RFR: 8259609: C2: optimize long range checks in long counted loops

[Roland Westrelin]

JDK-8255150 makes it possible for java code to explicitly perform a
range check on long values. JDK-8223051 provides a transformation of
long counted loops into loop nests with an inner int counted
loop. With this change I propose transforming long range checks that
operate on the iv of a long counted loop into range checks that
operate on the iv of the int inner loop once it has been
created. Existing range check eliminations can then kick in.

Transformation of range checks is piggy backed on the loop nest
creation for 2 reasons:

- pattern matching range checks is easier right before the loop nest
  is created

- the number of iterations of the inner loop is adjusted so scale *
  inner_iv doesn't overflow

C2 has logic to delay some split if transformations so they don't
break the scale * iv + offset pattern. I reused that logic for long
range checks and had to relax what's considered a range check because
initially a range check from Object.checkIndex() may include a test
for range > 0 that needs a round of loop opts to be hoisted. I realize
there's some code duplication but I didn't see a way to share logic
between IdealLoopTree::may_have_range_check()
IdealLoopTree::policy_range_check() that would feel right.

I realize the comment in PhaseIdealLoop::transform_long_range_checks()
is scary. FWIW, it's not as complicated as it looks. I found drawing
the range covered by the entire long loop and the range covered by the
inner loop help see how range checks can be transformed. Then the
comment helps make sure all cases are covered and verify the generated
code actually covers all of them.

One issue is overflow. I think the fact that inner_iv * scale doesn't
overflow helps simplify thing. One possible overflow is that of scale
* upper + offset which is handled by forcing all range checks in that
case to deoptimize. I don't think other case of overflow needs special
handling.

This was tested with a Memory Segment micro benchmark (and patched
Memory Segment support to take advantage of the new checkIndex
intrinsic, both provided by Maurizio). Range checks in the micro
benchmark are properly optimized (and performance increases
significantly).

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Commit messages:
 - whitespaces
 - build fix + test cleanup
 - range checks

Changes: https://git.openjdk.java.net/jdk/pull/2045/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2045&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259609
  Stats: 770 lines in 10 files changed: 647 ins; 54 del; 69 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2045.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2045/head:pull/2045

PR: https://git.openjdk.java.net/jdk/pull/2045