[InstCombine] add bitcast+extelt helper function; NFC

We can handle patterns where the elements have different 
sizes, so refactoring ahead of trying to add another blob
within these clauses.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342918 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed