[llvm] [DAGCombiner] Teach `reduceLoadWidth` to look past `ISD:FREEZE` (PR #189317)

[Henry Jiang via llvm-commits]

mustartt wrote:

> > @david-arm @RKSimon I'm wondering what's the exact semantics of `ISD::FREEZE`. In the IR, this transformation does not seem valid
> 
> It should be identical to the IR freeze

If its identical to the IR freeze, then `zext(freeze(load)) -> freeze(zextload)` in https://github.com/llvm/llvm-project/pull/175022 also invalid per the semantics of freeze. But since we are in the machine land, this is accepted? That's what I'm trying to answer.


https://github.com/llvm/llvm-project/pull/189317