[llvm] [SelectionDAG] Unify ISD::LOAD handling in ComputeNumSignBits. NFC (PR #175060)

[Craig Topper via llvm-commits]

topperc wrote:

> > why anyone would call ComputeNumSignBits on a pointer.
> 
> Because your addressing modes are broken and you need to figure out if you can use them

I checked and the liveout/livein code that inserts AssertZExtAssertSExt does call it on pointers because it doesn't know any better.

https://github.com/llvm/llvm-project/pull/175060