RFR: 8253524: C2: Refactor code that clones predicates during loop unswitching [v2]

[Roland Westrelin]

> During unswitching, PhaseIdealLoop::create_slow_version_of_loop()
> calls PhaseIdealLoop::clone_predicates_to_unswitched_loop() twice, one
> for each loops, to clone some predicates above each loop. That code is
> fragile as it (implicitly) requires the fast loop to be processed
> first. I propose calling
> PhaseIdealLoop::clone_predicates_to_unswitched_loop() a single time
> and have it handle both loops in a single pass.

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

  code style

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/317/files
  - new: https://git.openjdk.java.net/jdk/pull/317/files/2e26a7cb..5ab947eb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=317&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=317&range=00-01

  Stats: 6 lines in 2 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/317.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/317/head:pull/317

PR: https://git.openjdk.java.net/jdk/pull/317