RFR: 8278296: Generalize long range check transformation

[Roland Westrelin]

8259609 (C2: optimize long range checks in long counted loops) only
covered the case of a counted loop with a positive stride and a range
check with a positive scale. This change generalizes the long range
check transformation to all 4 combinations of stride and scale signs.

The stride > 0, scale > 0 case (covered 8259609) was tweaked so it now
uses Qmax computed as the inclusive limit of j*K+Q. That helps in
generalizing the formulas to other cases.

The addition of PhaseIdealLoop::is_scaled_iv_plus_extra_offset() was
required for the case of negative scale in an int loop. The range
check then has the shape:

(CmpUL (AddL (ConvI2L (SubI ConI (LshiftI (Phi

with ConI, the zero constant.

This change also addresses this comment from John:

https://github.com/openjdk/jdk/pull/6576#discussion_r765343664

as part of 8276116 (C2: optimize long range checks in int counted loops)

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

Commit messages:
 - whitespaces
 - test & fix

Changes: https://git.openjdk.java.net/jdk/pull/6989/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6989&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278296
  Stats: 516 lines in 5 files changed: 380 ins; 76 del; 60 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6989.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6989/head:pull/6989

PR: https://git.openjdk.java.net/jdk/pull/6989