[llvm] [DAGCombiner] `visitSIGN_EXTEND_INREG` - fold `(sext_inreg (freeze (extload x)))` -> `(freeze (sextload x))` (PR #226208)

[via llvm-commits]

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VachanVY wrote:

```
CombineTo(N, Frozen ? N0 : ExtLoad); // N0 here is freeze if `Frozen`
```

No, using existing `freeze` operation, but to use `assertsext` better to keep separate freeze? So not using `assertsext` was the reason for wrong asm `shrl`... fixed

https://github.com/llvm/llvm-project/pull/226208