[llvm] [InstCombine] Do not keep samesign when speculatively executing icmps (PR #127007)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> > > As an alternative, we can pass `UseInstrInfo=false` to `simplifyICmpInst`.
> > 
> > 
> > Is the underlying issue `simplifyICmpInst` though?
> 
> Yeah. If `UseInstrInfo` is false, we cannot use poison-generating flags.

Very sorry about this, but I'm still having trouble understanding which exact `UseInstrInfo` check would resolve the problem. Is the problem `simplifyICmpWithMinMax`? Does it call `simplifyICmpWithConstant`, and is the `UseInstrInfo` check there?

Also, could you kindly add tests for exhaustive signed-unsiged-samesign combinations?

https://github.com/llvm/llvm-project/pull/127007