RFR: 8281429: PhiNode::Value() is too conservative for tripcount of CountedLoop [v2]

[Roland Westrelin]

> The type for the iv phi of a counted loop is computed from the types
> of the phi on loop entry and the type of the limit from the exit
> test. Because the exit test is applied to the iv after increment, the
> type of the iv phi is at least one less than the limit (for a positive
> stride, one more for a negative stride).
> 
> Also, for a stride whose absolute value is not 1 and constant init and
> limit values, it's possible to compute accurately the iv phi type.
> 
> This change caused a few failures and I had to make a few adjustments
> to loop opts code as well.

Roland Westrelin has updated the pull request incrementally with four additional commits since the last revision:

 - Update src/hotspot/share/opto/cfgnode.cpp
   
   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
 - Update src/hotspot/share/opto/cfgnode.cpp
   
   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
 - Update src/hotspot/share/opto/loopnode.cpp
   
   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
 - Update src/hotspot/share/opto/loopnode.cpp
   
   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7823/files
  - new: https://git.openjdk.java.net/jdk/pull/7823/files/a8722dba..1532675c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7823&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7823&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7823.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7823/head:pull/7823

PR: https://git.openjdk.java.net/jdk/pull/7823