f30a5aa13 995d1e152b90801bf7dce924cad3ef393bc91bdc llvm/lib/Transforms/Scalar/IndVarSimplify.cpp llvm/test/Transforms/IndVarSimplify/2011-11-01-lftrptr.ll llvm/test/Transforms/IndVarSimplify/AArch64/widen-loop-comp.ll llvm/test/Transforms/IndVarSimplify/X86/eliminate-trunc.ll llvm/test/Transforms/IndVarSimplify/X86/inner-loop-by-latch-cond.ll llvm/test/Transforms/IndVarSimplify/X86/iv-widen.ll llvm/test/Transforms/IndVarSimplify/X86/loop-invariant-conditions.ll llvm/test/Transforms/IndVarSimplify/X86/pr35406.ll llvm/test/Transforms/IndVarSimplify/X86/pr59615.ll llvm/test/Transforms/IndVarSimplify/X86/widening-vs-and-elimination.ll llvm/test/Transforms/IndVarSimplify/ada-loops.ll llvm/test/Transforms/IndVarSimplify/ashr-expansion.ll llvm/test/Transforms/IndVarSimplify/canonicalize-cmp.ll llvm/test/Transforms/IndVarSimplify/deterministic-sign.ll llvm/test/Transforms/IndVarSimplify/drop-exact.ll llvm/test/Transforms/IndVarSimplify/elim-extend.ll llvm/test/Transforms/IndVarSimplify/eliminate-comparison.ll llvm/test/Transforms/IndVarSimplify/finite-exit-comparisons.ll llvm/test/Transforms/IndVarSimplify/full_widening.ll llvm/test/Transforms/IndVarSimplify/iv-ext-samesign.ll llvm/test/Transforms/IndVarSimplify/iv-sext.ll llvm/test/Transforms/IndVarSimplify/iv-widen-elim-ext.ll llvm/test/Transforms/IndVarSimplify/lftr-address-space-pointers.ll llvm/test/Transforms/IndVarSimplify/lftr-dead-ivs.ll llvm/test/Transforms/IndVarSimplify/lftr-multi-exit.ll llvm/test/Transforms/IndVarSimplify/lftr-pr20680.ll llvm/test/Transforms/IndVarSimplify/lftr-pr31181.ll llvm/test/Transforms/IndVarSimplify/lftr-reuse.ll llvm/test/Transforms/IndVarSimplify/lftr.ll llvm/test/Transforms/IndVarSimplify/no-iv-rewrite.ll llvm/test/Transforms/IndVarSimplify/post-inc-range.ll llvm/test/Transforms/IndVarSimplify/pr79861.ll llvm/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-values-phi.ll llvm/test/Transforms/IndVarSimplify/rlev-add-me.ll llvm/test/Transforms/IndVarSimplify/trip-count-expansion-loop-guard-preserve-nsw.ll llvm/test/Transforms/IndVarSimplify/ult-sub-to-eq.ll llvm/test/Transforms/IndVarSimplify/widen-nonnegative.ll
``````````

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The following files introduce new uses of undef:
 - llvm/test/Transforms/IndVarSimplify/rewrite-loop-exit-values-phi.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/126086