RFR: 8278784: C2: Refactor PhaseIdealLoop::remix_address_expressions() so it operates on longs

[Roland Westrelin]

The logic in PhaseIdealLoop::remix_address_expressions() that's
specific to int nodes apply equally to long nodes. This change
refactors that code so it applies to both integer types. This improves
performance on some of panama's micro-benchmarks.

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Commit messages:
 - test
 - remix address

Changes: https://git.openjdk.java.net/jdk/pull/6892/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6892&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278784
  Stats: 264 lines in 5 files changed: 178 ins; 34 del; 52 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6892.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6892/head:pull/6892

PR: https://git.openjdk.java.net/jdk/pull/6892