[llvm] [DAG] getNode - fold (sext (trunc x)) -> x iff the upper bits are already signbits (PR #151945)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Isn't this already done as a combine? Why does getNode need to do it? 

https://github.com/llvm/llvm-project/pull/151945