[jdk18] RFR: 8278790: Inner loop of long loop nest runs for too few iterations

[Roland Westrelin]

Given a counted loop that iterates in [A, Z), when long range checks
are transformed into int range checks, a loop nest is created and
the inner loop iterates in [0, Z2).

The limits of the inner loop are adjusted to guarantee no overflow for
the range of values of the inner loop. That is for a range check:

i * scale + offset <u length

1) the bounds of the inner loop are adjusted to roughly [0,
max_jint/scale).

Also, we don't want to loose what we know about the bounds of the loop
being transformed.

2) So the bound of the inner loop are also adjusted to [0, min(Z2, Z - A))

The bug here is that 2) is performed before 1). This was spotted with
a micro benchmarks where the initial loop had only ~2000
iterations. The transformed loop is expected to run for the same 2000
iterations but instead ran for 2000/scale iterations.

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

Commit messages:
 - fix
 - alloc array fix

Changes: https://git.openjdk.java.net/jdk18/pull/35/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=35&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278790
  Stats: 209 lines in 10 files changed: 130 ins; 57 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/35.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/35/head:pull/35

PR: https://git.openjdk.java.net/jdk18/pull/35