| Issue |
174046
|
| Summary |
[VectorCombine] `calarizeExtExtract` miscompiles i64 elements due to `(1ull << 64)`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
cardigan1008
|
`VectorCombine::scalarizeExtExtract` computes the element mask as:
```cpp
EltBitMask = (1ull << SrcEltSizeInBits) - 1;
```
When `SrcEltSizeInBits == 64` (e.g. `<2 x i64>`), this is C++ UB and can produce `EltBitMask = 0`. As a result, VectorCombine may replace an `extractelement` with constant `0`, causing miscompilation.
Alive2 proof: https://alive2.llvm.org/ce/z/5-Dyc4
Exposed from https://github.com/llvm/llvm-project/commit/994a6a39e13dcc335247a127a5da05905d1ac541, cc @uyoyo0
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