[lworld] RFR: 8264414: [lworld] [AArch64] TestBufferTearing.java fails with C1

[Nick Gasson]

We see failures like this on AArch64 when MyValue.incrementAndCheck() is
compiled with C1:

  java.lang.RuntimeException: Inconsistent field values: expected 0 to equal 675128
        at jdk.test.lib.Asserts.fail(Asserts.java:594)
        at jdk.test.lib.Asserts.assertEquals(Asserts.java:205)
        at jdk.test.lib.Asserts.assertEQ(Asserts.java:178)
        at compiler.valhalla.inlinetypes.MyValue.incrementAndCheck(TestBufferTearing.java:81)
        at compiler.valhalla.inlinetypes.TestBufferTearing$Runner.run(TestBufferTearing.java:124)

The barrier that is usually inserted on return from a method that wrote
final fields should be sufficient to prevent another thread seeing the
zero-initialised intermediate state.  However this barrier isn't
inserted at the moment because method()->is_object_constructor() is
false for primitive class constructors.

C2 has a similar guard around the memory barrier in Parse::do_exits().
I'm not sure if that needs amending as well but I've not seen any
failures due to it.

-------------

Commit messages:
 - 8264414: [lworld] [AArch64] TestBufferTearing.java fails with C1

Changes: https://git.openjdk.java.net/valhalla/pull/376/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=376&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264414
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/376.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/376/head:pull/376

PR: https://git.openjdk.java.net/valhalla/pull/376