| Issue |
89390
|
| Summary |
VectorCombine transform leading to srem by poison
|
| Labels |
miscompilation,
llvm:instcombine
|
| Assignees |
|
| Reporter |
regehr
|
https://alive2.llvm.org/ce/z/HRAkAK
this:
```llvm
define <4 x i32> @f(<4 x i32> %0, <4 x i32> %1) {
%3 = srem <4 x i32> %1, %0
%4 = srem <4 x i32> <i32 1, i32 1, i32 1, i32 1>, %0
%5 = shufflevector <4 x i32> %3, <4 x i32> %4, <4 x i32> <i32 0, i32 poison, i32 6, i32 3>
ret <4 x i32> %5
}
```
is getting vector-combined to this:
```llvm
define <4 x i32> @f(<4 x i32> %0, <4 x i32> %1) {
%3 = shufflevector <4 x i32> %1, <4 x i32> <i32 1, i32 1, i32 1, i32 1>, <4 x i32> <i32 0, i32 poison, i32 6, i32 3>
%4 = shufflevector <4 x i32> %0, <4 x i32> poison, <4 x i32> <i32 0, i32 poison, i32 2, i32 3>
%5 = srem <4 x i32> %3, %4
ret <4 x i32> %5
}
```
but that poison in lane 1 is now problematic, this gives us full UB when it hits the srem
cc @nunoplopes @hatsunespica
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