[llvm] SCEV: teach isImpliedViaOperations about samesign (PR #124270)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

Hi,

I bisected (what I think is) a miscompile back to this patch.

Reduced indvars reproducer:
```opt -passes="indvars" bbi-103889.ll -S -o -```

The problem is that with this patch it changes the input
```%add = add i16 %0, 2```
to
```%add = add nuw nsw i16 %1, 2```
but we're iterating from 32760 to 32780, doing "ult" comparisons, so we do get signed wrap around in the add.

[bbi-103889.ll.gz](https://github.com/user-attachments/files/18730249/bbi-103889.ll.gz)




https://github.com/llvm/llvm-project/pull/124270