After reducing a miscompiled program down to the functions which are being

After reducing a miscompiled program down to the functions which are being
miscompiled, try to use the loop extractor to reduce the program down to a
loop nest that is being miscompiled.  In practice, the loop extractor appears
to have too many bugs for this to be useful, but hopefully they will be fixed
soon...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12398 91177308-0d34-0410-b5e6-96231b3b80d8