RFR(L) [8u-backport] 8027754: Enable loop optimizations for loops with MathExact inside

[Rickard Bäckman]

Hi,

can I have this backport reviewed? Patches applies cleanly to 8u-dev.
Original commits to jdk9 done on 25th of Feb so the changes had some
time to bake.

Webrev: http://cr.openjdk.java.net/~rbackman/8027754.4/
Changeset: http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/cd5d10655495
Bug: https://bugs.openjdk.java.net/browse/JDK-8027754

Thanks
/R