fixes https://github.com/llvm/llvm-project/issues/177838
- Replaced assert(TargetTypeSize == SourceTypeSize) with a conditional:
when sizes differ, compute a BitcastType with the target's element type
but sized to match the source's total bitwidth
- Instead of unconditionally returning after bitcast, only return early
if BitcastType == TargetType (same-size case), otherwise fall through to
the shuffle logic
- Updated the final assert to use AssignValue->getType() since that may
now be the intermediate type rather than SourceType
5496267025