code review for loop splitting code

[Berg, Michael C]

This modification splits simple loops into pre/main/post loops with main loop entry tests which use array length to compare with the maximal trip value to prevent iterations which require bounds checks from being executed in the main loop.  Some merge work will be done to bring in the enterprise version of range check elimination.  Both phases will be posed in mid tier.  This work stages the introduction and implementation loop unrolling, which will also occur on simple loops which do not have range checks.  Data flow/state relationships are managed in this code to maintain values defined in the pre/main/post loops.




The code is available as:



https://github.com/graalvm/graal-core/pull/264



For review.



Regards,

Michael