RFR: addressing review comments

[Vicente Romero]

Fixing a compiler crash plus other review comments from Maurizio

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Commit messages:
 - addressing review comments

Changes: https://git.openjdk.java.net/valhalla/pull/663/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=663&range=00
  Stats: 95 lines in 2 files changed: 87 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/663.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/663/head:pull/663

PR: https://git.openjdk.java.net/valhalla/pull/663