[lworld] RFR: 8277570: [lworld] Pre-allocated instance should be created during class initialization

[Frederic Parain]

Please review those changes moving the creation of the pre-allocated default instance from the loading phase to the class initialization phase. The changes also include fixes in C1 to ensure the class is initialized before optimizing empty classes.

Thank you,

Fred

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Commit messages:
 - Move pre-allocation of default instance to initialization

Changes: https://git.openjdk.java.net/valhalla/pull/585/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=585&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277570
  Stats: 35 lines in 4 files changed: 24 ins; 8 del; 3 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/585.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/585/head:pull/585

PR: https://git.openjdk.java.net/valhalla/pull/585