[lworld] RFR: 8251398: [lworld] TestCallingConvention::test36 spuriously fails due to incorrect field value

[Tobias Hartmann]

In addition to integer registers, we also need to save vector registers used for floating point arguments before
calling into the runtime in the GC barrier slowpaths.

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Commit messages:
 - 8251398: [lworld] TestCallingConvention::test36 spuriously fails due to incorrect field value

Changes: https://git.openjdk.java.net/valhalla/pull/143/files
 Webrev: https://webrevs.openjdk.java.net/valhalla/143/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251398
  Stats: 44 lines in 1 file changed: 40 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/143.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/143/head:pull/143

PR: https://git.openjdk.java.net/valhalla/pull/143