[llvm] [CodeGen] Fix PreISelLowering not reporting changes (PR #102184)

[Roger Ferrer Ibáñez via llvm-commits]

rofirrim wrote:

Thanks @aengelke 

I'll take a look at `CachingVPExpander::expandVectorPredication` and see whether we can make it more reasonable so we don't assume we're changing things when the intrinsic is fully legal.

Currently it reads 

```cpp
// Return true if and only if the intrinsic was actually removed.
```

but I'm not sure why it should be like that. Maybe @simoll can shed some light here.

https://github.com/llvm/llvm-project/pull/102184