RFR: 8281429: PhiNode::Value() is too conservative for tripcount of CountedLoop [v8]

[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 with a new target base due to a merge or a rebase. The pull request now contains 23 commits:

 - whitespaces
 - more review
 - Merge branch 'master' into JDK-8281429
 - review
 - undo unneeded change
 - Merge branch 'master' into JDK-8281429
 - redo change removed by error
 - review
 - Merge branch 'master' into JDK-8281429
 - undo
 - ... and 13 more: https://git.openjdk.java.net/jdk/compare/29c2e54c...6d145597

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Changes: https://git.openjdk.java.net/jdk/pull/7823/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7823&range=07
  Stats: 404 lines in 7 files changed: 385 ins; 1 del; 18 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