No correctness fixes here, just minor qoi fixes:

* Don't insert a branch to the switch instruction after the call, just
  make it a single block.
* Insert the new alloca instructions in the entry block of the original
  function instead of having them execute dynamically
* Don't make the default edge of the switch instruction go back to the switch.
  The loop extractor shouldn't create new loops!
* Give meaningful names to the alloca slots and the reload instructions
* Some minor code simplifications

llvm-svn: 12402