| Issue |
174041
|
| Summary |
[SLP] Miscompile when vectorizing `xor x, 0` with and `y, -1`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
cardigan1008
|
In https://github.com/llvm/llvm-project/commit/1f82553e385f449efee92da3dca43facb4a1ee66, SLPVectorizer may incorrectly vectorize a pair of identity operations `xor x, 0` and and `y, -1` into a single vector and instruction. Because the identity constants differ (0 vs -1), SLP forms a mixed constant vector <0, -1> and emits:
```llvm
and <2 x i32> <x, y>, <0, -1>
```
This forces the first lane to `0` instead of `x`. When the original code stores results separately, this changes observable memory behavior (e.g. with `y = poison`).
Alive2 proof: https://alive2.llvm.org/ce/z/CtTFRH
Exposed from https://github.com/llvm/llvm-project/commit/1f82553e385f449efee92da3dca43facb4a1ee66, cc @alexey-bataev
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