[13] RFR (S): 8218874: C2: Unsafe to access PhaseIdealLoop outside of constructors

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8218874/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8218874

It's unsafe to access PhaseIdealLoop outside of its constructors: its 
internal data structures may be corrupted because 
PhaseIdealLoop::build_and_optimize() allocates some of them under local 
ResourceMark.

Proposed fix is:
   * use caller scope for memory allocation (as other Phases do);
   * to simplify PhaseIdealLoop usage, introduce static method 
optimize() and allocate PhaseIdealLoop there prepended by ResourceMark;

Testing: hs-precheckin-comp, tier1-5

Best regards,
Vladimir Ivanov