[llvm] Fix for logic in combineExtract() (PR #108208)

[Ulrich Weigand via llvm-commits]

uweigand wrote:

I still don't think we need a check for the BITCAST case; it shouldn't matter what the resulting type is.  The important thing is that
- wherever the type of `Op` is actually *used*, it is verified to be a byte type (this is already done); and
- the desired output type `VecVT` (including the `Index` which is based on `VecVT`) is a byte type - *this* is where we have a problem as it is only validated by one caller but not the other

In your test case, the cause of the crash is that `Index` (which comes from the caller) is based on a i1 vector type in `VecVT` - this is the actual bug.  Once we fix the caller, that problem should be resolved.


https://github.com/llvm/llvm-project/pull/108208