[llvm] [GlobalISel] An optimizing MIR builder (PR #132282)

[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)' 99b1a2ac078fe52300d270b3e77ddbababa8f951 bee977e130ca598d481f236e33370c70ed77ac8a llvm/include/llvm/CodeGen/GlobalISel/OptMIRBuilder.h llvm/lib/CodeGen/GlobalISel/OptMIRBuilder.cpp llvm/include/llvm/CodeGen/GlobalISel/Utils.h llvm/lib/CodeGen/GlobalISel/CSEMIRBuilder.cpp llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp llvm/lib/CodeGen/GlobalISel/Utils.cpp llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerCombiner.cpp llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll llvm/test/CodeGen/AArch64/GlobalISel/combine-udiv.ll llvm/test/CodeGen/AArch64/arm64-neon-mul-div-cte.ll llvm/test/CodeGen/AArch64/fsh.ll llvm/test/CodeGen/AArch64/funnel-shift.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/include/llvm/CodeGen/GlobalISel/OptMIRBuilder.h

[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/132282