[llvm] [GVN] MemorySSA for GVN: eliminate redundant loads via MemorySSA (PR #152859)

[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/include/llvm/Transforms/Scalar/GVN.h llvm/lib/Transforms/Scalar/GVN.cpp llvm/test/Analysis/TypeBasedAliasAnalysis/gvn-nonlocal-type-mismatch.ll llvm/test/Transforms/GVN/PRE/load-metadata.ll llvm/test/Transforms/GVN/PRE/lpre-call-wrap.ll llvm/test/Transforms/GVN/PRE/phi-translate-2.ll llvm/test/Transforms/GVN/PRE/phi-translate-add.ll llvm/test/Transforms/GVN/PRE/phi-translate.ll llvm/test/Transforms/GVN/PRE/pre-after-rle.ll llvm/test/Transforms/GVN/PRE/pre-aliasning-path.ll llvm/test/Transforms/GVN/PRE/pre-load-dbg.ll llvm/test/Transforms/GVN/PRE/pre-load-guards.ll llvm/test/Transforms/GVN/PRE/pre-load-implicit-cf-updates.ll llvm/test/Transforms/GVN/PRE/pre-load.ll llvm/test/Transforms/GVN/PRE/pre-single-pred.ll llvm/test/Transforms/GVN/PRE/preserve-tbaa.ll llvm/test/Transforms/GVN/PRE/rle-addrspace-cast.ll llvm/test/Transforms/GVN/PRE/rle-semidominated.ll llvm/test/Transforms/GVN/PRE/rle.ll llvm/test/Transforms/GVN/nonescaping.ll llvm/test/Transforms/GVN/pr14166.ll llvm/test/Transforms/GVN/readattrs.ll llvm/test/Transforms/GVN/setjmp.ll llvm/test/Transforms/GVN/tbaa.ll llvm/test/Transforms/GVN/vscale.ll
``````````

</details>


The following files introduce new uses of undef:
 - llvm/test/Transforms/GVN/PRE/pre-load-dbg.ll
 - llvm/test/Transforms/GVN/vscale.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/152859