RFR: 8281322: irTests/TestLongRangeChecks.java fails with strip mining off

[Roland Westrelin]

Some of the long range check transformations take advantage of the
safepoint captured by loop strip mining to extract jvm state (in order
to add back empty predicates to the inner loop of a loop nest). As a
consequence, irTests/TestLongRangeChecks.java fails with strip mining
off and users might experience performance anomalies where changing
GCs affect purely computational code.

The strip mined loop nest creation is a 2 step process:

1- when a CountedLoop is created, an OuterStripMinedLoop is also added
  but it's not fully constructed

2- at macro expansion time, the OuterStripMinedLoop is turned into an
  actual loop by adding Phis and a proper exit condition

I propose always doing 1- whether loop strip mining is enabled or
not. This causes the safepoint to always be captured. Loop strip ming
is not expected to get in the way of loop transformations so this
change in itself should be performance neutral. Then at 2-, if loop
strip mining is not enabled, the OuterStripMinedLoop can be removed
and the safepoint moved back into the loop in case
LoopStripMiningIter=1 or simply removed too.

-------------

Commit messages:
 - test bug/summary
 - fix & test

Changes: https://git.openjdk.java.net/jdk/pull/7364/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7364&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281322
  Stats: 108 lines in 5 files changed: 99 ins; 5 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7364.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7364/head:pull/7364

PR: https://git.openjdk.java.net/jdk/pull/7364