RFR(S): 8223140: Clean-up in 'ok_to_convert()'.

[Patric Hedlin]

Dear all,

I would like to ask for help to review the following change/update:

Issue:  https://bugs.openjdk.java.net/browse/JDK-8223140
Webrev: http://cr.openjdk.java.net/~phedlin/tr8223140/

8223140: Clean-up in 'ok_to_convert()'

     Simplify logic in 'ok_to_convert()'.
     Rename 'is_loop_iv()' to 'is_cloop_ind_var()'.
     Adding precond/postcond macros.


Testing: Part of 8216137 (hs-tier1..4, hs-precheckin-comp, Kitchensink24h)


Best regards,
Patric