Fehr Mathieu 8b67f36258 [mlir] [arith] Fix ceildivsi lowering in arith-expand (#133774) ...

This fixes the current lowering of `arith.ceildivsi` in the arith-expand
pass, which was previously incorrect. The new version is based on the
lowering of `arith.floordivsi`, and will not introduce new undefined
behavior or poison during the lowering. It also replaces one division
with a multiplication.

The previous lowering of `ceildivsi(n, m)` was the following:
```
x = (m > 0) ? -1 : 1
(n*m>0) ? ((n+x) / m) + 1 : - (-n / m)
```

This caused two problems:
* In the case where `n` is INT_MIN and `m` is positive, the result would
be poison instead of an actual value
* In the case where `n` is INT_MAX and `m` is `-1`, this would trigger
undefined behavior, while the original code wouldn't. This is because
`n+x` would be equal to `INT_MIN` (`INT_MAX + 1`), so the `(n+x) / m`
division would overflow and trigger UB.

2025-04-02 17:26:58 +01:00

16 KiB

Raw Blame History

View Raw