[llvm] SimplifyIndVar: teach widenLoopCompare about samesign (PR #125764)

[Nikita Popov via llvm-commits]

nikic wrote:

> > I'm also wondering why the nested loops are needed for these tests. Shouldn't it be possible to show the same behavior without them and simplify the tests?
> 
> For this patch itself, yes. I merely re-used the tests that Yingwei had provided from the original regression: for that, I'm not able to reproduce the behavior without nested loops.

Would it make sense to only keep the original test case once as motivation, but test the details of the change itself with simple tests?

https://github.com/llvm/llvm-project/pull/125764