RFR: 8283187: C2: loop candidate for superword not always unrolled fully if superword fails [v4]

[Roland Westrelin]

> IdealLoopTree::policy_unroll_slp_analysis() restricts unrolling of
> loops that are found to be candidate for superword but if superword
> then fails, unrolling doesn't always resume. SuperWord::output() has
> logic for that in one of the failure paths but some other paths are
> not covered (for instance in the case of the test case). I propose
> that superword explictly returns whether it succeeded or not and that
> in case of failure, for a main loop, unrolling be attempted again.

Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:

  test fix on x86

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7822/files
  - new: https://git.openjdk.java.net/jdk/pull/7822/files/8ae4fa52..757f0310

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7822&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7822&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7822.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7822/head:pull/7822

PR: https://git.openjdk.java.net/jdk/pull/7822