| Issue |
126406
|
| Summary |
`assume`ing the result isn't setting the `nsw` flag on `add`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
scottmcm
|
Original Rust example: <https://rust.godbolt.org/z/xze3vEx8E>
```rust
pub unsafe fn extend_packed_unchecked(a: Layout, b: Layout) -> usize {
a.extend_packed(b).unwrap_unchecked().size()
}
```
Actual output (-) and what I'd like to get instead (+):
```diff
define noundef i64 @extend_packed_unchecked(i64 noundef range(i64 1, -9223372036854775807) %0, i64 noundef %1, i64 noundef range(i64 1, -9223372036854775807) %b.0, i64 noundef %b.1) unnamed_addr {
start:
- %new_size = add nuw i64 %b.1, %1
+ %new_size = add nuw nsw i64 %b.1, %1
%_11 = sub nuw i64 -9223372036854775808, %0
%_10 = icmp ule i64 %new_size, %_11
tail call void @llvm.assume(i1 %_10)
ret i64 %new_size
}
```
Note that `%_11 sgt -1`, thanks to the range attribute on the `%0` parameter.
Alive proof that this is allowed: <https://alive2.llvm.org/ce/z/Dn2P8R>
Repro that more `opt` on trunk doesn't do it: <https://llvm.godbolt.org/z/Kr8n37s41>
---
Oh, turns out the simpler case of just
```llvm
define noundef i64 @demo_b(i64 noundef %1, i64 noundef %b.1) unnamed_addr {
start:
%new_size = add nuw i64 %b.1, %1
%_10 = icmp ule i64 %new_size, 9223372036854775807
tail call void @llvm.assume(i1 %_10)
ret i64 %new_size
}
```
doesn't add the `nsw` either.
And that'd be allowed too: <https://alive2.llvm.org/ce/z/PeC7No>
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