Usually the identity hashcode is implemented by returning if present and
otherwise generating a random number, setting the hash code and
returning it.
This works fine in single-mutator environments, though when multiple
mutators might race to install identity hash codes we should ensure only
one of them wins and all others will obtain whatever hash code has been
set by the winner.
This will matter once we start sharing more objects across isolates.
Issue https://github.com/dart-lang/sdk/issues/36097
TEST=vm/cc/AsmIntrinsifier_SetHashIfNotSetYet
Change-Id: Ie760ca9658e6ec0640255361544d6822b07574e2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/201827
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Martin Kustermann
2505b6c64e